:::It remains to be seen whether or not string theory is a useful model of reality capable of offering testable predictions. In this context, showing that string theory is capable of making new verifiable predictions is basically the same as showing that strings "really exist". [[User:Dragons flight|Dragons flight]] ([[User talk:Dragons flight|talk]]) 16:28, 20 January 2011 (UTC)
:::It remains to be seen whether or not string theory is a useful model of reality capable of offering testable predictions. In this context, showing that string theory is capable of making new verifiable predictions is basically the same as showing that strings "really exist". [[User:Dragons flight|Dragons flight]] ([[User talk:Dragons flight|talk]]) 16:28, 20 January 2011 (UTC)
::::That's kinda the point; though it would be better to say that "really exist" misses the boat in that it implies only a single "right" answer; after all if strings really exist, than other models which do not contain strings, really don't exist. Having a paradigm that searches for the One Right Answer completely misses the point of science. Lets go back to the light example. Does light really and truly exist as a particle or does it really and truly exist as a wave? If you commit yourself to that mindset, you are left with three very unsatisfying results:
::::*Light is only one or only the other (observationally inconsistent; light clearly behaves like a particle in some situations, and like a wave in others)
::::*Light is both at the same time (logically inconsistent; a little ball and a mode of movement don't occupy the same class of nouns even. It's akin to claiming that something smells like the color red. It has a poetic appeal, but it doesn't make any logical sense)
::::*Light switches between the two modes, depending on the type of observation (seems better at first, but it begs the question about what light is doing when it isn't being watched.)
::::People have grappled with this concept for a very long time, the only satisfying result comes when you come to realize that there is a difference between reality and perception, and most importantly '''reality is not observable at all''' at the most fundemental level. All you can say is that your mind ''perceives'' an object or phenomena to be real, but you have no way to confirm that. Look at your keyboard. How can you confirm your keyboard exists, '''as an entity seperate from your internal, mind-created construct of what it is'''. At some point, you need to accept that as true. But that's still an unproven (and unprovable) proposition. When we deal with scientific concepts which are only observable in the second or third order, where we are further removed from the observable properties of it, these sort of problems become manifest in the situation. Back to light, rather than trying to decide what light "really" looks like, and "really is", change your paradigm to just accept that light is what it is, and is fundementally unconcievable apart from the models we make to describe it. Accept that, while light exists and is consistent, our models being by definition imperfect representations, can never fully capture what it means to be light, and let yourself be OK with that. Understand that the two competing and mutually exclusive models of light work in their own domains, are uncontradicted by other models, and so are as close to "real" as we can get, insofar as anything is "real". On that level, string theory may be "real", but also be willing to accept other, competing, and apparently mutually exclusive models as equally "real" insofar as they contradict neither logic nor observations. --[[User:Jayron32|<font style="color:#000099">Jayron</font>]]'''''[[User talk:Jayron32|<font style="color:#009900">32</font>]]''''' 16:48, 20 January 2011 (UTC)
Revision as of 16:48, 20 January 2011
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Not yet, I want more data about specific planets.--125.214.246.65 (talk) 07:17, 15 January 2011 (UTC)[reply]
Well, the individual articles for the planets contain information on their composition. Dismas|(talk) 07:40, 15 January 2011 (UTC)[reply]
Be careful with the data! Except earth all other planets are estimates. Deep drilling and seismic experiments are necessary to improve the estimates, but the deepest hole ever made on an other planet is 30cm deep and only the moon received seismometers. The spectroscopy of the surface gives only limited informations on the interior of differentiated body. --Stone (talk) 08:58, 15 January 2011 (UTC)[reply]
But some components shown in these articles were compounds, not elements.--125.214.246.65 (talk) 14:19, 15 January 2011 (UTC)[reply]
Compounds are combinations of elements. At least in some cases, the evidence cannot even distinguish a pure element from a compound containing it (if the test is for properties of the element/nucleus/atom rather than the overall form of it). And in other cases, the atoms aren't even in a stable elemental form (plasmas and such) even if they are conceptually the pure element (rather than a compound). DMacks (talk) 18:04, 15 January 2011 (UTC)[reply]
Can sulfuric acid be made anhydrous with the use of anhydrous copper(II) sulfate as a dessicator? --Plasmic Physics (talk) 09:03, 15 January 2011 (UTC)[reply]
I have not directly searched for detailed information on the question, but as far as I can remember, anhydrous copper(II) sulfate is not commonly used as a desiccant and probably not a so powerful desiccant. Where do you intend to add the dessicant ? Directly in the bottle of the H2SO4 to "dry" or spread in a cup installed in a close dessicator beside another open recipient containing H2SO4 ? I do not advise to directly add the anhydrous copper sulfate, nor any other desiccant, into the sulfuric acid. It will likely partly dissolve into the sulfuric acid and contaminate it. What is the aim pursued in doing so? When asking a question to a chemist, it is always good to inform him about the pursued objective to receive a well founded advice and not only a technical and perhaps inadequate answer.
Safety: remember, concentrated H2SO4 and oleum are also strong oxidizers and can violently react with many chemicals. I remember to have transformed cellulose kleenex in black carbonchar when trying to clean spills of concentrated sulfuric acid on the bench in the lab. Regards, Shinkolobwe (talk) 17:06, 15 January 2011 (UTC)[reply]
Look also at oleum production and at sulfur trioxide or disulfuric acid. Oleum was also historically produced from the distillation of iron sulfate. Similarly, it could perhaps be concentrated by distillation over a powerful desiccant such as anhydrous magnesium sulfate. Magnesium strongly retains 6 water molecules in its hydration crown. Shinkolobwe (talk) 17:40, 15 January 2011 (UTC)[reply]
Copper sulfate is used as a dessicant in a few specific types of organic-chemistry reactions (acetal formation for example). I don't know a measure of its absolute strength, but in my experience it's harder to dry copper sulfate than it is to dry other inorganic solid desiccant (molecular sieves, silica, or indicator-doped drierite). Sulfuric acid is a much more common a very strong dehydrating agent and dessicant for all sorts of materials. DMacks (talk) 18:00, 15 January 2011 (UTC)[reply]
In my opnion, the harder it is to dry a desiccant, the more effective it is. I chose the desiccant to be a sulfate, to prevent reactions taking place with the sulfuric acid, excluding decomposition. I want to try adding sulfuric acid over anhydrous copper sulfate, followed by vacuum filtration through a teflon buchner funnel. The end goal is to produce an acid with sufficient concentration to react with KNO3 to produce nitric acid for distallation in a retort.
I know I can simply buy the concentrated acid, but this is part of my process, I do things the hard way. Some people collect stamps, I collect chemicals, solids only, but sometimes I need a little liquid to make a solid. I am not a novice, I have studied chemistry both formally and informally for many years now, only two years at university though.
I distilled nitric acid in this way before, but I used 4.6 M sulfuric acid instead. This gave a dissapoiting 5 mL of pure nitric acid. I know it was nitric, because I spilled a single drop on the hot plate and it instantly rusted it, underneath the paintwork, causing it to bubble. --Plasmic Physics (talk) 21:20, 15 January 2011 (UTC)[reply]
If you are equipped with a distillation apparatus, why not to simply remove the water from the mid-concentrated sulfuric acid by distillation ? To remove water with a solid desiccant would require a large molar ratio desiccant/sulfuric acid and is not an effective technique. The vacuum pump will also require a protection trap to avoid to inadvertently aspire sulfuric acid or an aerosol into the costly pumping mechanism. Better also not to use a water trump directly connected to the buchner vessel to avoid a possible and hazardous backlash of water from the trump into the concentrated sulfuric acid. Take care. Just by curiosity: To what synthesis has to serve the nitric acid you need to produce ? Shinkolobwe (talk) 22:17, 15 January 2011 (UTC)[reply]
I tried distilling the sulfuric acid before, but the process gives off too much corrosive vapour. Is there a different way then, that excludes boiling off the water? I intend to produce bismuth nitrate, neodymium nitrate, and lanthanum nitrate. --Plasmic Physics (talk) 03:07, 16 January 2011 (UTC)[reply]
I'd really discourage anyone from the experiments I can imagine after reading this discussion. Because the actual question–seems to me–is how to achieve the goal without proper laboratory equipment and technique. Anyways, feasible methods for making a concentrated sulfuric acid out of dilute sulfuric acid are: 1) distilling water off, 2) adding SO3 or oleum. Dessicants are used for removing of traces of water from the medium they're not migrating into. If the initial sulfuric acid in question is dilute, then by pure logic it isn't impossible to obtain a concentrated copper sulfate solution in relatively more concentrated sulfuric acid. But it would take unreasonable amounts of copper sulfate and the result will definitely not be anhydrous. On the other hand, it doesn't take 100% H2SO4 to displace nitrates in the desired fashion. Dynamic equilibrium will produce more of HNO3 being steadily removed by distillation in the retort. Legate of Skai (talk) 14:20, 17 January 2011 (UTC)[reply]
The problem with copper sulfate (or sulfates in general) is the basicity of the SO42- ion. With H2SO4 being a strong acid, it's very likely that the H2SO4 will simply protonate the SO42- ion to form 2 HSO4- ions (hydrogen sulfate), so basically you will kind of neutralize your sulfuric acid instead of concentrating it (for the same reason you can't use NaOH/CaO to dry H2SO4 even though those are also quite hygroscopic. You'll get a nice explosion though with sulfuric acid splattering around). The only possibility of drying it chemically which comes to my mind would be using an acidic drying agent such as phosphorous pentoxide, but I have no idea how to seperate it from the acid afterwards. This leaves the addition of SO3 but this is 1) difficult to produce and 2) difficult to handle. Setting up a contact process at home just to get some better yield of conc. HNO3 is slightly overkilling it IMO.--178.26.171.11 (talk) 19:47, 19 January 2011 (UTC)[reply]
OK, anhydrous is ideal, but not required.
Legate of Skai: What if the same amount of copper sulfate is reused? Add anhydrous copper sulfate to the sulfuric acid untill the hydrated copper sulfate precipitates. Filter out and dry the ppt so that it may be reused. Repeat untill maximum concentration is reached.
178.26.171.11: I don't understand how copper sulfate would neutralise sulfuric acid. Even though I have a chemical vendor at my disposal, it is key that I source my reagents myself; phosphorus pentoxide is even harder to obtain than quality sulfuric acid.
What about cold distillation? Cool the acid solution untill a crust of ice forms, then remove this. Even though the crust contains a fraction of the sulfuric acid, the concentration is different compared to the solution. Repeating this process should gradually change the acid solution concentration. --Plasmic Physics (talk) 09:26, 20 January 2011 (UTC)[reply]
It works like that: H2SO4 (sulfuric acid) can give away 2 protons. The first stage, where sulfuric acid gives off one proton, yields the HSO4- (hydrogen sulfate or bisulfate) ion (here with water as the base):
The pKa of that reaction is very low (-3), making H2SO4 a strong acid. In the second step, another proton can be removed from the remaining hydrogen sulfate ion:
Chemical equilibrium on the right at normal pH, rather on the left at low pH
Here, the pKa is 1.9, therefore HSO4- is of medium to high acidity, making the sulfate (SO42-) ion a weak to medium corresponding base. And if a molecule of sulfuric acid and a sulfate ion meet, following neutralization (or acid-base) reaction will happen:
Chemical equilibrium on the far right
Therefore, if you add copper sulfate to concentrated sulfuric acid, you'll get a solution of copper hydrogen sulfate in sulfuric acid, not quite what you want.
The freezing method will not work too well because the sulfuric acid doesn't have much of a tendency to separate from water (very endothermic) so you probably won't get much of a concentration change between liquid and solid phase and your yield will quickly go towards zero if you have to repeat the process multiple times for just a small bit of separation. This is all assuming you want to get close to 100% sulfuric acid.
But if you just want to concentrate sulfuric acid to let's say 90% (should be enough for your purpose of getting HNO3), simply heat it and evaporate away the water just until SO3 fumes start to form (around 300°C). Needless to say that this is quite dangerous because 1) oven-hot H2SO4 might splatter around because with rising concentration, viscosity will also rise and change the boiling behaviour and 2) SO3 fumes are extremely corrosive and toxic, but I just AGF right now and believe that you know what you're doing.
The acid obtained that way should be able to let you distill HNO3 out of your nitrate salt/sulfuric acid mixture. Just make sure your nitrate salt is dry and doesn't contain crystallization water which besides lowering the yield could also violently react with the sulfuric acid on mixing. KNO3 is probably the best choice, NaNO3 is rather hygroscopic and should be freshly dried (by heating to ~200°C) before usage.
Another more "elegant" method would be using barium nitrate and a slight excess of the dilute(!) sulfuric acid which you already have. This will form unsoluble barium sulfate and you can simply filter (a glass wool funnel + vacuum pump would be the best choice) and then distill the nitric acid. 178.26.171.11 (talk) 18:19, 20 January 2011 (UTC)[reply]
Thank you, that brings me to my next problem: When I reacted the mixture of sulfuric acid and potassium nitrate, it produced a solid cake of potassium bisulfate which was very hard to remove by mechanical means. Is there a chemical that should break it up, like sodium hexametaphosphate? --Plasmic Physics (talk) 04:52, 21 January 2011 (UTC)[reply]
Oh, sorry for the late reply but I couldn't find the discussion easily any more after it was archived. But to answer your question: what about H2O? According to our article, the solubility is very high. BTW, after dissolving the bisulfate you can recycle it by re-evaporating the water and heat the bisulfate to very high temperatures to make it decay into potassium disulfate + water first and on further heating to potassium sulfate and sulfur trioxide with which you could concentrate your sulfuric acid. 178.26.171.11 (talk) 00:55, 25 January 2011 (UTC)[reply]
I tried to disolve it in water, but there was no change in volume of ppt. The cake consisted of micro crystals which, precipitated during distillation. I don't think that I would have enogh potassium bisulfate to recycle into acid.
Is it expected for and acid resistant, round bottom flask to be attacked during this type of reaction? My initial setup included a round bottom flask and a graham condenser, now a retort. After the first use according to this experiment, the flask was observed to have lost 2 mm of its thickness near the bottom. This neww weakness, caused the flask to break when an attempt was made to mechanically destroy the cake. --Plasmic Physics (talk) 06:17, 25 January 2011 (UTC)[reply]
Hmm, that seems strange to me... because actually the bisulfate should readily and exothermically dissolve in water, even more so if the crystals are small (higher overall surface area which leads to higher reaction speed). Was the potassium nitrate maybe contamined with other cations, such as calcium or barium? To test it simply dissolve a small amount of the salt in water and add a drop of sulfuric acid - if the KNO3 was "clean" (i.e. free of heavy earth alkaline metals, lead or any other cations that form insoluble sulfate salts) then there should be no ppt.
Furthermore the glass shouldn't have been attacked by sulfuric or nitric acid, you can even store very strong and oxidizing acids such as aqua regia or perchloric acid in glassware. (Strong bases, on the other hand, do attack glass, especially at elevated temperatures) Out of my head the only acid that attacks glass is HF but I don't think that your nitrate was contamined with fluoride (that stuff, especially in its protonated form HF, is highly toxic) so, assuming that you didn't heat the glass to extremely high temperatures (>800°C), I have no idea how this could've happened. So that leaves the question: Is your potassium nitrate pure? Where did you get it from? The only explanation I could think of is that you used toothpaste as a KNO3 source, this would explain both the unsoluble cake (calcium fluoride) and the etched glassware (hydrogen fluoride). 178.26.171.11 (talk) 22:58, 26 January 2011 (UTC)[reply]
Good theory, why didn't I think about it? I used fertilizer grade potassium nitrate, obtained from a hydroponics retailer. What's the chance of this type of potassium nitrate being contaminated with fluoride salts? Could it be purified using recrystalisation? --Plasmic Physics (talk) 04:13, 27 January 2011 (UTC)[reply]
OK, but somehow I doubt that any fertilizer bought in a developed country has fluorides in it because of their toxicity and you don't want them in your food later on. Unless your source is dubious of course. I'm not from the US so I don't know about "hydroponics". What does it say on the label, something like "100% potassium nitrate" or is it a mixture? At least here in Germany, you usually only get mixtures instead of pure nitrates, government paranoia might play a role... Did you try to dissolve some of the fertilizer in pure water, and did it work? 178.26.171.11 (talk) 18:00, 27 January 2011 (UTC)[reply]
It was obtained by the kilogram, from a bulk dispenser plainly labeled pottassium nitrate. Here in New Zealand, people aren't overly concerned with terrorism; I also managed to obtain ammonium nitrate from the same retailer. I have not tried dissolving it just yet, I'm away from my lab for the time being. --Plasmic Physics (talk) 21:17, 27 January 2011 (UTC)[reply]
slingshot effect & Manned Space Travel
How fast can a spacecraft travel using the slingshot effect ?
Because I would like to know if the slingshot effect be used for (a) manned space missions around the solar system and (b) to reach other systms ?Scotius (talk) 13:07, 15 January 2011 (UTC)[reply]
The slingshot effect is currently an essential part of any travel to the outer planets; see Interplanetary spaceflight#Economical travel techniques. The slingshot effect can change a spacecraft's velocity by up to twice the planet's orbital speed. The orbital speed of Mars, for example, is about 24 km/s. The main disadvantage of the slingshot effect is that there usually aren't planets in an appropriate position for getting to where you want to go.
My mom thinks it's bad to eat cold foods such as ice cream on an empty stomach or cold dishes that have not been reheated. I doubt that most people reheat their dishes to what is needed to kill pathogens. Imagine Reason (talk) 14:03, 15 January 2011 (UTC)[reply]
Not sure what your question is, but it is certainly true that cooked food should be thoroughly reheated before eating. Very cold food and drink is not good for your stomach, at least according to Chinese medicine, but this is the science desk (ducks)...--Shantavira|feed me 15:02, 15 January 2011 (UTC)[reply]
"certainly true that cooked food should be thoroughly reheated before eating". Not so certain, I think, as I sit here and type following the old habit from college days of eating cold pizza for breakfast. 75.41.110.200 (talk) 15:48, 15 January 2011 (UTC)[reply]
Reheating will only kill pathogens if you heat the food to somewhere near the boiling point and keep it there for 10 minutes. But that's only necessary if the food has been sitting around for long enough to develop significant levels of bacterial contamination. Looie496 (talk) 17:44, 15 January 2011 (UTC)[reply]
Very dubious, since many (most?) prepared foods that people enjoy cold are cooked at some point in their preparation. Even ice cream (traditionally prepared) is cooked before it's frozen. Would you suggest "thouroughly reheating" my cookies & cream? (Even those cookies were once cooked!) Staecker (talk) 21:21, 15 January 2011 (UTC)[reply]
I doubt that ice cream is still frozen when it reaches the stomach. And if it is, it certainly won't keep frozen for a long time. Quest09 (talk) 22:34, 15 January 2011 (UTC)[reply]
Please ask her as to whom she heard this from – (and report back here). It may be due to an old wives' tale based on and accurate observation but one which got cause and effect arse about face. Rather than me attempt to explain why, the article pagophagia will indicate why your doctor asks people she suspects of having iron deficiency anaemia how often they eat ice-cream/ eat ice cubes etc. An' remember: Mom may not always be right but she is never, ever wrong! --Aspro (talk) 22:53, 15 January 2011 (UTC)[reply]
The point is probably to prevent the cold food from lowering the core body temperature and not to kill any pathogens (why microwave your ice cream?). There could then be a correlation between body temperature and the immune system etc. but any such effect is likely to be slight. ~AH1(TCU) 02:23, 18 January 2011 (UTC)[reply]
If I recall correctly from my SafeServ training the requirement for reheating is 165* F internal temperature, a far cry from boiling, but still fairly hot. According to the US FDA that would kill most bacteria in seconds [[. There were also rules for holding at a temperature lower than that, around 140, for a longer period, if I recall but it's been long enough I've forgotten. Remember 40-140* F is the danger zone, food kept in that range at all (including while it cools)
Yes it's true that most foods served cold are cooked at some point, however it's key to note that a factory making food products or a good chef takes steps to limit potential bacteria growth. 40-140* F is the danger zone, the temperatures that allow for the best possible bacterial growth, and the longer food lingers there the greater the risk. Foods cooked then cooled are usually best stored in a manner that prevents bacteria from entering and cooled quickly as practical (using icewater baths around the bowl, for instance). Leftovers are best kept hot and then cooled quickly. Heating to 165*F (a far cry from boiling but pretty darn hot) should kill most bacteria instantly according to the FDA, so why take a chance, heat leftovers well and you'll be far better off for it, even if the risk is small, it's not absent altogether. 65.29.47.55 (talk) 03:09, 19 January 2011 (UTC)[reply]
Half-life
According to half-life, will a given substance eventually decay into nothing? I know the conservation of energy, it will be in the form of energy, but will the substance cease to exist at some point? I believe this is true according to the 2nd law of thermodynamics and heat death, but I just want to confirm it. Also does all matter have a half-life? ScienceApe (talk) 14:59, 15 January 2011 (UTC)[reply]
Half-life is usually referring to radioactive decay. If a radioactive nucleus decays, it will split into decay products - usually one or two smaller nuclei, plus a number of elementary particles and some energy in the form of photons. So it will not decay into "nothing". Stable nuclei do do not decay on normal time scales. In particular, it's an open question if H+ (the proton) decays at all. If it does, the ultimate end product is electromagnetic radiation. --Stephan Schulz (talk) 15:11, 15 January 2011 (UTC)[reply]
Yeah I know it doesn't decay into nothing, that's why I said it will be in the form of energy, but... If I were to use an example, you have a block of iron. Will the iron at some point cease to exist as iron? Will at some point, it will exist entirely as photons? ScienceApe (talk) 17:32, 15 January 2011 (UTC)[reply]
According to Proton#Stability, the decay product of a proton is still a particle not just radiation (see also Proton decay for discussion of theoretical possibilities, including that it might actually be stable). A sample of the element iron is not going to change into "not iron"--it is composed of several isotopes, of which ~94% of the material is indefinitely stable, the remaining ~6% is usually called "stable" too, but technically is an isotope that decays to chromium with a half-life of 3x1022 years. DMacks (talk) 17:43, 15 January 2011 (UTC)[reply]
Hmm, but the first possibility mentioned is that it decays into a neutral pion and a positron. The pion would most likely decay into two photons; the positron could meet up with an orphaned electron. So at a first glance it appears you could still wind up with just radiation. (Maybe the probability of positron/electron encounters goes down so fast, in the increasingly empty universe, that that reaction never goes to completion, not sure about that.) --Trovatore (talk) 21:19, 15 January 2011 (UTC)[reply]
So a chunk of iron floating in space will always exist? I thought according to heat death, all the matter in the universe will eventually decay into photons? ScienceApe (talk) 18:48, 15 January 2011 (UTC)[reply]
No. In the standard model, conservation laws such as that of the baryon number prevent ordinary matter from turning entirely into photons. There is nothing in the concept of heat death that requires everything to become photons -- it just says that the universe will end up with the highest possible entropy; states that are not possible to reach do not count even if they would have had even higher entropy. –Henning Makholm (talk) 21:10, 15 January 2011 (UTC)[reply]
I seem to recall that in an old revision of the heat death article it stated that only the "lowly photon" is what will remain of the universe or something like that. I guess it was wrong. ScienceApe (talk) 21:22, 15 January 2011 (UTC)[reply]
The hunk of iron is space may eventually fall into a star, or black hole, and suffer the consequences of that. The black hole could then give out Hawking radiation. An alternative is that the future von Neumann machines will find the iron and covert it to one more of itself. Graeme Bartlett (talk) 21:42, 15 January 2011 (UTC)[reply]
"Lowly photon" will happen only if protons do actually decay. But there is currently no evidence for that, only some theoretical ideas. Ariel. (talk) 00:08, 16 January 2011 (UTC)[reply]
So if proton decay is in fact true, then it's safe to say that everything eventually should evaporate into photons at some point? ScienceApe (talk) 05:33, 16 January 2011 (UTC)[reply]
No, neutrinos and electrons will stick around. Ariel. (talk) 18:44, 16 January 2011 (UTC)[reply]
Radioactive decay typically ends at the stable isotope, but proton decay is theorized to occur at 1033 years. ~AH1(TCU) 02:21, 18 January 2011 (UTC)[reply]
RADIAL TYRES
Why radial tyres are called so.. I know they are different from Bias tyres as radial tyres has steel wires and Bias tyres have nylone tyres . . but I don't understand what it has to do with the word "RADIAL". I also want to know what are radial tubes.. — Preceding unsigned comment added by Amit.meer (talk • contribs) 15:44, 15 January 2011 (UTC)[reply]
The choice of materials is a separate issue from the terms you are asking about. We have an article cleverly titled "radial tyre", which discusses the geometric construction difference between the bias and radial reinforcement types. I'm not sure what the specific term "radial tube" means. DMacks (talk) 17:31, 15 January 2011 (UTC)[reply]
(edit conflict) Radial tire explains that they are called radial because of the radial direction of a layer of cords for reinforcement. According to the article, radial tires have radial ply AND bias plies, while bias tires only have bias ply. Though radial tires usually incorporate steel reinforcement, the term seems to apply to radial ply nylon-reinforced tires as well. SemanticMantis (talk) 17:38, 15 January 2011 (UTC)[reply]
Momentum
Why is momentum abbreviated p? I realize that m is traditionally used for mass but some letters are used to abbreviate more than one thing, and why was p in particular chosen, rather than any other letter? Merci .24.92.70.160 (talk) 17:55, 15 January 2011 (UTC)[reply]
I think its pretty arbitrary, but as you note you COULDN'T use "m" for momentum, since "m" stands for mass and mass and momentum often appear in the same equations. If you find "m" being used for something else, it would be in some other system which did NOT use mass. There are other arbitrary letter associations as well, for example "q" for "heat energy" and "U" for "internal energy" and things like that. I assume that the people who chose them first usually try to pick a letter which makes sense (like "F" for force), but in places where there is likely to be conflict, they may just choose something completely random and unlikely to be confused with other symbols. --Jayron32 20:16, 15 January 2011 (UTC)[reply]
In some languages (such as German or Danish), momentum is called "Impuls". There's a p there right at the beginning of the stressed syllable. In pre-Newtonian mechanics and kinematics, the word of choice for the concept seems to have been "impetus". –Henning Makholm (talk) 21:21, 15 January 2011 (UTC)[reply]
Just an observation and speculation: Sommerfeld, in vol. 1 (Mechanics) of his lectures on theoretical physics, uses G in all the chapters on the Newtonian formulation of mechanics and only switches to p when he gets to the Lagrangian and Hamiltonian formulations. Is it possible, that p has been introduced because it makes a nice symmetrical pair with q? Similarly, G could have been used because it follows F, making a pretty formula. One would have to look through older books of mechanics to see what was actually used there. --Wrongfilter (talk) 11:55, 16 January 2011 (UTC)[reply]
Power to weight ratio
I'm a little unclear on this. Is having a high power to weight ratio good for heavy vehicles? Like if an engine has a low power to weight ratio it might be ok on a light vehicle, but it would be terrible on a heavy vehicle? ScienceApe (talk) 18:46, 15 January 2011 (UTC)[reply]
Define "good" and "terrible"? What parameter are you measuring? Fuel consumption? Acceleration? Towing/loading capability? Engine and drive-train wear and tear? A lower-power engine might use less fuel (depending on the gearing and how much you need to stomp on the accelerator pedal), and could put less strain on your drive-train simply by not being very powerful. On the other hand a more powerful might use more fuel to the advantage of loading capability and acceleration. Paradoxically a more powerful engine could reduce drive-train wear and even fuel consumption simply by having the luxury of longer gearing. But we need to knowwhat you're after to properly answer the question. Zunaid 19:25, 15 January 2011 (UTC)[reply]
Here's the article, of course: power-to-weight ratio. I'd draw your attention to "Different designs trade off power-to-weight ratio to increase comfort, cargo space, fuel economy, emissions control, energy security and endurance." Perhaps ignore the "energy security" part - I have no idea what that's trying to say - but "fuel economy" sounds particularly important.
Pointlessly heavy engine: bad.
Engine which is heavier to yield some benefit besides power: good.
Engine which, heavy or light, leaves the vehicle underpowered: bad.
On the whole I think the power-to-weight ratio of the engine matters less in heavy vehicles, like trucks, since they would be hauling a cargo anyway (perhaps a cargo of engines?) - it matters a lot if the vehicle is relying on lightness for performance, where the weight of the engine accounts for a large part of the total weight of the vehicle. 213.122.57.166 (talk) 19:40, 15 January 2011 (UTC)[reply]
I guess the problem is I don't really understand what the ratio means (I read the article but I don't understand it). So if a vehicle has a high power to weight ratio does that mean it has high acceleration? Does it have high velocity? If you have a car and a heavy truck that both use the same exact engine with the same power to weight ratio, what will the performance be like on the car and the heavy truck? ScienceApe (talk) 21:20, 15 January 2011 (UTC)[reply]
I think you might be confused by the fact that the term "power to weight ratio" is used both to describe engines and vehicles. When it is used in reference to an engine, it is a ratio of the engine weight to its power (Engine weight/Power). When it is used in reference to a vehicle it is a ratio of vehicle weight (including the engine) to power (Vehicle weight/Power). Engine power to weight is used to compare the power density of propulsion units and doesn't directly relate to a individual vehicle's performance. Vehicle power to weight is part of determines a vehicles acceleration. If you have a car and a heavy truck with identical (vehicle) power to weight ratios they will likely have similar performance (compare a 2000kg car with a 200 hp engine to a 4000kg truck with a 400 hp engine), but it wont be identical. Power to weight ratio is only a rough estimate of actual real world performance for a number of reasons. For one thing the "power" figure is the peak output of the engine, the output varies depending on the engines RPM (some engines produce a broad band of power over the RPM range some do not). Other factors effect acceleration and top speed, such as aerodynamics, rolling resistance and drive train efficiency. --Leivick (talk) 21:34, 15 January 2011 (UTC)[reply]
As another example:Back in the days when engines where expensive to replace, a diesel engine locomotive would have big heavy slow revving engines (say 500 hp) which would last tens of thousands of hours between major overhauls, whilst piston engined fighter aircraftwith high revving (say 500 hp) engines would be much lighter but need rebuilding after only about 500 hours. So the power to weight ratio was an rough and ready way to guess what the engine was best suited for -but not very scientific, as it was dependant on how well the engine was manufactured. For instance: during the second world war, the British government gave the USA all the Rolls Royce technology, because their engine had such superior power to weight ratios and durability. However, US did not machines the components to Imperial inches and that meant the parts were not interchangeable.--Aspro (talk) 23:21, 15 January 2011 (UTC)[reply]
I'm curious, Aspro. I know that there is a US survey inch, but I can't imagine manufacturers using this rare "inch", nor can I imagine Americans using metric units at that time. Were American machine tools just less accurate? Dbfirs 09:38, 16 January 2011 (UTC)[reply]
The inch the US was using during World War II was what we would now call the "survey inch" (100⁄3937 m), and it was different to to the Imperial inch in use in the UK (approx. 0.9143969⁄36 m). But the Imperial inch was not a stable length standard: it was getting shorter by about 1 ppm every 23 years. I don't know for sure, but I can imagine a problem if Rolls Royce were saying that components had such-and-such dimensions in inches, but were actually machined on tools that were calibrated in metric units (as the metric calibration was already known to be more stable). Physchim62(talk) 12:52, 16 January 2011 (UTC)[reply]
Ah, thanks. I hadn't realised that it was not until 1959 that "inch" meant the same on both sides of the pond. I wouldn't have thought that Rolls Royce would be metric at that time, but I can imagine that engineers adjusted measurements depending on the wear on particular machine tools. Dbfirs 15:46, 16 January 2011 (UTC)[reply]
Particle decay
When a particle decays into other particles, it's said that the new particles were created, and that the old particles are destroyed. What observable differences would there be if the original particle was composed of the particles it decayed into? 74.15.137.130 (talk) 19:20, 15 January 2011 (UTC)[reply]
It doesn't seem really enlightening to me, I'm afraid. A possible answer to the original question would be that if the muon was a composite of the electron, antineutrino and mu-neutrino that it decays into, then it sould be possible to understand the difference between the magnetic moment of a muon and an electron as an effect of rotational and/or vibrational effects within the composite muon. In particular, there would be a spin-orbit interaction between the electron's intrinsic spin and its movement within the muon, which would give rise to several different kinds of muons with slightly different masses (and probably other properties, such as decay rate). Such a difference ought to be observable but hasn't actually been observed. –Henning Makholm (talk) 22:04, 15 January 2011 (UTC)[reply]
Is that how they discovered that the proton wasn't fundamental? And is the total rest mass in a decay constant? 74.15.137.130 (talk) 22:11, 15 January 2011 (UTC)[reply]
No, that was discovered by deep inelastic scattering i.e. shoot small somethings at neutrons and see how they bounce. The total mass - not rest mass - is conserved. To answer your original question, there wouldn't be much difference. Particles are interchangeable and indistinguishable, so there is no difference between "destroy particle, and create a new one" and "keep the original particle". Ariel. (talk) 00:13, 16 January 2011 (UTC)[reply]
Many unstable particles can decay into more than one different possible combination of byproducts. Dauto (talk) 06:12, 16 January 2011 (UTC)[reply]
Melting and snowing?
It must be possible to do so at the same time. Cause it's doing it right now. How exactly is it possible?
Happens all the time. I don't see any reason why it couldn't be cooler higher up in the air and warmer on the ground. Clarityfiend (talk) 20:58, 15 January 2011 (UTC)[reply]
It is possible because it is colder up in the clouds where the snow crystallizes. Looie496 (talk) 21:04, 15 January 2011 (UTC)[reply]
(Edit conflicts) The ground in winter is typically a little warmer than the air above it - see Heat_pump#Ground_source_heat_pumps - and the air at the height at which the snow forms (possible several thousand feet up) is generally cooler than the air near the ground - see Troposphere#Temperature - so the snow has formed where it is below freezing and is dropping into an environment where it is a little above freezing. 87.81.230.195 (talk) 21:05, 15 January 2011 (UTC)[reply]
Are there sharks that live in The Black Sea or Crimean Sea?
This is a question ive tried searching for the answer to,with no definitive results. my email is <redacted>—Preceding unsigned comment added by 208.98.220.141 (talk) 22:14, 15 January 2011 (UTC)[reply]
Contact information removed, all responses to your question will be posted here. WikiDao☯ 23:43, 15 January 2011 (UTC)[reply]
A preserve where I love to hike is currently being devastated by sudden oak death. I don't want to spread the pathogen, Phytophthora ramorum, around to other places. I can wash my boots but I don't know whether that's enough. Does anyone have any information on what kills it? Something simple that won't hurt either me or my boots (much), maybe rubbing alcohol? --Trovatore (talk) 02:51, 16 January 2011 (UTC)[reply]
If you find out, the information would be a valuable addition to the article. Dismas|(talk) 05:51, 16 January 2011 (UTC)[reply]
This intrigued me, so I poked around a bit. There is some information on Late blight of potato, caused by a very similar fungus-like-thingy. As a preventative measure, it suggests any fungicide, of which an interesting option is ordinary milk (see the sources), as well as various natural oils. The other low-damage approach may be special-order UV light. Just don't tell any customs agents where you've been - does someone know what happens if you re-enter the country and say "yes" to having been on farms? SamuelRiv (talk) 07:26, 16 January 2011 (UTC)[reply]
I've been in that situation twice, having arrived in the U.S. after having hiked across farmland in Scotland and Peru. All that happens is the customs agent uses some kind of disinfectant on the bottoms of your hiking boots, and then gives your boots back to you. The disinfectant doesn't seem to have any adverse affect on the boots that I've noticed, and it doesn't delay the entry procedure by more than about a minute. There's no good reason to lie to the customs agent about having hiked across farmland, and you help avoid the possibility of spreading some pathogen to U.S. soil by telling the truth. Red Act (talk) 15:05, 16 January 2011 (UTC)[reply]
I had to disclose that I was on a farm and in contact with livestock when returning to the US after a trip to the Netherlands. They didn't seem to care, but they may have been distracted while asking if I had brought any "blown glass tobacco-smoking paraphernalia". Always tell the truth - it's not a hassle and lying to government officials gets you nowhere. Freedomlinux (talk) 08:40, 17 January 2011 (UTC)[reply]
Ooh, for soil molds: "The way to sterilize soil is to cook it. I have always been told 175 degrees F for 2 hours."[2] Can your boots withstand it? SamuelRiv (talk) 07:30, 16 January 2011 (UTC)[reply]
Brushing anything off clothing. Cleaning dirt off boots and any equipment and wiping over with ordinary dilute bleach. Flaming everything with napalm doesn't seem necessary. --Aspro (talk) 15:25, 16 January 2011 (UTC)[reply]
As Mass of Earth = Me = g r² / G. But Me varies when on-center distance between the two masses varies e.g moon on earth - is this right?
Question Two
Shouldn't the force that the object of mass m resists the accelaration due to gravity be = (Me)g1= weight of earth on the body of mass m, where g1= G (m) / r², accelaration due to gravity of a body of mass m OR accelaration of earth towards centre of a body of mass m. Where r is on-center distance between the two masses= radius of earth and shouldn't be confused with radius of a body of mass m.
Thus equating both forces if I'm not wrong
F1=F2; mg=Meg1, Me=m(g/g1)
Mass of the earth still varies in this way too.68.147.41.231 (talk) 05:36, 16 January 2011 (UTC)khattak#1-420[reply]
EDIT
Putting respective values of gs in both cases we get Me=Me w/o putting numerical values of g, G, r
Me = g r² / G= (GMe/r²)r²/G=Me
Similarly
Me = mg/g1=m(GMe/r²)/(Gm/r²)=Me
Mass of earth Me itself unknown in its equation of gravitational accelaration g = GMe/r² then how come we can get Me from equation Me = g r² / G.
For your first question: No. The in the formula must be measured at distance from the earth's center. If you move up into space, increases, but decreases such that your computed stays the same.
I'm not sure I understand your second question. –Henning Makholm (talk) 05:51, 16 January 2011 (UTC)[reply]
Note that the acceleration of gravity is something you can measure with simple mechanical experiments. Measuring the universal constant of gravity G is quite a bit harder; see torsion balance and gravitational constant for more details. –Henning Makholm (talk) 15:04, 17 January 2011 (UTC)[reply]
Does the 'center' in "on-center distance" between the Earth and Moon refer to their barycenter? The Moon's gravity does not change the Earth's mass, but there are changes in tidal forces (proportional to the inverse cube of distance) while gravity is proportional to the inverse square. ~AH1(TCU) 02:08, 18 January 2011 (UTC)[reply]
on-center OR center to center means the distance between the center of earth to the center of resting mass (may be of moon size) on earth.
As w = mg = m (MG/R^2) where R is radius of earth but actually the distance between center of earth to center of a resting mass on it. Here is how theoritically the weight of body decreases for the same mass due to increase in center to center distance between them.
1- Let a solid steel sphere of radius 100 m of mass m on earth
2- Let the same solid steel sphere remoulded to either hollow big shpere of thin shell or long vertical tube bar on earth.
The weight of a resting body of mass m on earth shown previously becomes zero when its size reaches to the size of earth exactly (if i'm not wrong)
The measurement of g through experiment is only useful for earth but not for the other celestial bodies 68.147.41.231 (talk) 07:18, 18 January 2011 (UTC)khattak#1-420[reply]
For planets that have moons, astronomical observations of how the moons move allows one to measure the acceleration of the moon directly. More careful observations of the orbits, including how the moons perturb each other away from pure Keplerian orbits, allow astronomers to calculate the masses of the moons themselves. The same technique must be used for planets that have no convenient moon to observe (Mercury and Venus). Later, of course, the orbits of artificial space probes that came close to those planets allowed more precise measurements.
Mass estimates for lone asteroids and trans-Neptunian objects tend to be very uncertain because there is nothing near them whose acceleration can be measured. –Henning Makholm (talk) 10:10, 18 January 2011 (UTC)[reply]
How are improved measurements of the speed of light reported?
Since the definition of the meter fixes the value of the speed of light at exactly 299,792,458 m/s, how are improved measurements of the speed of light reported? —Bkell (talk) 06:06, 16 January 2011 (UTC)[reply]
They become advances in metrology: more precise ways to measure length (in practice, that means more precise calibration of existing length measurement methods). –Henning Makholm (talk) 06:55, 16 January 2011 (UTC)[reply]
You just contradicted yourself - you said the speed of light is fixed, yet you ask how its accuracy is improved. A fixed value can't be improved, then it wouldn't be fixed. --Plasmic Physics (talk) 08:26, 16 January 2011 (UTC)[reply]
The definition defines the length of the metre in terms of the fixed, constant, speed of light, so a "measurement" of the speed of light is used to refine the measured length of the metre, to define the metre more accurately, as Henning said above. Dbfirs 09:30, 16 January 2011 (UTC)[reply]
Yes, I understand all of these things. But presumably there are still efforts to reduce the measurement uncertainty of the speed of light (or, to be technical, of the length of the meter). Simply defining the meter in the way we do doesn't mean we are suddenly disinterested in determining more and more precisely what the speed of light is—it just means we can no longer express the results of our experiments as more significant digits in a quantity expressed in meters per second. Surely there continue to be ever more precise apparatus built to determine the speed of light length of the meter. My question is, how are the results of those experiments reported in the literature? It's a literal question—what kinds of words and phrases are used? It used to be possible (in 1972) to say, "We have determined that the speed of light is 299,792,456.2±1.1 m/s," but that is meaningless now. And surely it is just as meaningless to say something like, "We have determined that the length of the meter is 1.00000000000046 m." So how is it done? —Bkell (talk) 10:42, 16 January 2011 (UTC)[reply]
Hmm, after thinking about Henning's answer a little bit, perhaps I see. Is it the case that, since the redefinition of the meter, attempts to more accurately determine the speed of light per se have ceased, and instead other things are just measured more precisely against the speed of light? So the results of these experiments, which would previously have been interpreted and reported as more precise measurements of the speed of light, are now interpreted and reported as more precise measurements of some other quantity? —Bkell (talk) 10:48, 16 January 2011 (UTC)[reply]
Yes, the redefinition enabled a more accurate determination of the length of the metre, currently realised using the wavelength of a particular design of helium-neon laser, accurate to almost eleven significant figures, whereas the previous "krypton" definition (in terms of which the speed of light was measured) was accurate to less than nine s.f. Each redefinition of the metre throughout its history didn't change its length, but increased the accuracy with which we can measure the original length (though each was actually based on the previous definition, not on the original seconds pendulum or the ten-millionth of the half-meridian). Dbfirs 11:13, 16 January 2011 (UTC)[reply]
The definition of the meter is a ratio that defines the meter not the speed of light. If the uncertainty in the speed of light is reduced in the future, it will create options to keep the present meter definition or to redefine it by a ratio with more significant figures. The article Speed of light mentions the CGPM standardisation conference that ratified the present standard and a future revision might proceed in a similar way. Cuddlyable3 (talk) 11:29, 16 January 2011 (UTC)[reply]
Any subsequent redefinitions will be better measurements of the length of the metre. There is absolutely no intention to ever change the current value of the speed of light from 299,792,458 m/s or to change the definition of the metre. I assume that this is what Cuddlyable3 was saying, but the reply could possibly be mis-read. Any improvements will just give a more accurate realisation of the metre. There is now zero uncertainty in the speed of light, but there is uncertainty in super-accurate measurements of the metre to eleven significant figures. The announcement will be something along the lines of "The new recommended realisation of the metre is now [xxxxxxxxxxxx ±yy] wavelengths of [a particularly stable and easily measurable laser light] (or other radiation in the E-M spectrum) under certain conditions" (e.g. in zero gravity). This will not change the length of the metre because it will be within the previous limits for realisation, but it will give accuracy of perhaps twelve significant figures. Dbfirs 13:18, 16 January 2011 (UTC)[reply]
Bkell, that's exactly correct. The experiments are the same either way; what changes is the language used to describe them. -- BenRG (talk) 21:27, 16 January 2011 (UTC)[reply]
Asking how the accuracy of the speed of light is improved, is like asking how the accuracy of the number zero is improved. The speed of light was made to be exactly the current number. The number zero will never be made more accurate to change from 0.0000 to 0.0001. --Plasmic Physics (talk) 04:17, 17 January 2011 (UTC)[reply]
No, you're missing the point. An improved accuracy of the knowledge of the speed of light means improving the accuracy of the knowledge of the size of the unit m/s. It's like the electronvolt: the energy required to move an electron through a voltage difference of 1 volt is 1 eV by definition, but if we measure this energy more precisely, it doesn't mean we know a more precise value for the constant 1; it means we know the size of the eV more precisely. In this case we would express this knowledge by stating the value of the eV in joules, say. The original poster asks how we would express an improved precision of the speed of light, since there isn't an alternative unit suitable to convert m/s into for this purpose. I don't know the answer. --Anonymous, 07:47 UTC, January 18, 2011.
I gave an example above of how the "improvement" might be expressed as an improved realisation (not definition) of the length of the metre. I don't see what the problem is. The second is known to a high degree of accuracy. The speed of light is fixed, so the only variable is the accuracy with which the metre is known. Dbfirs 10:47, 17 January 2011 (UTC)[reply]
Measuring the length of a meter may sound absurd, but that's what happens when length is a derived unit of time. But for example, if you happen to have an old platinum-iridium meter bar lying around in your attic, with improved interferometry equipment you might take it out for grins and see if it's a little longer or shorter than a meter. You might then of course use the same improved device on a bridge, space elevator, Moon probe, meridian from North Pole to the Equator through Paris etc. - improving your measurement of the length of the distance, whatever it might be, in each case. (Well, except the North Pole - is there a North Pole at the nanometer scale? I'd think every time the ocean currents shift or a billion Chinese commuters try to get to work or (at least) when the currents in the outer core shift with the magnetic pole, that it must move too much to measure precisely, but I may be wrong. Wnt (talk) 05:48, 19 January 2011 (UTC)[reply]
Yes, the problem with the original metre as determined by the seconds pendulum was that it varied according to where the measurement was done. The fraction of the meridian was actually mis-calculated, so there is no point in re-measuring. The prototype bars were improvements, especially when temperature was specified, but even these changed over time. I think the current definition is based on the "best" historic measurements of the latest bar, but it would be interesting to re-measure. I'm sure someone must have done this. Dbfirs 18:55, 19 January 2011 (UTC)[reply]
Hexafluoroethane and fluorine
Will hexafluoroethane react with fluorine? --84.61.131.41 (talk) 08:17, 16 January 2011 (UTC)[reply]
Possibly, under ultrviolet light, the hexafluoroethane may dissociate into trifluoromethyl radicals which would react with fluorine to produce tetrafluoromethane. --Plasmic Physics (talk) 08:26, 16 January 2011 (UTC)[reply]
Diesel passenger cars without diesel particulate filters
Why aren't there any diesel passenger cars without diesel particulate filters anymore available in the European Union? --84.61.131.41 (talk) 08:55, 16 January 2011 (UTC)[reply]
Have you read the obvious article Diesel particulate filter which gives the IMHO fairly obvious answer:
While particulate emissions from diesel engines were first regulated in the United States, similar regulations have also been adopted by the European Union, most Asian countries, and the rest of North and South America World List of Standards.
While no jurisdiction has made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all on-road diesel engines will be fitted with them. In the European Union, filters are expected to be necessary to meet Euro.VI heavy truck engine emissions regulations currently under discussion and planned for the 2012-2013 time frame. PSA Peugeot Citroën was the first company to make them standard fit on passenger cars in 2000, in anticipation of the future Euro V regulations.
Density is a function of mass and volume. Therefore, you can only measure density indirectly, having measured mass and volume beforehand.
Therefore, can we say that density is not a fundamental property of the universe? Can we say that it is a derived property?--Leptictidium (mt) 10:05, 16 January 2011 (UTC)[reply]
How do you define your term "fundamental property" ? Density can be measured directly - for example, a hydrometer measures the density of lqiuids. You could equally well argue that mass is derived from density and volume, or that volume is derived from density and mass. Gandalf61 (talk) 11:37, 16 January 2011 (UTC)[reply]
"Fundamental property of the Universe" is a very problematic term. Somewhat simpler is "fundamental property of a theory" - here it depends on what sort of system you look at (particle or fluid) and at what level you look at it (e.g. continuum approximation of a fluid vs. something like kinetic theory). If you talk about continuous systems, then density is the fundamental property and mass is derived by integrating over finite volumes. If you talk about particles, (particle) mass is fundamental and density is derived by averaging over finite volumes. --Wrongfilter (talk) 12:01, 16 January 2011 (UTC)[reply]
Is pH applicable to non-water solutions?
e.g., can pure ethanol have a pH? 75.4.194.121 (talk) 10:16, 16 January 2011 (UTC)[reply]
Not really, no. The way that pH is defined will only really work in dilute aqueous solutions. However you can (and people do) define an acidity function for non-aqueous solvents: these are practical the same as pH if the solvent is water, but are easier to extend to other solvent systems. Physchim62(talk) 13:13, 16 January 2011 (UTC)[reply]
Would it be proper to edit the lead of the pH article to say, "pH is a measure of the acidity or basicity of an aqueous solution? I would do it myself but I don't trust my knowledge of the matter. 75.4.194.121 (talk) 22:17, 16 January 2011 (UTC)[reply]
scratch that -- I will be bold and make the change, and if you disagree you can revert it :) 75.4.194.121 (talk) 22:18, 16 January 2011 (UTC)[reply]
Crap, I got reverted in less than ten minutes. OK, if the change is worth making, I leave the work to one of you. 75.4.194.121 (talk) 22:26, 16 January 2011 (UTC)[reply]
I think pH should apply to any solution that can produce hydrogen ions, such as sulfuric acid. After all, if you have a very concentrated solution of sulfuric acid (clouds of Venus, say), with maybe a little trace of water left, when do you say "well that tears it, no more pH measurements!" Wnt (talk) 05:53, 19 January 2011 (UTC)[reply]
(note, however, that p[H] is not precisely the same as pH, and the distinction is one of the more curious and obscure of chemistry's dark arts. Wnt (talk) 05:55, 19 January 2011 (UTC)[reply]
German dioxine contamination: how long does food take to pass through retail system?
How long does it take chicken, eggs, and pork to pass through the retail food system. If it is slaughtered or laid on Day 1, how long is it before it is all sold or disposed of? I imagine the figure is different for fresh, frozen, tinned, or otherwise processed food.
I know the dioxin is said to be very diluted by now, but the thought of food being possibly contaminated takes all the pleasure away from eating it. My local supermarket has large quantities of cakes being sold at reduced prices, so other people feel the same. Thanks 92.29.122.203 (talk) 10:45, 16 January 2011 (UTC)[reply]
For fresh egg this might be less than 10 days, but for deep frozen pork products or sausages this might be weeks or even months.--Stone (talk) 13:43, 16 January 2011 (UTC)[reply]
Image identification
Can someone identify these? Doesn't have to be species name, anything will help :)--Abhishek Jacob (talk) 12:58, 16 January 2011 (UTC)[reply]
As I'm pretty good with herpetology I felt I should identify the second picture at least :)
Looked vaguely like a Wood Frog at first, but I checked the file description and it was found in India. Given our coverage of Indian frogs is all stubs, the exact species probably won't be clear, but I think I can narrow down the classification to a member of the Ranidae. Crimsonraptor | (Contact me)Dumpster dive if you must 13:24, 16 January 2011 (UTC)[reply]
FYI, they were all taken from my home in Palakkad, Kerala, India. Coordinates: 10°45'39"N 76°38'25"E --Abhishek Jacob (talk) 14:17, 16 January 2011 (UTC)[reply]
Bug Guide is very good resource but unfortunately is strictly North American arthropods. The 5-part antennae suggest hemipteran to me. The lack of wings suggests either a nymph or a ground beetle. Do you have a ventral image that displays the mouthparts? That would clear things up significantly. -Craig Pemberton 06:38, 17 January 2011 (UTC)[reply]
Also, the time of year and a cross section of the mushrooms or at least an image of the gill attachment would be very helpful. -Craig Pemberton 06:44, 17 January 2011 (UTC)[reply]
can human beings destroy life on earth?
I'm asking this because I hear such sentences a lot.but I think it is somehow impossible, because:
1.There are many extremophile forms of life in places that are somehow less affected by human activities, such as some caves,black smokers in deep oceans,etc.
2. we rely on other living things to live on, so before destroying other living things, we will die out. ( and therefore we won't be able to kill other things.)
3.Life (although very slowly) is adapting itself to some human made environment(or materials).the nylon eating bacteria, for example.
4. there is probably no one who intends to destroy life,I mean some people may not care about the environment,but they don't realy mean to destroy it.
I'm not neglecting the importance of taking care of the environment.but can human beingd destroy life in a way it can't recover itself again?--Sina-chemo (talk) 16:49, 16 January 2011 (UTC)[reply]
A cobalt bomb could theoretically move cockroaches to the top of the food chain. More info about these devices on Doomsday device. Do you ever suffer from happy thoughts?--Aspro (talk) 17:07, 16 January 2011 (UTC)[reply]
Right now? No. We can't. We can't even kill all the humans, much less all life. A Cobalt bomb would not work either - we don't have enough nukes to kill all humans using it. Ariel. (talk) 21:12, 16 January 2011 (UTC)[reply]
Though one should not neglect the fact that we could potentially make the world poisonous enough with such weapons as to make life pretty dang miserable, and to kill off a good percentage of people. Even a nuclear exchange between, say, just India and Pakistan would have global climate consequences, which would have severe global health consequences as well. That being said, it would be very hard to reliably kill off all humans with nuclear weapons. If I were a mad scientist, I would invest in infectious diseases, instead. You'd miss people who lived out of contact with other people, but you'd be able to kill off a massive number of people very quickly if you had the right pathogen. --Mr.98 (talk) 21:30, 16 January 2011 (UTC)[reply]
The key word, of course, is reliably. If you're a Vogon captain with a contract to destroy all human life on Earth, you can't be sure of fulfilling your obligations by setting off enough weapons to induce nuclear winter, partly because we don't know whether the models that predict it are correct. If you actually prefer not to extinguish humanity, it's probably an experiment you don't want to run. Even if, like me, you think the precautionary principle in general is a bunch of technophobe hogwash. --Trovatore (talk) 23:32, 16 January 2011 (UTC)[reply]
Although if you are a Vogon captain, you may have better models Nil Einne (talk) 00:03, 17 January 2011 (UTC)[reply]
or in any case better poetry --Trovatore (talk) 00:04, 17 January 2011 (UTC) [reply]
well, unless vaporized a la the Vogons, something is sure to survive no matter what we do to the planet, and whatever it is that is left will someday evolve to intelligent life, again. PЄTЄRS J VЄСRUМВА ►TALK 00:34, 17 January 2011 (UTC)[reply]
I expect nuclear winter would kill more people than a bioweapon. You can't find a cure for nuclear winter, you just have to try and endure it for a few years (which could only be done by reasonably small groups because of the need for food). It is possible someone would find a cure for a bioweapon. It would be very difficult to guarantee that everyone would die, though. It would be impossible to get even close to killing all life on Earth. --Tango (talk) 23:40, 16 January 2011 (UTC)[reply]
It would be very difficult. The energy involved would be enormous. Even moving small asteroids enough to move them out of a collision course with Earth is at the limit of our abilities (I expect we could do it if we really needed to and spotted the asteroid long enough in advance). --Tango (talk) 23:40, 16 January 2011 (UTC)[reply]
I've read that an economical way to do this is by changing the course of smaller asteroids and let them move past or collide with the larger asteroid we're interested in. An extreme example was given in this paper (section 4.4). Here it is suggested that we should use asteroids to change the Earth's orbit to prevent it from being destroyed by the Sun. Count Iblis (talk) 23:55, 16 January 2011 (UTC)[reply]
Alternatively, we could use the method suggested in that paper to move the Earth closer to the Sun... Count Iblis (talk) 00:09, 17 January 2011 (UTC)[reply]
Runaway climate change offers a plausible option, though most authorities do not believe that it could reach Venus-like proportions. The key threshold of boiling the oceans and create water vapor as a greenhouse gas seems out of reach. Still, the Sun gets hotter all the time, and if we manage to put enough methane into the atmosphere abruptly (clathrate gun hypothesis, arctic methane release) we might find out for sure. Wnt (talk) 01:51, 17 January 2011 (UTC)[reply]
but we don't realy want to destroy the planet or life.Can i conclude that if we continue polluting the planet as we are now, Life won't disapear?I'm not saying that we are allowed to pollute the environment. but if we do, we will die out first, so there would be no one to continue polluting it. — Preceding unsigned comment added by Sina-chemo (talk • contribs) 05:54, 17 January 2011 (UTC)[reply]
No: Even if we pollute far more than we are now, life won't disappear, the more fragile creatures will die out, but the rest will adapt. And even if we pollute to the point that everything dies, we would be the last to die, since unlike them we can do something about it. And finally it won't happen, the peak for pollution on earth was years ago, it's only getting better from here. China and India have lots of work to do, but I expect an environmental revolution within the next generation. Ariel. (talk) 06:15, 17 January 2011 (UTC)[reply]
We would certainly not be the last to die - plenty of bacteria will survive longer. If nowhere else, then at least inside the corpse of the last human, but likely much longer in places like the deep hot biosphere. The claim that "pollution" is somewhat lower now than in its heyday is not implausible, but that depends very much on what you count as pollution. CO2 emissions are at (or near, due to minor fluctuations) an all-time high, and CO2 accumulates in the atmosphere, so CO2 levels are rising fast. --Stephan Schulz (talk) 08:10, 17 January 2011 (UTC)[reply]
We probably couldn't destroy all life but we could reduce it to extremophiles. If we put all our efforts into it, we could set up a sort of curtain between the Earth and Sun, blocking enough light to rather quickly produce a transition to a Snowball Earth state, in which the oceans would freeze over and the entire surface would resemble Antarctica. There would still probably be some life at deep-ocean vents, but that would probably be all. Looie496 (talk) 18:42, 17 January 2011 (UTC)[reply]
A true Venus-style runaway greenhouse would be a thorough steam-cleaning all the way down to the core. There would be no liquid water left, though it would take a while. Wnt (talk) 22:10, 17 January 2011 (UTC)[reply]
I am reminded of this website discussing ways to really and truly destroy the Earth, which would presumably destroy all life on it as well. Most of their methods are ridiculously impractical and completely unachievable, but it is an interesting idea to think about. For example, if you can find or make a black hole, that would potentially do a very good job of exterminating the Earth (and everything on it). Dragons flight (talk) 20:51, 17 January 2011 (UTC)[reply]
Even the worst mass extinctions that wiped out 90% of all species failed to destroy all life on Earth, especially prokaryotes which have more rapid microbe evolution capabilities, and life always recovers due to filling of niches by new species. However, even without "intending" to cause a mass extinction, the law of unintended consequences means that we may accomplish just that through environmental degradation (including business as usual scenarios). Even a Snowball Earth could have larger organisms that survive in warmer ocean pockets, likewise at Europa (purely hypothetical). The food web is an "interconnected system", meaning that the loss of one species could affect many others. A related fact is that mycorrhizae are threatened by environmental change, for example through plant biodiversity effects. Rapid global warming from anthropogenic causes could create novel biomes, leaving non-migratory species in new climates and vegetation patterns that in turn are slow to respond to rapid directional selection. Although the aforementioned mechanisms would not destroy all life, positive feedbacks could continue the trend well past the end of the initial "forcing", and ozone depletion would irridiate most complex life. Even an impact event that causes the crust to break and bring magma to the surface, as the Chicxulub crater impactor likely did would still not be enough to cause the extinction of all lifeforms. Some technological mishap such as grey goo might do it, however. ~AH1(TCU) 01:58, 18 January 2011 (UTC)[reply]
Genesplicing has the potential to wipe out any particular plant or animal by presenting some lethal pest. Mad scientists are at the early stages of splicing bits of DNA into the genomes of mice, goats, insects and bacteria. The intended consequences have included making goats produce spider silk precursors in their milk, making mice glow in the dark or have human brain cells, and encoding computerized information in the genomes of E coli. One day, such an experiment might make a germ vastly more lethal than its natural form, or might cause a pest such as venomous insects to become a lethal scourge. An agricultural pest might devastate staple food crops and cause widespread starvation. Military weaponization of disease organisms has horrible potential to wipe out humanity. Just as a billion monkeys might type out "Hamlet," a thousand biolabs tinkering with genomes might unleash selfperpetuationg and unstoppable havoc, with greater damage potential than one superbomb going off. Its easy to envision a bioexperiment going wrong in a way which might leave some lifeforms on Earth, but without vertebrates. I have seen something as simple as mosquitoes with naturally occurring West Nile destroy all birds in a large area. Fortunately the mosquitoes had limits to their range. Edison (talk) 17:41, 18 January 2011 (UTC)[reply]
This would seem to be true, not just for human experimenters but also the febrile imagination of Nature, but yet... so many of the great mass extinctions are explained not by disease but by some crude physical factor, that it makes me doubt the power of disease to finish such a task. Most of the genome is known to take a day off in someone or another - even those which appear "lethal" in mutants have only been proven to be lethal in one particular strain (or two, or three) under certain conditions. You can have a very nasty war indeed with bioweapons, but someone will probably live to write the history. Wnt (talk) 05:59, 19 January 2011 (UTC)[reply]
Massive spring
If a spring with mass is pulled on both ends with different forces, by how much will the spring extend? 74.15.137.130 (talk) 16:50, 16 January 2011 (UTC)[reply]
It doesn't matter if the force is applied at both ends, or just the one end. Simply add (strictly it's subtract, due to opposite directions) the forces, and apply Hooke's law, if the spring is purely elastic. CS Miller (talk) 17:35, 16 January 2011 (UTC)[reply]
The force has to be the same size in both directions; otherwise, due to Newton's second law, the entire spring will start moving in the direction of the greatest force. One certainly shouldn't add or subtract the measurements from the two ends; at equilibrium it's the same force just measured at different places. And it only counts once in Hooke's law. –Henning Makholm (talk) 17:58, 16 January 2011 (UTC)[reply]
I know it would accelerate, but it would also stretch. How much would it stretch by? Suppose the spring was 1kg, with an outward force of 10N on one end and an outward force of 5N on the other. It would accelerate by 5m/s^2. If I understood Csmiller, it would stretch by 15N/k, right? If so, why? 74.15.137.130 (talk) 19:29, 16 January 2011 (UTC)[reply]
No, the situation is slightly more complex than that. Initially, one end of the spring will accelerate faster than the other until "accelerating equilibrium" (not a standard term) is reached. To determine both acceleration and extension, you need to be given the mass and the spring constant (often denoted λ in Hooke's law). Are you wanting to find both the extension and the acceleration? If we assume that the spring is uniform, then, once the two ends are accelerating at the same rate and oscillations have been damped out, the tension and thus the proportional extension (stretch) will increase linearly from the 5N end to the 10N end, but you can just use the average tension (7.5N) in Hookes law to give the total extension. Dbfirs 20:48, 16 January 2011 (UTC)[reply]
Thanks, but I have a few more questions (sorry!). First, is there a way to derive the average tension rule? Secondly, my textbook said that if a massive spring attached to a wall is stretched by a force F, the extension x will equal F/k. If I've understood things, this would only be true if the spring were static, right? Finally, if the same spring (attached to the wall) were connected to a mass, what would the total potential energy be? My textbook said that it's still (1/2)kx^2, but why would that be? I would think it would be (1/2)k(x/2)^2, because x/2 is the change in distance between the center of masses of the spring and the mass. It also assumed that the mass of the spring << the mass of the mass...would a more general case change the answer? Thanks! 74.15.137.130 (talk) 21:15, 16 January 2011 (UTC)[reply]
It should be easy to derive the "average tension rule" by considering forces on a small element δy of the spring and integrating, but I haven't thought through the exact method. Yes, the spring would be static if it is attached to a static wall and the free end is not moving. To answer your last question, you need to distinguish between potential energy stored in the spring and gravitational potential energy. It is not clear from your question exactly how the mass is attached, but the energy stored in the spring depends only on the extension, not on any attached masses. Dbfirs 21:56, 16 January 2011 (UTC)[reply]
By my second question, I meant that the extension was instantaneously x...would this only equal F/k if the spring were static (ie the end were not moving)? As for the last question, I'm sorry for the ambiguity but I had meant a spring-mass system that was horizontal (so no gravitational PE). To clarify my question...if a mass is subjected to a Hooke's Law force, its potential energy would be -∫-kxdx = (1/2)kx^2. But that only takes into account the energy of the moving mass. For a two-body system, the total potential energy would be -∫F(r)dr, where dr is the distance between the center of masses of the two bodies. So, shouldn't the potential energy be (1/2)k(x/2)^2? (x/2 being the distance between the COMs in terms of the extension x)74.15.137.130 (talk) 22:24, 16 January 2011 (UTC)[reply]
To solve that problem imagine that your spring is made of N small springs attached in series each one with a mass m_i = m/N and a spring constant k_i = kN. If the forces applied at either end of the whole spring are F_0 and F_N, and we define F_i as the force between the spring i and the spring (i+1) than we have F_i = F_0 + (i/N)(F_N-F_0) because that way all little springs will have the same acceleration. For a large N (-> infinity) The forces F_(i-1) and F_i acting on either and of the spring i will be almost the same and then it makes sense to use their average as an expression for the tension T_i on that spring: T_i = (1/2)(F_(i-1)+F_i) = F_0 + ((i-1) + i)/2N) (F_N - F_0) = F_i = F_0 + ((i-1/2)/N)(F_N-F_0). The spring i will stretch by an amount x_i given by x_i = T_i/k_i = 1/(kN) [F_0 + ((i-1/2)/N)(F_N-F_0)] = F_0(N-i+1/2)/(kN^2) + F_N(i-1/2)/(kN^2) and the total stretch x is given by x = SUM_(i=1)^N x_i = F_0/kN^2 SUM_(i=1)^N (N-i+1/2) + F_N/kN^2 SUM_(i=1)^N (i-1/2) = F_0/kN^2 (N^2 - N/2(N+1) + N/2) + F_N/kN^2 (N/2(N+1) - N/2) = k/2(F_0 + F_N). Conclusion: Use the average force 1/2(F_0 + F_N). Dauto (talk) 23:06, 16 January 2011 (UTC)[reply]
Nice! Can you also illuminate the potential energy issue (or let me know if I'm not explaining myself clearly)? 74.15.137.130 (talk) 00:26, 17 January 2011 (UTC)[reply]
I'm not clear what type of potential energy you are considering. Moving masses have kinetic energy, not potential (other than gravitational), and the spring potential energy is stored in the spring, not in the "mass". If a mass is attached to the spring, it is usually better to consider two separate springs. (My thanks to Dauto for setting out clearly what I was half-thinking.) You should be aware that the formula for energy stored in a spring is derived assuming that the tension and extension are uniform throughout the length. It will need to be modified (along the lines of Dauto's method) for an accelerating spring when the extension per unit length is not uniform. Dbfirs 10:30, 17 January 2011 (UTC)[reply]
I get V = [3F_0*F_N + (F_N-F_0)^2]/(6k). Dauto (talk) 20:29, 17 January 2011 (UTC)[reply]
I'm sorry for being persistent, but how did you get this expression? And why, in your previous derivation, does "it make sense to use the average force as the tension" for a small spring? 74.15.137.130 (talk) 05:41, 18 January 2011 (UTC)[reply]
When N -> infinity the difference between the two forces acting on either end of the microscopic string element becomes negligible F_i - F_(i-1) = (F_N - F_0)/N -> zero. So you can use either one of them or their average and it will give you the same results. My choice makes the algebra slightly easier and that's why I chose it. I don't have time right now to post my solution for the potential energy. I will try to come back to it later. Dauto (talk) 16:05, 18 January 2011 (UTC)[reply]
Makara Jyothi star
Hi. Using Yoursky, I tried to identify the Makara Jyothi star that would have been seen on January 14 at Sabarimala. Since the "star", if it is a star, sets just after sunset, the actual star should set around that time (prior to 8 pm local time, or 14:30 UTC). The only two candidate stars I found that were bright enough and set in the general direction of west were Altair and Deneb. Since Altair set very close to sunset, and could only be seen in bright twillight, the star would probably be Deneb. This star sets around the same time that the stampede occurred, meaning it would likely disappear from the local horizon just before the disastrous incident, since the area is quite mountanous, and the star would appear to graze the horizon. However, it would require a program such as Stellarium to verify the exact setting time from the exact location. Is Deneb a likely candidate for this star, often called a "celestial event" by pilgrims? Thanks. ~AH1(TCU) 16:59, 16 January 2011 (UTC)[reply]
Sirius is known as Makarajyothi. But that's not what the pilgrims want to see. A light appears three times on top of the nearby mountain, known as Makaravilakku, which is actually lit by government officials but believed to be divine by the pilgrims.--Abhishek Jacob (talk) 19:12, 16 January 2011 (UTC)[reply]
Cardiac pressure-volume loop
Can someone explain to me how the cardiac pressure-pressure volume loop can work without violating Boyle's law? I'm just not sure to understand how, with all valves closed, the ventricle can increase/decrease pressure without changing its volume. This would be the 2 vertical sections of the chart.
Boyle's law applies to gases and other compressible fluids. Blood is incompressible so you can increase the pressure by squeezing without changing the volume. (Pedantic note: Nothing is actually incompressible, so the volume does actually change, but by such a small amount you can ignore it.) Ariel. (talk) 21:18, 16 January 2011 (UTC)[reply]
Evolution of poison dart frogs
I was watching this video http://www.youtube.com/watch?v=vxjc8m6s2p0 where they talked about the evolution of poison dart frogs. My question is how did they evolve the brightly colored patterns? A few points come to mind.
1) The poison secreted depends on their diet, when their diet is taken away they do not produce poison.
2) The coloration is independent of their ability to secrete poison. In other words, being brightly colored doesn't mean it's able to secrete poison.
3) Presumably they evolved from normal colored frogs, green, brown, grey, etc. Early in its evolution there were probably normal colored frogs that also secreted poison. Why would there be a selective advantage to being brightly colored over being normal colored if they both secrete poison? Wouldn't the predators be dissuaded from eating frogs in general if they became sick and died from eating frogs? If there were both dull and bright colored frogs that secreted poison, the bright colored frogs would stand out more. My only hypothesis is that the dull colored frogs would be harder to identify as a danger if it blends in more to its surroundings, but wouldn't that also be an advantage? Camouflage is a selective trait since it's harder to spot and eat.
So my question is what selected for brightly colored frogs, while dull colored frogs which ate the same diet and should secrete the same poison, were not selected for? ScienceApe (talk) 20:21, 16 January 2011 (UTC)[reply]
(edit conflict)My only guess would be that if all the frogs were the same dull green and whatnot, a poisonous frog could easily be mistaken for a non-poisonous frog. A predator, not knowing the difference, would perhaps try to eat the dart frog (possibly killing both in the process.) Simply, the colorations help the frogs' enemies distinguish it from other "safer" frogs to eat.[original research?] Like I said, though, merely a guess. :) Avicennasis @ 21:22, 11 Shevat 5771 / 16 January 2011 (UTC)
This is a textbook case of warning coloration, which can arise independently of the source of toxicity. Note that mimicry can result in similar warning colors on non-poisonous species. SemanticMantis (talk) 22:36, 16 January 2011 (UTC)[reply]
It must be all about the other frogs, the ones which are good to eat. If toxic frogs made up a large proportion of frogkind, I think you would be right - their coloration would serve no purpose; looking like a frog (an exaggerated frog?) would be sufficient. When their toxicity was just starting to evolve, though, the toxic ones were few. (Seems likely that they still are, among South American frogs in general.) Being toxic on its own wouldn't do them much good, since for predators the tiny risk of being poisoned might not outweigh the great benefit of eating mostly harmless frogs. Being toxic and slightly distinctive, though, to push the predators onto the other frogs, is an enormously successful strategy, which quickly leads to being brightly colored. (This might be accelerated by coevolution with the predator's instinct to dislike the brightly colored ones, if the predator has such an instinct.) 213.122.1.222 (talk) 00:02, 17 January 2011 (UTC)[reply]
Bear in mind that a frog which is non-poisonous due to its diet can still have a winning strategy as a Batesian mimic of its poisonous comrades. Since a predator eats many frogs and is not allowed any mistakes, I imagine that even a few poisonous members of the species cast a very long shadow. Wnt (talk) 01:36, 17 January 2011 (UTC)[reply]
Based on natural selection and predators that preyed on ancestral species of poison dart frogs, the species that did have bright colouration AND poison likely had a survival advantage over those that did not and were subsequently eaten, while camoflage and warning colours often co-compete to improve survival. Mimicry of existing poisonous species such as by the Viceroy butterfly also provides a similar advantage. ~AH1(TCU) 01:34, 18 January 2011 (UTC)[reply]
Medical question
Is my hair more likely to fall of if I wear a baseball hat? A lot of people say so, but to me it doesnt make a lot of sense... --92.244.158.89 (talk) 21:21, 16 January 2011 (UTC)[reply]
I think some hairs will come off due to the rubbing of the hat on your scalp, dislodging some hairs. However, I doubt it would really be anything significant. --T H F S W (T·C·E) 22:21, 16 January 2011 (UTC)[reply]
While this may be a myth, hats do cause hair breakage and, to a lesser degree, split ends. Since hats are not washed as frequently as other clothing, they can also lead to scalp uncleanliness and possible Pityrosporum ovale contamination in men with naturally oily scalps. Some scalp infections, if left untreated, can cause hair loss.Bielle (talk) 22:28, 16 January 2011 (UTC)[reply]
I quite often wear a baseball cap when I'm out in the sun, but that's because most of my hair has already fallen out. HiLo48 (talk) 23:26, 16 January 2011 (UTC)[reply]
The quote from the article sounds suspiciously like a bit of original research at the Wikipedia end. It seems to imply, for example, that people with dandruff are more likely to develop baldness.
Now as for how hats could cause baldness, I should note PMID8628793, which finds "a relative microvascular insufficiency to regions of the scalp that lose hair in male pattern baldness". Since this concerns blood flow in the scalp, which might be interfered with by a tight hat, I think the old wives may win the science award on this one. Wnt (talk) 01:33, 17 January 2011 (UTC)[reply]
I had an idea in a dream Friday to make a Feynman diagram illustration of Keats's Ode to a Grecian Urn's most famous couplet. The preliminary result (which turned out amazingly better than I expected) is a weak interaction of bottom-down and top-down-up[3]. I'm wondering if someone might be willing to double-check the physics (my particle knowledge is terrible), and also maybe have a suggestion for a strong-mediated interaction that I can use as well, just because the coily gluon line looks neat. The only conditions are: a bottom quark becomes a top quark (Beauty is Truth), and the end products include a top-bottom meson (Truth Beauty). SamuelRiv (talk) 23:18, 16 January 2011 (UTC)[reply]
As far as the physics goes, unfortunately the baryon dut doesn't really exist because the quark t is too unstable and decays before it has enough time to form any bound states, and off course the bottom quark wouldn't back-decay into the top quark. But clearly those are minor points since you are not trying to describe a true physical process. Dauto (talk) 03:54, 17 January 2011 (UTC)[reply]
January 17
Suffocation
Why did humans evolve to feel pain from abnormally high CO2 levels, rather than abnormally low O2? Unlike the former, the latter would allow people to avoid going into areas with high N2 and little or no O2 (nitrogen asphyxiation) --75.15.161.185 (talk) 02:55, 17 January 2011 (UTC)[reply]
How often did early humans found themselves in such conditions throughout their evolution? Dauto (talk) 03:33, 17 January 2011 (UTC)[reply]
You might find the articles on Carotid body and hypoxia interesting. I think the answer is that we didn't really evolve a mechanism to detect low Oxygen levels, but CO2 is actually toxic, so it was much easier to evolve a mechanism to detect high levels of it. Keep in mind that it is incorrect to assume that EVERY single trait or mechanism is evolved for fitness. There are a lot of traits or mechanisms which are evolved sympathetically or inversely due to another trait which is evolved for fitness. For a very basic example, why aren't antelope legs thicker and stronger and less prone to breakage? Because longer and leaner legs are better at running. In the same way, why did we evolve that CO2 will kill us in the first place? Obviously, we didn't, it's just the result of us evolving to breathe oxygen. Vespine (talk) 03:54, 17 January 2011 (UTC)[reply]
And where on earth do you naturally get an extra high nitrogen level? The only likely place with low oxygen is high altitudes, which are usually very cold too, so no extra protective measures are needed. Graeme Bartlett (talk) 04:03, 17 January 2011 (UTC)[reply]
In electronics compartments near anything highly flammable. Many people have died when they go into a compartment to repair electronics without first venting the N2 and adding O2. --75.15.161.185 (talk) 04:08, 17 January 2011 (UTC)[reply]
I suspect that Graeme meant naturally occurring places. Sure, modern humans can create unusual atmospheres, but in order for low oxygen levels to have been an important evolutionary pressure for our species, our ancestors would have had to encounter low oxygen levels with some reasonable frequency. However, the presence of low oxygen levels (without also having high CO2 levels) would seem to be a very rare condition in the natural environment, and hence not something that humans would be expected to have evolved a response to. Dragons flight (talk) 04:13, 17 January 2011 (UTC)[reply]
It should be noted that large amounts of carbon dioxide actually form carbonic acid when dissolved in water; thus the carbon dioxide literally tends to create acidosis of the blood. This is a very large perturbation of body chemistry, and the body's response to it really is not all that impressive. To consider how much further evolution could go with such things, consider that mosquitoes are able to smell carbon dioxide and follow it for about 100 feet to their victims - despite, of course, producing it themselves! Wnt (talk) 08:47, 17 January 2011 (UTC)[reply]
according to our articles both Carotid bodies and aortic bodies primarily detect O2, not pH or CO2. So the answer is we already do detect it. Rmhermen (talk) 16:47, 17 January 2011 (UTC)[reply]
As a rule – or at least as a rule of thumb – we mammals are utter crap at evolving new signalling and sensing pathways because we just don't run through generations fast enough. We can tinker with existing pathways and mechanisms, but developing 'new' sensors is improbable virtually to the point of impossibility. So is there anything in our biological heritage that includes a tropic response to nitrogen gas? Even more broadly, are there any organisms known which respond actively to concentrations of nitrogen? (I don't count dying/not dying a a 'response' here.) Motile microbes which will move up or down a nitrogen concentration gradient, for instance? TenOfAllTrades(talk) 15:31, 17 January 2011 (UTC)[reply]
It seems unlikely, given that nitrogen makes up the bulk of the atmosphere. It's hard to do a definitive search, though, because sensors for fixed nitrogen are very common, and I can't think of a way to set up a search that filters them out reliably. (The bacterial systems that fix nitrogen could be thought of as nitrogen gas sensors, but I expect that they always operate at saturation under normal conditions.) Looie496 (talk) 18:32, 17 January 2011 (UTC)[reply]
Evolution often finds solutions that are merely "good enough". Detecting lack of oxygen rather than excess CO2 would be better, but it would be very rare that it would actually make a difference to reproductive success. Also, you wouldn't want to lose the ability to detect excess CO2 because there are situations where you get a CO2 build up without a significant drop of oxygen levels (too many people in an enclosed place, dissolved CO2 in a lake suddenly coming out of solution (see Limnic eruption), etc.). That means you would need both abilities, which is a drain on resources. Being able to detect a lack of oxygen may not be worth the cost. --Tango (talk) 19:26, 17 January 2011 (UTC)[reply]
I think that bats, bloodhounds, and star-nosed moles would each disagree with you in their own special way. While it seems like some mammals are "terminally differentiated", reproducing too slowly to evolve quickly or even to prevent losses of useful little things like vitamin C from the genome, we yet see that some of the longest-lived mammals somehow evolved rapidly in form and function to become humans, which was one of evolution's more curious accomplishments. And of course there remains a vast pool of various little shrewlike things that outnumber all the rest of us, just waiting to start down some new evolutionary path and claim a new place in the limelight. (Oh, and note the comment about O2 and the carotid body above) Wnt (talk) 22:03, 17 January 2011 (UTC)[reply]
Detecting N2 directly would be very difficult/impossible because it is non-polar which means it is difficult for any other molecules to grab hold of, after all, this is why there is so much of it in the atmosphere, because it doesn't react with anything. For species that fix nitrogen using nitrogenase, there is no need to have a tropism to it because N2 is everywhere. SmartSE (talk) 00:49, 18 January 2011 (UTC)[reply]
Well, as I wrote above, your own answer explains how it could be done: to build a biological N2 detector, all you would have to do is couple nitrogenase to a detector for fixed nitrogen, of which there are many examples. But as you also say, such a thing would be useless, because N2 is everywhere. Looie496 (talk) 22:07, 18 January 2011 (UTC)[reply]
Future space journeys
in future the man will find better ways for solve weightloss problem in space jurnays . i forcast that this mystry is hidden in comets
and sattlite and space craft groups will have diffrent missions . we will find severel mystrys of planets and moons with particle sending method that i want to publish . i have good ideas for this. a. mohammadzade — Preceding unsigned comment added by A.mohammadzade (talk • contribs) 05:02, 17 January 2011 (UTC)[reply]
Hello, I'm guessing English isn't your first language so apologies if there is a question there which I'm not seeing. The reference desk is for people who seek referenced answers to specific questions relating to science. Do you have a question? Vespine (talk) 05:43, 17 January 2011 (UTC)[reply]
that is so ,my mother toungh is turkish ,so i have some difficultys in english . I have write my special questions about solar system
last jan 11 under the subject "any one with new ideas for creation theories of solar system "wich shows my new theory upgrading from new explanation of objects and planets belts and astroids in solar system .
I wrote them not to find replays but for showing nessesity for development and changing in thus theories A.mohammadzade jan 18 iran—Preceding unsigned comment added by 78.38.28.3 (talk) 04:03, 18 January 2011
Do you need a dictionary? Here: Electromagnet. Or is this a homework question? Ariel. (talk) 11:03, 17 January 2011 (UTC)[reply]
Bread
What are the health problems from eating stale whole wheat or seed bread? If there is no mold on it and it was in the fridge? --41.213.125.249 (talk) 10:40, 17 January 2011 (UTC)[reply]
Why should there be health problems? Even if there was mold on it it would probably be harmless (most, but not all, molds are harmless when eaten (as opposed to inhaled)). What do you mean by "seed bread" - all bread is made from seeds. Ariel. (talk) 11:00, 17 January 2011 (UTC)[reply]
The term probably refers to Whole grain bread. It may also refer to Seed cake. Not sure which the OP means. Regarding health effects, presuming that there isn't any alergic concerns (i.e. you wouldn't have negative health effects from eating it fresh) and it isn't rotten or spoiled (as the OP says, no mold) then stale bread is just "dried out", i.e. slightly less water than fresh bread. I would say that such bread is perfectly safe, again with the caveats that there is no spoilage and there is no allergy concerns. --Jayron32 13:59, 17 January 2011 (UTC)[reply]
I regularly eat soda-bread which contains sunflower seeds, linseeds and sesame seeds. Maybe something like this is what the OP is referring to. I agree that there are few health risks in eating stale bread, with or without seeds. Our stale bread (not the soda bread) is made into breadcrumbs for use in other dishes. I'm still here! Oops, sorry that's WP:OR. Richard Avery (talk) 14:16, 17 January 2011 (UTC)[reply]
Rye bread and other breads infected by fungus could historically result in Ergotism. ~AH1(TCU) 01:23, 18 January 2011 (UTC)[reply]
gastric acid
do all other animals use HCl in their stomach as we do? — Preceding unsigned comment added by Sina-chemo (talk • contribs) 11:09, 17 January 2011 (UTC)[reply]
Yes, it does seem so (although I can't say with 100% certainty). Chlorine is very common in the environment - from ordinary salt, so it gets used as the acid plus when it's time to neutralize the acid it makes ordinary salt, and salt is used for other things as well (sodium is the main driver in nerves). However not all animals have stomach acid, acid breakdown is not the only form of digestion. Ariel. (talk) 11:52, 17 January 2011 (UTC)[reply]
No: In most insects, midgut pH is either mildly acidic or neutral. Lepidopteran and trichopteran larvae, scarabaeid beetles, and nematoceran flies have alkaline midguts, .... --Sean 15:27, 17 January 2011 (UTC)[reply]
Your reference to the midgut confuses the issue -- humans also have basic midguts. HCl is secreted in the stomach, but bicarbonate is secreted from the pancreas, and a look at our midgut and foregut articles seems to establish the change of foregut to midgut at the point of fusion with the bile duct -- looking at the bile duct article reveals that this duct meets with the pancreatic duct and enters the duodenum at the ampulla of Vater. Thus, insects are hardly unique in having basic midguts -- I'd say humans and most mammals do to. DRosenbach(Talk | Contribs) 19:17, 17 January 2011 (UTC)[reply]
e/c Any context? Can't find anything about it on Wikipedia, but it appears to be a product name by the Sterling (Kohler) plumbing company for a range of bathroom and kitchen products: see [4]. --jjron (talk) 17:48, 17 January 2011 (UTC)[reply]
" Vikrell is a solid composite material made of resins, fiberglass and filler that is exclusive to Kohler Company." [5] (See "shower stalls FAQs" box at bottom right of page). It apparently has integral pigment rather than a paint-like top layer, hence chips don't show. 81.131.68.227 (talk) 17:52, 17 January 2011 (UTC)[reply]
Are there any chemical compounds which are gaseous at STP, despite containing no chemical element which is gaseous at STP? --84.61.155.161 (talk) 17:37, 17 January 2011 (UTC)[reply]
Sulfur dibromide doesn't exist at STP. The next nearest I can find is boron tribromide (b.p. 91.3 °C, 196 °F). Physchim62(talk) 12:19, 18 January 2011 (UTC)[reply]
Citric acid in fruit
My family has been kicking around a recipe for corn cob jelly, and our most recent attempt at making it was somewhat of a flop. According to the package, pectin requires acid to work, and the typical way of doing this is to add lemon juice. The problem is that corn cobs don't make for a very strong flavor and the end product was rather more lemon-tasting than I'd like. Other than laboratory supply of citric acid (or hydrochloric for that matter!) is there a source of food-grade acid that isn't quite as strong a flavor as lemon juice? I was thinking vinegar, but that's unlikely to work well with a sweet product like a jelly. SDY (talk) 20:16, 17 January 2011 (UTC)[reply]
I don't know where you live but in NZ you can buy citric acid and tartaric acid in most supermarkets. However from my experience in making paneer, citric acid still imparts a fairly strong taste. Haven't though of trying tartaric acid for some reason. You could try various acidic fruits I guess. Pineapple or green kiwifruit perhaps? Perhaps even lime will be a taste you find okay. While looking in to tartaric acid for making paneer I found this [6] where they also tried lactic acid and ascorbic acid (you'll want to be careful you don't overdose on vitamin C I guess). Finally you may want to do a few tests, perhaps you're using way more lemon juice then you need? Nil Einne (talk)
C is water soluble and it's very hard to get an overdose. A and D and the other fat-solubles are the problems for overdose. I'll have to look at a different grocery store. Safeway (US, Washington state) doesn't carry citric and tartaric from what I've seen, though I guess I've never asked. SDY (talk) 20:46, 17 January 2011 (UTC)[reply]
The vitamin C article says it exhibits remarkably low toxicity, the LD50 for an average person would be over 800 grams, and "The mechanism of death ... may be more mechanical than chemical". :) 81.131.16.71 (talk) 20:58, 17 January 2011 (UTC)[reply]
Okay no concerns for ascorbic acid then so that's one possibility. I should clarify the citric acid and tartaric acid I'm thinking of is normally available in crystalline form, see [7].
This result from a search for 'where to buy citric acid' may be helpful [8] (the purpose there may not be food related but most of the suggestions sound like they will be fine). In particular a brewing shop may be something to look in to. I know someone who makes their own energy gels and citric acid is used, so perhaps a health food or sports/exercise supplement shop will also have something (although they may just want to sell you premade stuff). [9] (UK apparently) suggests a home brewing shop as well hence my recommendation.
P.S. Reading the forum suggestions a little more closely, it also sounds like you may not want to (try to) purchase too large quantities...
Cheese-making supply shops sell citric acid. --Sean —Preceding unsigned comment added by 208.54.44.51 (talk) 00:25, 18 January 2011 (UTC)[reply]
Flash flood tanks
Can a flash flood carry and destroy an army tank? --109.78.87.34 (talk) 21:26, 17 January 2011 (UTC)[reply]
I don't see why it couldn't carry one away. Flash floods can remove houses from their foundations, and in terms of absolute weight, a house is heavier than a tank. "Destroy" may be a harsh word, but I could see a tank being lifted off its treads and moved by such a flood. --Jayron32 21:34, 17 January 2011 (UTC)[reply]
From M4 Sherman: 66,800 pounds / (5.84 m * 2.62 m * 2.74 m) = .723 g/cm3 leading to the surprising result that tanks float. Of course that assumes that it's a cube, which it isn't. It's probably denser than that, but it's still reasonably close to the density of water, so water will have no trouble carrying it. Houses float too BTW, that's the main reason flash floods can move them. Ariel. (talk) 21:57, 17 January 2011 (UTC)[reply]
I don't believe so, or at least not to a catastrophic degree. Many modern main battle tanks are capable of deep wading, which means they can drive through water that's as deep as they are tall (with the help of a snorkel) - see File:Zwei_Leopard_2A5_beim_durchqueren_eines_Gewässer.ogg where two modern Leopard 2 MBTs ford a river, with only their snorkels and the ends of their gun barrels above water. They can only achieve this if they're heavier than the water they displace (that is, that they don't float). It seems other MBTs, including the T90 and the Abrams M1 can deep wade too. So that demonstrates that, fully immersed in water, they have enough net downforce to allow the treads to engage enough to drive the vehicle through the river at some speed (which shows they're not just on the ground, they're still quite firmly on the ground). There have been fully amphibious ("swimming", which means floating) tanks, like WW2's Swimming Sherman, but those either needed an inflatable float (see DD tank#Sherman DD) or to be specifically designed to float (like the lighter Expeditionary Fighting Vehicle). Now whether the driver of a wading tank fancies the idea of driving it around in what has become essentially a murky, obstacle-filled, fast-flowing river is another matter. The wading capability is designed either for hot landings on beaches from landing craft, or for fording rivers, so they're not designed to be terribly effective at doing anything but going in a straight line in water, and not for very long. -- Finlay McWalter ☻ Talk 22:23, 17 January 2011 (UTC)[reply]
Maybe it's the difference between loaded weight and unloaded. Probably the number given in the article is for unloaded. Also a tank is not a cube, so the simplistic volume calculation is certainly too large. I was just going for an order of magnitude calculation. Ariel. (talk) 22:54, 17 January 2011 (UTC)[reply]
There's not much difference, that I can figure, between the loaded and unloaded weight. Looking at the Leopard 2, I reckon its ammo (43 rounds at 25 kg/round) weighs 1075kg, the fuel (1160 litres of diesel at around 0.84 kg/litre) weighs 975kg, and if three of the four crew swim for it (say 3 x 100kg) that's 2.3 tonnes. That sounds like a lot (it's more than two cars) but when you consider the full Leopard 2 weighs in at a jaw-dropping 62 tonnes, the laden/unladen differential is only 4% or so. -- Finlay McWalter ☻ Talk 23:17, 17 January 2011 (UTC)[reply]
It seems that a "flash flood" can mean anything from an accumulation of rainwater at low points of streets where the water is essentially standing still, to a vertical wall of water roaring through a canyon downstream of a failed dam. A tank should have decent chances of operating in the former, but has essentially no possibility of surviving the latter.
As soon as the flooding water is flowing, lateral forces on an obstacle become at least as important as byoyancy. –Henning Makholm (talk) 22:56, 17 January 2011 (UTC)[reply]
For an extreme example, the Johnstown Flood picked up and moved entire locomotives; I am pretty sure such locomotives compare favorably in terms of density and weight to a tank. --Jayron32 00:11, 18 January 2011 (UTC)[reply]
And floods aren't just water moving, either. There's stuff being carried in that water. Boulders. --jpgordon::==( o ) 07:21, 20 January 2011 (UTC)[reply]
January 18
Rocking Cooking Pot
What causes a (metal) cooking pot (no handle) to rock from side-to-side when on a stove burner (electric in my case) just as the water is about to boil? This motion can be halted temporarily by grasping the pot briefly. When released, the rocking resumes.--Koosharem (talk) 01:20, 18 January 2011 (UTC)[reply]
Even before proper boiling, bubbles form in the water. These bubbles can exert forces on the walls of the pot. It could also be from Cavitation, which is the net effect of lots of tiny shock waves created by tiny bubbles collapsing. --Jayron32 03:03, 18 January 2011 (UTC)[reply]
Short, uncomplicated answer - The water is moving. Roger (talk) 07:43, 18 January 2011 (UTC)[reply]
undetectable viral load risk
how risky is it for those that have unprotected sex with someone that is hiv+ but has an undetectable viral load? I know that most people get HIV from other people that have just gotten it because those people have the highest amounts of replicas of the virus in their bloodstream. I know it is less likely that you would get hiv from someone on antiretrovirals or that is undetectable but is it nearly safe sex or not? Are there any statistics on this? Where would I find the answer to this question?Thisbites (talk) 01:29, 18 January 2011 (UTC)[reply]
How do I access a previously asked question.eg Jan 8 2011? —Preceding unsigned comment added by 118.208.117.68 (talk) 02:01, 18 January 2011 (UTC)[reply]
Arthur C Clarke and others have postulated "Gossamer thin sails" for interstellar travel using light presure.Since light by definition is massless how can it exert pressure to 'fill' the sails?
John Cowell118.208.117.68 (talk) 02:15, 18 January 2011 (UTC)[reply]
Photons (light) have momentum even though they have no mass. In modern physics, relativistic momentum is more complicated than just the simple "mass × velocity" relationship; in fact, momentum is related to the mass, velocity, and energy of the particle, according to a Lorentz transform. (So, even zero-mass photons can have non-zero momentum). This was formalized by Einstein as part of the theory of Special Relativity. Nimur (talk) 02:25, 18 January 2011 (UTC)[reply]
Photons have no rest mass. However, they clearly have energy and energy is mass, so anything which has energy can also exert a force. The photoelectric effect, not-so-coincidentally also described by Einstein at the same time he explained special relativity is an atomic-scale example of a massless photon moving a massed particle (the electron). It works just as well on solar sails. --Jayron32 03:00, 18 January 2011 (UTC)[reply]
Photons are not massless. They have no rest mass (or to put it another way, at rest they don't exist), but while in transit they do have mass. Ariel. (talk) 03:01, 18 January 2011 (UTC)[reply]
There's no disagreement about the physics here - this is strictly a matter of semantics and terminology. I use the term "mass" to specifically refer to rest mass - as do many physicists. An equally-valid but different definition of the unqualified term "mass" refers to the sum of the rest mass plus the normalized kinetic energy, per mass-energy equivalence. Photons have an exactly-zero rest mass. Many physicists (myself included) thus say "it has no mass." Many other physicists dislike this terminology, and always use "mass" to refer to relativistic mass. I don't think we need to devolve in to word-mungling pedantry over this, because we're all in agreement about the actual phenomena. See the mass article, the terminology section, and the list of reference texts and papers for a bunch of different opinions about which definition is "better." Nimur (talk) 04:08, 18 January 2011 (UTC)[reply]
I wasn't arguing with you (not sure if you thought I was), it was a reply to the OP. I prefer to assign the word mass to relativistic mass because that's the one you need to use for calculations - momentum, gravity, inertia, etc. The trouble with doing so is that relativistic mass is not a constant (because it depends on who you are comparing it with), so I understand the arguments for assigning it to rest mass. Ariel. (talk) 04:22, 18 January 2011 (UTC)[reply]
Energy in a magnet.
For more than 20 years I used a 3 inch magnet on a daily basis.It was so strong it would fly out of my hand if I got too close steel and the only way to release it from the deck of my truck was to slide it to the edge and carefuly remove.As a tool of trade for a scrap metal buyer it even exerted a 'pull' on 304 and 316 stainless steel.It was used for holding steel for welding,holding spring doors open etc.It would have lifted the equivalent of hundreds of tons over the years without diminishing in strength.
How can so much potential energy be incorporated in something so small,how is it stored and calculated,and surely there must be a multitude more practical uses for such a mini powerpack other than computers and maybe speakers?
John Cowell118.208.117.68 (talk) 03:07, 18 January 2011 (UTC)[reply]
The nutshell answer is that a magnet exerts force, which is neither energy nor work. Work, rather, is force acting over a distance. When the magnet leaps from your hand to the steel, it's done some work, because it's moved. However, it's then stuck to the steel and does no further work. For it to move again, you've got to do work of your own (counteracting the work the magnet did) to get it back away from the steel. As for other practical uses (I'll leave aside whether they're more practical, as computers are way up there), magnets are essential to electric motors, generators, transformers, and medical devices. — Lomn 05:14, 18 January 2011 (UTC)[reply]
I was thinking about this the other day again because magnet questions are quite common on the ref desk. Maybe someone has used this analogy before but I thought a spring analogy might be good at illustrating the difference between force and energy. A loaded spring exerts a strong force, try holding a strong spring closed just with your arms for a long time! It can take a lot of energy on YOUR part. But a spring can only do an amount of work relative to its length and force it was loaded with to begin with. Once a spring is "unloaded" that's it, no more force. Same as a magnet. Vespine (talk) 05:48, 18 January 2011 (UTC)[reply]
OP, This is by no means the first time a human has had this thought! :) Magnets are quite baffling until you understand how they work. It's the mystery of magnets that has led men on life-long fruitless and often fraudulent attempts at gaining "free" energy/money (Steorn, for example). Until a material is discovered that can block magnetic fields, no "work" can be done by them, just simple attraction. They are still fun to play with thoughZzubnik (talk) —Preceding undated comment added 12:39, 18 January 2011 (UTC).[reply]
This work has some interesting things to say regarding the science behind magnets. --Jayron32 14:43, 18 January 2011 (UTC)[reply]
For those of you wondering, the song in the link Jayron gave is the source of the "Fucking magnets, how do they work?" Internet meme (which may not really be a meme, the talk page argues...). Also, I never realized people got hung up about the use of the word "miracles" in that song :rolleyes: TomorrowTime (talk) 15:16, 18 January 2011 (UTC)[reply]
I'd like to point out the enormous work I do every day by exerting a force of mumble Newton with by behind to the seat of my chair - not to mention the nightly work quota I exert on my bed. ;-) --Stephan Schulz (talk) 17:32, 18 January 2011 (UTC)[reply]
The Tesla is not actually a unit of energy, so you can't say how much energy it takes to make a magnet of a certain strength. And yet, it would be interesting to know how much actual energy it takes to turn a non-magnetic chunk of metal or rare earth into a powerful magnet like the one described; and conversely whether there is any theoretical way by which the entropy of the magnet as it degrades from perfect order could be used to drive a thermodynamic process that produces work. Hmmm - is this the same as a measurement of any excess thermal energy released if the magnet is pulverized under a powerful ram? I would think that the amount of energy needed to create two magnets of opposite polarity must exceed the amount of energy they release by coming forcefully together - I suspect that this is by some large factor - I wonder what physical factor describes this necessary limitation on the ease with which permanent magnetism can be induced in a material. Wnt (talk) 06:10, 19 January 2011 (UTC)[reply]
I suspect that the 'crushing' process would actually be endothermic, not exothermic. Ordered, aligned spins in a ferromagnetic material have a lower energy than randomly oriented spins; you have to put in energy to break the alignment. At the Curie temperature, a phase transition occurs when you move from aligned to random spins; this shows up as a measurable endothermic bump by differential thermal analysis. Similarly, if you just pull aligned-spin particles or domains apart without jumbling their orientations, that costs you energy as well — the energy of aligned spins is lower than the energy of the free or separated particles. TenOfAllTrades(talk) 14:30, 19 January 2011 (UTC)[reply]
Well, I have to admit, you're right about that. My intuitive feeling was that a pile of powdered magnet shouldn't spontaneously assemble into a powerful magnet ball - I wonder if that was also false. Wnt (talk) 18:07, 19 January 2011 (UTC)[reply]
Will an object past the event horizon of a black hole inevitably reach the singularity?
An object around a gravitational body like the Earth can orbit indefinitely if its velocity is sufficiently high, but is it possible for an object to remain stationary within a black hole? Likewise, can an observer past the event horizon perceive other objects? By definition, light can not escape the horizon, so would it be impossible for photons to reach the observer from further within the black hole? —Preceding unsigned comment added by 68.40.57.1 (talk) 03:27, 18 January 2011 (UTC)[reply]
Yes, in case of Schwarzschild black hole, object that crosses event horizon reaches the singularity sooner or later. All the paths inside of event horizon lead to singularity. So harder it tries to avoid, sooner it reaches singularity. For other types of black holes (charged or rotating black holes), there is possibility of avoiding singularity. I am doubtful whether an object can remain stationary within a black hole. About your last question, are you asking whether photons from within black hole can reach observer who is outside event horizon? No, photons cannot escape from black hole. Or, are you asking whether observer within the black hole can observe photons? Yes, observer falling inside black hole continues to observer things according to his clock, he cannot determine whether he has reached event horizon or has crossed it. - manya (talk) 04:21, 18 January 2011 (UTC)[reply]
To clarify, I was asking whether the observer within the event horizon can detect photons from further inside the black hole. Also, your statement regarding the observer not being able to determine whether he has reached the event horizon is in contradiction of the article on it. --68.40.57.1 (talk) 04:34, 18 January 2011 (UTC)[reply]
No, it is exactlyt confirmed by the event horizon article. Let me quote it for you. "An observer crossing a black hole event horizon can calculate the moment they've crossed it, but will not actually see or feel anything special happen at that moment." --Jayron32 04:40, 18 January 2011 (UTC)[reply]
I presume you meant to say "within the event horizon", not "within the singularity". Yes, for a while an observer inside the event horizon will be able to see an object that's further inside the black hole, that fell in shortly before the observer. However, the object will rapidly move further away from the observer, due to the extreme tidal forces, and the object's image will become red shifted, to the point where the observer soon won't be able to see it at all. In other words, the appearance of the object will qualitatively appear very similar to the appearance of an infalling object as seen from an observer that's outside the event horizon. Red Act (talk) 06:16, 18 January 2011 (UTC)[reply]
You have to be specific about what you mean by "further inside", because black hole spacetimes are nothing like the ordinary flat space where concepts like "inside" are normally defined and make sense. The most obvious thing you might mean by "further inside" is that the Schwarzschild r coordinate is smaller. Outside the event horizon, that coordinate measures distance from the center of the hole, more or less. Inside the event horizon, though, it measures time. The singularity is in the future, not in a particular place, and "further inside", in this sense, would really be "later in time". You can't see the future, even inside a black hole. You can, however, see objects that crossed the event horizon before you did. The easiest way to understand how this works is to look at a diagram like the one to the right. Ignore everything but the upper right quadrant. The straight diagonal line is the event horizon; below and to the right of that is the outside world; above and to the left is the black hole interior. The singularity is the boundary of the grey region. The grey region itself is nothing (it's not part of the solution). The past is down, the future is up. Light travels along 45° diagonal lines. You can only cross the event horizon from right to left, since you're limited by the speed of light. If you draw two sub-light worldlines crossing the horizon, it's easy to see that light from the first one will reach the second, so you can see someone who crossed the horizon before you did. You will hit the singularity before you see them hit the singularity, though. The animated blue lines are lines of constant Schwarzschild r. -- BenRG (talk) 07:25, 18 January 2011 (UTC)[reply]
Ticklish sensation near forehead
If an object is brought close to my forehead, but does not touch it, my forehead becomes sensitive and starts tingling and becoming very "ticklish", for lack of a better term. For several years, I've asked certain people if they've had the same sensation, and I've only met one girl who did. I have unsuccessfully tried testing the sensation with my eyes closed. As the object (any object) is brought closer to the forehead, the sensation deepens. It used to be really bad when I was a child, but now as an adult, I hardly even think about it anymore. It just popped into my head a minute ago and I decided to ask about it :)Reflectionsinglass (talk) 03:56, 18 January 2011 (UTC)[reply]
You are not alone.[10] -- I'm particularly interested in this comment from DocCathode:
"Nothing supernatural about it. It's a mixture of a sense of danger/discomfort, the urge to move away, and the repression of that urge.
"To prove this, you need a friend who trusts you and follows instructions. Tell them to stay still, and to open and close their eyes when you tell them. Begin approaching with finger about two feet away. Tell them to close their eyes. Move the finger foot closer and tell them to open their eyes. Tell them to close their eyes. Move the finger to six inches away. Tell them to open their eyes. Tell them to close their eyes. Move the finger to three inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to two inches. Tell them to open their eyes. Tell them to close their eyes. Move the finger to an inch. Tell them to open their eyes. Tell them to close their eyes. Move the the finger to half an inch from their forhead. Tell them to open their eyes. Tell them to close their eyes. Slowly and quietly move your arm away from them. Tell them to open their eyes.
"The tingling sensation is most intense the last time, despite the fact the no object is near their forehead."
Please try that and let us know what happens. 71.198.176.22 (talk) 05:57, 18 January 2011 (UTC)[reply]
what killed Dinosaurs
I read an article that had say something about the death of mamots in 35000years ago that may be general for last happening for dinosoros 0 the radiation of any supper nova can kill dinosoros
in some million years ago. A.mohammadzade jan 18 iran —Preceding unsigned comment added by 78.38.28.3 (talk) 04:23, 18 January 2011 (UTC)[reply]
I'm not sure I understand your question properly. Dinosaurs became extinct during the Cretaceous–Tertiary extinction event. There are various theories about what caused this to happen. The most popular theories have to do with an asteroid (or asteroids) hitting the earth. You may also find the simple wikipedia article or the farsi wikipedia article on this topic to be helpful. Calliopejen1 (talk) 04:55, 18 January 2011 (UTC)[reply]
3500 years ago? Are you thinking about Noah's flood (Nuh in Islam)? According to the (Christian) Ussher chronology this occurred 2348 BCE. Modern science places the dinosaurs extinction to the Cretaceous–Tertiary event 65.5 million years ago (as Calliopejen1 noted), and woolly mammoths to about 10 thousand years ago. BTW, several web-browsers have spell-checkers for their text-entry boxes; you should consider installing one for all the languages you speak. CS Miller (talk) 05:36, 18 January 2011 (UTC)[reply]
Actually, the OP said 35,000 years ago, not 3,500 - no need to drag young earth creationism into this. As you note, mammoths were still alive and well at that point, so it's a curious date to bring up. Our article on 35,000 BC No, we don't really have an article on that date, but it is a nice redirect... doesn't mention anything particularly germane. 15:08, 18 January 2011 (UTC)
Ooops. My apologies. I can only think the lack of punctuation made me not see one of the zeros, and conflate the OP's timescale with that of YECs. CS Miller (talk) 17:05, 18 January 2011 (UTC)[reply]
There is really no question that the asteroid killed the dinos. Headline writers and popular science in general will never tire of stirring up controversies, but a panel of 41 international experts have met and agreed that there is consensus on the cause. This is mentioned in the articles. Imagine Reason (talk) 00:00, 19 January 2011 (UTC)[reply]
Actually, I killed the dinosaurs. It was a time travel mistake, sorry, but when you gotta sneeze, you gotta sneeze. I take no responsibility for the mammoths, though. I think Baseball Bugs did them in. --Ludwigs2 00:04, 19 January 2011 (UTC)[reply]
I thought Tezuka killed the dinosaurs. — DanielLC 06:02, 19 January 2011 (UTC)[reply]
What is the fastest growing, soil erosion preventing, preferably edible plant suitable for San Francisco's climate? 71.198.176.22 (talk) 05:47, 18 January 2011 (UTC)[reply]
Lespedeza are commonly used in the Southeastern U.S. and meet all of your requirements except edibility. Not sure if it will grow in the Bay area, however. --Jayron32 05:53, 18 January 2011 (UTC)[reply]
never say death star for pulsars
the crab nebula is sending several rays and is alive there in space . the heart of the star is sending palses so we ought never say the super nova has died . a. mohammad zade iran --78.38.28.3 (talk) 06:06, 18 January 2011 (UTC)[reply]
There is no question that the crab nebula article uses the term "dead" only when citing [11]. 71.198.176.22 (talk) 06:03, 18 January 2011 (UTC)[reply]
when the earth was shining
i think that the earth was shining for some million years . if you want to know why then that will explain with my new theory a. mohammad zade
Why don't you ask whether your theory is consistent with the evidence so we can critique it for you? To do so, you would have to explain it. It is true that the elements heavier than iron came from supernovae in the Earth's distant past. 71.198.176.22 (talk) 06:06, 18 January 2011 (UTC)[reply]
thanks for giving commnets .i will soon write my theory hear i have some problems in safe evaluation andpublishing . so i save it such as patent . it will wrote here as soon as i published .--78.38.28.3 (talk) 06:13, 18 January 2011 (UTC)[reply]
Wikipedia is not the right place for people to develop their new theories. See our WP:Original Research policy. Comet Tuttle (talk) 18:38, 18 January 2011 (UTC)[reply]
Pre-existing conditions and Medical Insurance
I really don't understand why people who have a pre-existing conditions are making SUCH a big deal out of having to pay more for insurance. I understand they get mad if they are denied, but they should have to pay more. It's the same way I have to pay more for auto insurance because I am younger and have had several speeding tickets in the past few years, I am a greater risk. Many (not all, but many) CHOOSE to have these pre-existing conditions. Many people who are obese, choose to have several other related problems, many people who high cholesterol choose to have it, same with so many other conditions. Is there a flaw in my thinking? I'm already paying over $200 a month for insurance when I don't ever use it because of all these abusers, when I am perfectly healthy, take care of myself, follow a healthy diet, and go to the gym 5 days a week. If everyone was covered, it would just make the problem worse and more expensive for everyone. —Preceding unsigned comment added by 76.169.33.234 (talk) 07:44, 18 January 2011 (UTC)[reply]
What country are you from? People there might be grateful they don't live here in Australia. Here, if you have a pre-existing condition, you can be denied any benefits for treatment of that condition for 12 months after taking out the insurance; but after that, you're fully covered like everybody else. There's no alteration to premiums, though; that's strictly outlawed. -- Jack of Oz[your turn] 08:00, 18 January 2011 (UTC)[reply]
USA. I don't know how people think in Australia or in other countries, but I work in a pharmacy and my customers think just because they are taking a cholesterol medication, they can eat whatever they want. My customer was joking about it the other day. —Preceding unsigned comment added by 76.169.33.234 (talk) 08:04, 18 January 2011 (UTC)[reply]
Yes, insurance companies have to discriminate, but it's sometimes hard to be tough on those with self-inflicted conditions while being fair to those whose ailments are innocently gained. HiLo48 (talk) 08:09, 18 January 2011 (UTC)[reply]
No, insurance companies don't have to discriminate, but only if you run a system of compulsary insurance. This is what happens, in one form or another, across most of the developed world: compulsary insurance with a ban on discrimination. Physchim62(talk) 12:39, 18 January 2011 (UTC)[reply]
I'm actually kind of struck by your first sentence. My fiancee, in trying to get private coverage, has been rejected by every insurer in California due to a pre-existing condition, which we're told will continue to be the case for another couple years. This is not a matter of paying more - she's not even allowed in the existing high-risk pools. I hate to think where she'd be if neither she nor I had a job. HIPAA and COBRA (expensive) do ignore pre-existing conditions, but they are not available to everyone. As for whether people choose to have a pre-existing condition, I have no comment. Someguy1221 (talk) 08:15, 18 January 2011 (UTC)[reply]
HIPAA is a health information privacy act, not an insurance company. COBRA is Federally mandated insurance coverage for those who recently left employment. I do not see how those apply in the context you are using. -- kainaw™ 17:28, 18 January 2011 (UTC)[reply]
Further, California has a state managed program specifically for high-risk patients who have been denied insurance. It is explained here. -- kainaw™ 17:31, 18 January 2011 (UTC)[reply]
I wasn't even aware of that plan, thanks (but thankfully she has a job, and I don't even want to know how much that costs). I was referring to HIPAA health plans, by the way. I was using both that and COBRA as examples of coverage potentially available to individuals with pre-existing conditions who do not get such coverage through their current employer, or who are unemployed. Someguy1221 (talk) 00:04, 19 January 2011 (UTC)[reply]
Really it is a question of what costs we think are fair to spread across society, and which we don't. If you happen to be develop a terribly expensive health condition, through no fault of your own, should society bear this cost, or should you? Thinking from a position behind the veil of ignorance, one might prefer to spread such costs across society. Also, you note that some health conditions are in part caused by deliberate choices. This may be true, but most health conditions are not, and what sort of surveillance regime would be necessary to monitor which people this applies to? Such surveillance would likely be prohibitively expensive, as well as intrusive on privacy. Thinking forward into the future, as genetic health data becomes more readily available, it is plausible that insurance companies could very easily calculate your health risks to a much greater precision. (Assuming this were legal.) Is this something you would want? It is essentially just an extension of your principle of paying a premium that reflects your health risks. It would assign costs much more precisely to the individual, but it would change the nature of health insurance as we know it. Now, health insurance effectively insures against the risk that you will get Alzheimer's, for example. In the future, perhaps it would already be known that you will get Alzheimer's (even now, there are some genetic markers identified that are highly correlated with it). Then, since your premiums would already reflect your future disease, you would bear the cost for your Alzheimer's treatment, and your insurance would only be effective against risks such as being hit by a car and needing emergency surgery. Would this be preferable? To me, probably not. YMMV. Calliopejen1 (talk) 11:11, 18 January 2011 (UTC)[reply]
What does this have to do with science? thx1138 (talk) 13:01, 18 January 2011 (UTC)[reply]
Generally this is misplaced, although the degree to which disease is a "choice" could be more scientific. After all, obesity and even high cholesterol are controlled by genetic and other propensities (I suspect that there should be a dramatic role for epigenetics here...) I feel that nothing but prejudice controls what people like the OP pick out as a "choice" - after all, the commuter who suffers injuries in a traffic accident also made a choice, right? The skier who leaves his testes with a buried pole on the slopes, likewise. The HIV victim, few would disagree, but what about the victim of flu or rotavirus or meningitis or malaria, who could have avoided it all just by staying inside his front door?
It may be more for the humanities desk to answer what the point is of having insurance if suffering a diagnosis means being denied insurance. Why not just keep your money and pay as you go, with no private bureaucrats pretending to serve you by driving up costs? The problem is, no one wants to be diagnosed with anything, and as they are servants only of corporations and government the doctors are trusted far less than Mafia bookies, so preventative care becomes a pretty myth. Wnt (talk) 15:30, 18 January 2011 (UTC)[reply]
"Why should society pay for the consequences of someone's bad choices?" begs the question of bad things happening to people who have in no way brought it on themselves. It is a reasonable question whether a society should spread the medical costs across all members, or have a "Every man for himself and the devil take the hindmost" lifeboat ethic. A person can be bopping along, healthy as a horse at 20 and at 30, and at 40, never took a sick day, eating right, not smoking, exercising regularly, then suddenly they have some crippling injury or ailment, like a debilitating and persistent and ineradicable infection, or a crippling injury, or cancer, or heart disease, or insulin dependent diabetes, with little hope of getting individual health insurance from a for-profit insurer. Many Americans live in a fantasy world where they will always have a policy from work. If the hospitalization means you can't work, and you don't have or lose your employer-provided insurance, you are just out of luck when you need surgery or hospitalization which might cost $100,000. Figure on losing the home and spending every dollar of retirement savings. "Move in with the folks" is not an option when they are dead and gone. Even if someone with severely impaired health found a private insurer, it would cost more per month than they could pay, especially if they are not healthy and can only work part time or a lesser pay level than their previous fine career allowed. "Paying more for insurance because of a preexisting condition" may mean paying an extra $12,000 a year more than the basic insurance, or even more than that, which the unwell person simply cannot afford. According to a report, "80 percent of people with diabetes were uninsured after they lost health insurance coverage due to loss of a job or job change, divorce, change in income or health status, or a move. " It is not presently affordable for them. Over 50 million Americans have no health insurance, so that if they do go to see a doctor or have tests, they must pay "list price," typically several times what the cost is for those with insurance, since Blue Cross et al reduce the price to a fraction of what the doctor, hospital or lab says it should cost. For instance, Xrays that the insurer writes down to $100, and which cost me $15 out of pocket, would have cost the uninsured $350. An EKG that would have cost the uninsured $1100 got written down by the insurer to under $300 (and only cost me under $30). Edison (talk) 16:59, 18 January 2011 (UTC)[reply]
Fom a european persepective the "devil take the hindermost" American health care system, or lack of it, is scandalous. Add that to guns being used freely, with gun-murders being 100 times more common per capita. They are not good adverts for the US. 92.24.183.183 (talk) 14:42, 19 January 2011 (UTC)[reply]
While I agree with all that you said (in particular, many medical conditions are not or not fully the result of irresponsible choices), there is also another aspect: It might be cheaper to pay for the effect of someones bad choices. Sick people typically can contribute less to society - imagine Stephen Hawking without universal health care. Similarly, desperate people will do desperate deeds. Would you rather pay for someones cancer treatment via a social insurance system, or pay for more police to keep desperate husbands, wives, or parents from robbing banks to pay for treatment? --Stephan Schulz (talk) 17:24, 18 January 2011 (UTC)[reply]
This is a valid point, but it really doesn't go far enough. Society has prevented disaster by various back-door ways of paying for health care for the poor, such as hospitals providing care and then just not getting paid for it, then working the costs into care for other patients. But hospitals have become more and more commercialized, with less profitable sites even shutting down, and if political efforts to correct the situation are rebuffed, then you're left with a situation where a segment of the population denied access to health care would begin to turn on it as an enemy. The effect of even a single ambulance bomb would be devastating (and how do you apply security precautions?). The effect of three or four simultaneous attacks against all remaining hospitals of a metropolitan area would essentially put major health care out of commission for a hundred miles in any direction - even if such a homegrown al Qaida didn't manage to get their hands on the radiation sources inside the hospital ... Wnt (talk) 05:12, 19 January 2011 (UTC)[reply]
I have a concise answer: The argument (that people with pre-existing conditions should just suck it up and pay a lot more for their medical insurance) makes complete sense from an actuarial point of view, but it collides with many people's belief that a society should take care of its sick, even though this makes insurance more costly for the more-healthy. Comet Tuttle (talk) 18:37, 18 January 2011 (UTC)[reply]
Yes. Once we have decided we will not let people simply die on the street, then we must assess the cost of emergency treatment and conclude that an ounce (or penny) of prevention is worth a pound (dollar) of cure, therefore the next step is to try to fund preventative care. Because whether through taxes or insurance premiums, you still have to pay for the sick, so might as well pay less for better results. SamuelRiv (talk) 22:10, 18 January 2011 (UTC)[reply]
This isn't really a science issue and is OT on the RD anyway but that probably applies to most of this discussion. The above is one of the arguments for measures to tackle obesity, smoking and other problems as well as encouraging healthy eating, exercise etc in countries with some sort of socialised medical care. Of course depending on the measures this can lead to claims of nanny state, food police, sin tax and whatever else and measuring the efficacy of such measures is generally difficult at best. And I've seen it argued smokers at least actually cost the system less in the long run, particularly where there are other costs (e.g. in NZ where a government funded pension is something most citizens past a certain age are entitled) due to the shorter lifespan even with their added medical bills. (Of course you then get in to complicated issues like whether they contribute less.) Unrelated to this but related to the earlier point you also get the complex issue of how much should be spent on treating people with a given expected outcome. For example, is it worth spending $100k on treatment that may increase the chance of living past 5 years from 5% to 10%? (Very simplistic of course, the outcome of many treatments come in things like improved quality of life which are generally subjective.) Ironically this was seen to some extent in the US with the recent debates when the death camps nonsense came up. Nil Einne (talk) 22:46, 18 January 2011 (UTC)[reply]
Most of the others have hit the main points here, but I just want to point out that insurance that covers you when you are healthy, but not when you are sick, is not really insurance. That's just a series of subsidized physical exams. The entire point of insurance is that you pool the resources of many so that when others are in hard times, they have resources as well. It is a sign of how screwed up the American medical system has become that the basic notion of insurance has been completely forgotten by most Americans, who just understand it as "the way I pay for routine checkups and prescriptions." It's about spreading the risk, plain and simple. --Mr.98 (talk) 03:30, 19 January 2011 (UTC)[reply]
The deal with paying for routine checkups is that's how the insurance companies manage their own risk. The costs of dealing with tragic diseases goes up considerably the later they are treated; insurance companies actually save themselves money by making sure you go to the doctor regularly to for physicals, and to get even "nuisance" issues checked (like the non-specific and usually benign but occasionally deadly "Flu-like symptoms"). The ideal "deal" between insurance companies and their customers is something like "You agree to get checked by doctors more often, and we'll cover it when shit goes really bad". Same deal with prescription coverage; people would forgo necessary medicine if it's too expensive, and on the bulk these people will end up costing the insurance companies much more if you end up in the hospital getting treated for something your medicine could have prevented. This is not a defense of the American insurance industry at all; they've basically dropped the ball with regards to their fiduciary responsibility towards their clients. But in theory, the system is supposed to work as I describe. --Jayron32 05:26, 19 January 2011 (UTC)[reply]
Isn't it the insurance company's fiduciary duty to do the bare minimum to brand the sick person with a permanent record of poor health, and help their client (the employer) to get rid of the problem before it amounts to a major expense? Wnt (talk) 18:11, 19 January 2011 (UTC)[reply]
Thank god for the National Health Service. It has made me disinclined to emigrate to a sunnier cheaper or less crowded country as I would not have the piece of mind of knowing that I would get unlimited free health care if I needed it. See also Publicly funded health care. 92.24.183.183 (talk) 13:17, 19 January 2011 (UTC)[reply]
I am the OP, sorry it took me so long to get back to this post....
Edison, you are really sucked into the idea that obesity and high cholesterol is almost all about genetics, when it has little to do with it. The issue here is that for a genetic defect (not sure if this would be the right word) to be present, it would require the proper environment. Almost every single obese person eats horribly and that is a choice. Same with many people with high cholesterol. You can be thin and have high cholesterol, but if you really take a look at it, almost every single person with high cholesterol is overweight, many of them even obese. If you look at both groups, neither one in almost every consumes a "healthy" or a low calorie diet (low cholesterol diet in the high cholesterol patient) and they almost never exercise if they do at all. Most these people "think" they know how to diet, but they have no clue, they think 3000 calories a day or more is a diet. They think exercising is walking around the block or taking the stairs instead of taking the elevator. Try going into the gym and pounding the weights for an hour and then doing 45 minutes of hardcore cardio 5 days a week and then lets see if you still have high cholesterol or are obese after a year doing that and consuming a low calorie diet. I can guarantee you over 90% of the people will be cured as long as they keep it up.
Now lets discuss choices in life. Everything you do is a "choice." Many or all of them involve some degree of risk. Everyone knows that driving a car involves risk, you can get into an accident. Some people choose to take that risk and some paranoid people or people that have been in very bad accidents that have not recovered emotionally choose to not take that risk. So is it a choice? Yes, it is. At my age, I choose to take the risk of maxing my car out to see how fast it goes on the freeway. I know there is more risk involved going very fast, but if I had children, I would not take that risk. Same with skiing, there is a risk involved. An example that may be more clear would be weight lifting, there is a great deal of risk involved. Personally, I choose not to do some exercises at the gym because of the risk involved. And yes, even with sex and contracting HIV there is a risk. Have you not heard of getting tested yourself and having your partner tested before you have unprotected sex? Do you think its a good idea to have sex with a woman or a male that has had 50 partners in the past? Would you take that risk? Some people would, some people wouldn't. That is called a choice. There is a distinction between acceptable risk and unacceptable risk.
The real issue here is that many diseases are preventable. Look at most people with type 2 diabetes. If they lose the damn weight and exercise, most of them would be cured. I work with one of them, he has either Jack in the Box, Kentucky fried chicken, or McDonalds every single day. Then he has 2 snickers and peanut M&Ms on top of it. He has high cholesterol and is overweight because of all that junk too. He never goes to the gym and has no interest at all in dieting. His blood sugar was dangerously high before he found out (at work by the way). As previously mentioned, going to the doctor for preventative care can reduce the chances of contracting several diseases or at least you can cut down costs to treat the disease if you catch it early. Most people don't even do that and it costs us healthy people tons of money. Some older women don't get mammograms as often as they should, others don't get them at all. Some older people don't get colonoscopies. Other people don't get their yearly physicals and dont people don't want to pay for their medication and think they know better than their doctor. In the end, it costs us money. It just hurts my wallet and others when I take good care of myself, eat healthy, exercise, and get regular checkups and do everything necessary to stay healthy and other people don't and I have to pay for it. There is no reason why I should have to. ALSO, let me add something to what I originally said. I don't have an issue with supporting people who are disabled and cannot work, I don't have a problem paying for their healthcare. I'm also kind of OK supporting some people who's income is around the poverty level, but then again, I do believe if they really wanted to, they could somehow, someway, come up with the money. I mean just imagine, the last time you really wanted something you could not really afford, didn't you figure out a way to come up with the money? I always do and so do many other people. —Preceding unsigned comment added by 76.169.33.234 (talk) 09:34, 20 January 2011 (UTC)[reply]
I'm gonna skip all the non-sense rant about having to burden the expenses of other people's choices (Welcome to life in society. Go be an hermit if you don't like it) and go directly to the only point of your post worth commenting on. YOU SHOULDN'T SPEED IN THE FREEWAY JUST FOR THE FUN OF IT. I sincerely hope that you get caught next time you do it, making the freeways safer for the rest of us. Dauto (talk) 16:27, 20 January 2011 (UTC)[reply]
You have two formulas under the section "Timescale"
Two different science textbooks are quoted for the source of these formula:
B. Gladman et al. (1996). "Synchronous Locking of Tidally Evolving Satellites". Icarus 122: 166. doi:10.1006/icar.1996.0117. (See pages 169-170 of this article.
Formula (9) is quoted here, which comes from S.J. Peale, Rotation histories of the natural satellites, in J.A. Burns, ed (1977). Planetary Satellites. Tucson: University of Arizona Press. pp. 87–112.)
Do both formulas come from the same publication?PaulNethercott (talk) 09:25, 18 January 2011 (UTC)[reply]
I fixed the link for you, and placed a link on the doi from the reference. Hopefully someone has access to read the article and can check for you. Ariel. (talk) 10:49, 18 January 2011 (UTC)[reply]
The article is available online here (PDF). It gives the first formula and cites to Peale. I didn't look thoroughly for the second formula - maybe someone else can do that? (Note that the Wikipedia article does not cite the second formula to this journal article specifically, though perhaps it also comes from here.) Peale does not seem to be available online anywhere. (I searched in google books using a variety of ISBNs that seem to be associated with the book, and I didn't get any results.) If you are interested in verifying the formula in the original source, the Burns book seems to be available in many university libraries and large cities' public libraries,[12] or you can buy it through Barnes & Noble for $1.99.[13]Calliopejen1 (talk) 10:54, 18 January 2011 (UTC)[reply]
An object hanging on a string
On this page: http://www.croomphysics.com/notes/app_hewitt/chapter2.pdf (page 11) I found an answer to a question that confuses me: "Consider what would happen if you suspended a 10-N object midway along a very tight, horizontally stretched guitar string. Is it possible for the string to remain horizontal without a slight sag at the point of suspension?"
Answer: "No way! If the 10-N load is to hang in equilibrium, there must be a supporting 10-N upward resultant. The tension in each half of the guitar string must form a parallelogram with a vertically upward 10-N resultant."
I understand this for a guitar string and a 10-N load, but what if the string is replaced by a strong rope, and the load is only 1 N. Surely it must be possible to pull at both ends of the rope with enough force to make it remain horizontal without a sag??? Actually, I tried this myself with a piece of rope that I pulled apart and a pair of scissors, and there was no perceptible sag. My reasoning is that a stretched rope must be able to exert an upward directed normal force in the same way as a table exerts an upward directed normal force. Am I correct?? Lova Falktalk 13:05, 18 January 2011 (UTC)[reply]
No. Your rope cannot exert a force at right-angles to itself. The only way it can hold something up is if it is pulling up at the point of the suspended object (to cancel the object's gravitational downward pull). If it's pulling up, it must have a vertical component to its direction, which means it's distorted down from perfectly horizontal. Once you recognize "one mass, one string", there's no basis for making a cutoff "only if the mass is less than a certain amount" or "only if the string has certain elasticity". For a very light mass on a very stiff string, the deflection is just very small (because the mass is light, doesn't require much upward pull, and that can be accomplished without much deflection because the string is so non-stretchy). DMacks (talk) 13:13, 18 January 2011 (UTC)[reply]
(edit conflict) No, there should always be a sag, but the sag may not be perceptible under certain parameters. A non-ridged string should always sag in the middle if supported only at the ends, regardless of how hard you pull it. What your eye defines for you as "horizontal" may have a higher tolerance than a true horizontal. In fact, horizontal is one of the least stable positions for such an arrangement, if you look at something like bridges; all rope bridges sag in the middle; if you try to make them not sag, then you end up putting so much force on the ropes as to make them too close to the breaking point for safety. In Suspension bridges, you often engineer the roadway to sort-of "reverse sag", that is many such bridges actually have a hill in the middle, in effect redirecting the stress into the ground anchors on either side of the bridge. --Jayron32 13:16, 18 January 2011 (UTC)[reply]
Indeed, the rope will sag under its own weight, even if you don't have any additional suspended mass. If the rope's mass is uniformly distributed along its length, it will form what is known as a catenary curve. TenOfAllTrades(talk) 15:12, 18 January 2011 (UTC)[reply]
Another perspective: in physics problems, 'rope' is often modeled as a mass-less object that has tensile strength but no compressive strength. Real ropes DO have compressive strength, especially large diameter ropes of short length. A short length of thick rope (~6" diam X 3' long), anchored at both ends can support an upright load-bearing catenary like the gateway arch. This would not usually be considered 'sagging'. SemanticMantis (talk) 17:37, 18 January 2011 (UTC)[reply]
I seem to recall an unintentional verse in a book by a distinguished scientist:
as you can see here. Of course, he's talking about the weight of the cord itself, but the sentences just before that are about the case of a weight hanging from a cord whose own weight is negligible. According to Martin Gardner in a Mathematical Games column reprinted in Martin Gardner's Sixth Book of Mathematical Games from Scientific American, Whewell was annoyed to learn about the "poem" and had the wording changed in the next edition. Gardner misquotes the "poem" slightly, though. --Anonymous, 05:10 UTC, January 20/11.
Even the ground will sag if enough weight is put on it. Compressive strength means only that the material resists sagging, not that it avoids it entirely. Wnt (talk) 18:42, 19 January 2011 (UTC)[reply]
Sure, I just wanted to point out the limitations of the way string is often modeled for simple problems. In particular, a string modeled with no compressive strength cannot take the shape of an upright catenary, but a real rope can. This may help explain some of the confusion between real-world problems and physics 101 type stuff. SemanticMantis (talk) 20:59, 19 January 2011 (UTC)[reply]
What if both ends of the string are attached to spherical cows? --Jayron32 00:57, 20 January 2011 (UTC)[reply]
This basically translates into "the absolute smallest a thing can be and still physically exist", right? HalfShadow 18:23, 18 January 2011 (UTC)[reply]
Not really. It's a really, really small distance, so there are some theories that it's the fundamental granularity of the universe, but none of the well-accepted, well-proven physics theories hold that there is anything special about that length. It's just the length unit you get if you attempt to scale units such that major physical constants come out to unity ("natural units"). Keep in mind that the mass unit you get when you do that (the Planck mass, is 2.2 x 10-9 kg, about the size of a human egg cell (see Orders of magnitude (mass). -- 140.142.20.229 (talk) 18:46, 18 January 2011 (UTC)[reply]
As it says in Planck length: "In some theories or forms of quantum gravity, it is the length scale at which the structure of spacetime becomes dominated by quantum effects, giving it a discrete or foamy structure, but other theories of quantum gravity predict no such effects." Basically, we don't know what happens at such small scales. --Tango (talk) 21:56, 18 January 2011 (UTC)[reply]
I think you might fairly say that it's the absolute smallest a black hole that can exist. Any smaller, and the Compton wavelength gets bigger; but the Schwartzschild radius gets smaller. Which means that the hole is too fuzzy to fit in the hole, so to speak. So if you have a black hole that is evaporating by Hawking radiation, something ought to give out at least mathematically around this time; the Heisenberg principle says you're not supposed to know where the black hole is that precisely, but how is it going to get away? You can play a merry chase through Planck mass, Planck length, Planck momentum, Matter wave to figure this out, but one word of caution - I initially looked up de Broglie wavelength to see how the math worked out and had a curious disagreement by a factor of 2 pi (on the Planck momentum; with the de Broglie wavelength you can't say a mass has a given wavelength without giving it some arbitrary velocity). It turns out that there's a distinction between the "reduced" and "non-reduced" Compton wavelength as explained in that article. A distinction which I don't understand... you'll need a real physicist for that... :( Wnt (talk) 05:02, 19 January 2011 (UTC)[reply]
Coal mining efficiency
I saw on a TV show this gigantic drilling machine many hundreds of feet below the surface around Pittsburgh, PA and started thinking about the massive amount of energy that must be needed to turn the thing's huge and undoubtedly heavy drill bits against the resistance of the earth it was drilling through, and the energy needed to move the thing forward, along with all the energy used for the other trolley cars, lights, ventilation systems, and of course the energy expenditures to raise the mined material back to the surface, and I wonder roughly how much energy quantified as an amount of coal (I know the machines don't take coal for fuel, but I want to know the figure in terms of coal) the average coal mining plant expends in all the actions it takes to extract 100 tons of coal? Just a very ballpark estimate is all I'm after here. For instance, do they use about a ton of coal's worth of energy to get 100 tons? Do they use over 50 tons' worth? Thanks. 20.137.18.50 (talk) 18:38, 18 January 2011 (UTC)[reply]
This is a very important and valuable analytic tool: it is formally known as EROEI (energy returned on energy invested). It is heavily studied by economists, business analysts, and geoscientists and engineers in the mining and production industries. I know quite a bit about the ballpark numbers for the oil industry, but unfortunately not for coal; I imagine coal mining experts know similar metrics for coal mining. I have heard reputable petrophysicists claim that the EROI for tar sands is dramatically and dangerously approaching 1.0 in the long run; this means that it is economically unsustainable (in other words, you must use one full barrel of oil to power the extraction of one barrel of oil). Coal mining is different from petroleum, because the energy to extract coal comes from many sources: electricity (... from coal); chemical energy (from explosives... and you could trace the energy budget farther back to the factory, to electricity, and again, ...to coal); and petroleum (...imported from the oil industry). The oil industry, on the other hand, powers almost all of its field operational energy budget using energy derived from oil - so the budget is easier to balance. (Machines, drills, motors, trucks, and so on, are all diesel or even fuel-oil powered). As discussed in the article I just linked, the EROI is very difficult to measure exactly. Nonetheless, the EROIE definitely does impact the business model of large-scale energy extraction. Here is an OilDrum node on the EROI of coal. Let me know if you need help deciphering the energy-budget numbers in there. ("Lower-" and "Higher-" heating values, and so on, are all "engineering adjustments" that cloud the nice, pure theoretical thermodynamic analysis of "how many pounds of coal did we burn?") And, as one post anecdotally claims, if you still live in an area where coal can be mined with a pick and shovel, (like Indonesia), you burn zero pounds of coal to extract 1 pound of coal - a net EROI of "infinity." I would posit, based on comparative prices between coal and oil in BBOE, that coal extraction is significantly more energy-efficient than oil - let's say, 1 ton of coal burned to extract 10 tons of coal (in a developed, mechanized, American Wyoming strip mine). In the spirit of providing solid, numerical references, there's no substitute for the cold, hard economic and production statistics collected by the United States Department of Energy, and made available at no charge to the public through the Energy Information Administration website. Nimur (talk) 20:57, 18 January 2011 (UTC)[reply]
Stability
Did first-rateships of the line such as the HMS Victory have any stability problems? It looks very top-heavy. Did it go a long way under the water? And does anyone have a picture of a model of it out of water? --T H F S W (T·C·E) 18:46, 18 January 2011 (UTC)[reply]
Some of your questions are obliquely answered in the article Ship of the line. In the earliest era of European warship building when trial-and-error and guesstimation ruled, stability was indeed a problem, as witnessed by the fates of HMS Mary Rose (1509) and Sweden's Vasa, but by Victory's era Naval architects worked by well-established scientific laws. Some of the more basic means of achieving stability are ballast below the waterline and the 'tumblehome' or inward angling of the upper decks, which significantly improved weight distribution. 87.81.230.195 (talk) 19:25, 18 January 2011 (UTC)[reply]
And does anyone have a picture of what the Victory would look like out of water? --T H F S W (T·C·E) 19:30, 18 January 2011 (UTC)[reply]
Well seeing as the Victory has been "out of the water"/in dry-dock for almost a century, I'd expect that most photographs that exist of the hull are "out of the water". Roger (talk) 20:12, 18 January 2011 (UTC)[reply]
My mistake, I thought it was in the water. Still, that doesn't answer my question: does anyone know where I could find a picture of the whole thing, or an accurate model? I mostly want to see the bottom. --T H F S W (T·C·E) 20:53, 18 January 2011 (UTC)[reply]
I think this site might be helpful. There are a number of reasonably good photos of what appears to be an accurate scale model, particularly this one. Karenjc 21:55, 18 January 2011 (UTC)[reply]
Out of water? Drink rum! Arrrrhhhh. Clarityfiend (talk) 07:37, 19 January 2011 (UTC)[reply]
A centreboard is a useful addition for stability. Trouble is, that article doesn't give much history. I'm personally aware of them being used on some sailing ships of the nineteenth century. HiLo48 (talk) 22:07, 18 January 2011 (UTC)[reply]
Personally aware? How old are you? DuncanHill (talk) 00:06, 19 January 2011 (UTC)[reply]
A centreboard or keel, as I learned earlier here, is mostly to keep the ship in a straight line. Anyways, thank you, the site Karenjc pointed out is exactly what I was looking for. --T H F S W (T·C·E) 00:37, 19 January 2011 (UTC)[reply]
Actually, a centerboard is mostly to keep a ship from drifting sideways with the wind. As a side effect, it does reduce rolling, but it adds little if anything to improve real stability, as it does not significantly change metacentric height. A keel can serve either or both purposes, drift reduction and increasing stability. --Stephan Schulz (talk) 19:35, 19 January 2011 (UTC)[reply]
January 19
Volume (sound)
How did it come to be that Volume became associated with loudness?Smallman12q (talk) 00:09, 19 January 2011 (UTC)[reply]
According to the OED, the first use of the word "volume" to mean loudness of sound occurs in Byron's Werner, 1822: "I heard‥, Distinct and keener far upon my ear Than the late cannon's volume, this word—‘Werner!’". And it was defined in a musical dictionary as early as 1786 to refer to "the compass of a voice from grave to acute: also to its tone, or power". WikiDao☯ 00:40, 19 January 2011 (UTC)[reply]
Recently, a friend had me watch a video of someone putting a candle in a microwave oven and turning it on. This produced some neat effects, supposedly creating "plasma". (The video was not made by professionals.) My question(s) are: Is this actually plasma? And regardless whether it is or not, what exactly is happening?
Avicennasis @ 07:19, 14 Shevat 5771 / 19 January 2011 (UTC)
I have seen such experiments in reality. a flame is already very slightly ionized. Apparently, the microwaves transfer energy to the plasma, ionizing it further and enlarging it, though I don't know the exact mechanism by which this happens. 157.193.175.207 (talk) 07:47, 19 January 2011 (UTC)[reply]
Is there a video online of this anywhere please? 92.24.183.183 (talk) 13:23, 19 January 2011 (UTC)[reply]
It's even more impressive when you do it with a grape. 90.193.232.5 (talk) 14:20, 19 January 2011 (UTC)[reply]
There are many such videos on YouTube. If you can name it, someone has microwaved it, with comic effect. "Coconut in a microwave" isn't as impressive as you'd think, but I remember when I looked for it, I found it.
There is a wide subset of videos about "ball lightning" in a microwave. I think that this is overly promoted - it is simply that fire is conductive and absorbs more energy, and sometimes the gasses continue to glow a moment after they escape from a hole, etc. that has been built for this purpose. I don't think that the sort of energy or structure present in real ball lightning is actually duplicated --- but if someone disagrees, by all means let us know! Wnt (talk) 17:55, 19 January 2011 (UTC)[reply]
Need a Formula
i need information the formula 10extera abrasive becuse used oxalic acid —Preceding unsigned comment added by 85.185.25.251 (talk) 07:30, 19 January 2011 (UTC)[reply]
I think you need to make your question a little clearer. --ColinFine (talk) 08:48, 19 January 2011 (UTC)[reply]
It's not just the brand, but this is the kind of products I'm wondering about.[14] How are they nutrition-wise? Thanks. Imagine Reason (talk) 12:58, 19 January 2011 (UTC)[reply]
I understand the process of freezing damages the cell-structure (water/liquid expanding as it freezes), and then means that when cooked they lose some of their flavour (I know, I've worded that terribly, but have a quick read of the Frozen vegetables article, and I'll have a look for some bette source)... this extract points to the difference in texture between frozen and fresh veg.this source argues that frozen veg are higher in nutritional value than fresh (or, as the case may be, not entirely fresh vegetables). this source also argues that frozen veg are less at risk from contamination, as long as they are not frozen, defrosted and then refrozen - Although, having said that, I am sure that I have seen other sources before that argue that frozen veg in bags that have not been properly sealed are at risk from contamination. Darigan (talk) 13:16, 19 January 2011 (UTC)[reply]
It could also be related to the way they are cooked after being frozen -- are you boiling them in water? I've always found that makes veggies taste a lot more bland. -- JSBillings 13:48, 19 January 2011 (UTC)[reply]
OR answer here: I have found that frozen vegetables taste better when steamed than when boiled; the "steam in the bag they came in" varieties are particularly close to their fresh cousins. Some vegetables take to freezing better than others. I find frozen carrots and frozen corn-on-the-cob to be pale comparisons to their fresh versions, while green beans (haricots) and garden peas are usually fairly comparable. I'm not much of a fan of many cruciferous vegetables in any form, so I can't comment on frozen vs. fresh broccoli or cauliflower or brussel sprouts. --Jayron32 15:48, 19 January 2011 (UTC)[reply]
With peas, it's vastly superior to freeze (or can, though I find canned peas unappetizing) them rather than shipping them "fresh" to a supermarket: the sugar in peas breaks down incredibly rapidly, making it nearly impossible to get good fresh peas, other than by growing them yourself. This is mentioned in Pea#Use, though I'm surprised we don't have anything more on this. I think typically, peas need to be blanched and preserved within a couple of hours of being picked. Buddy431 (talk) 17:15, 19 January 2011 (UTC)[reply]
I think your example of corn is illustrative of a few things. Really fresh corn (as in, you put the pot on to boil while you run out to pick the ears) is unbelievably good; it barely even needs a blanching, you just want to warm it up for the butter. Within a day, it's good, but not nearly the same kind of thing. If you IQF freeze it at that point, you'll get a pretty decent product - good enough that it's better than the so-called fresh corn you find in grocery stores that's already 2-3 days old, if not more. Canned corn is pretty abysmal. So you've got a weird sort of graph where really fresh is best, but frozen is better than just about anything else. The trouble with many vegetables, particularly carrots and peas, is that freezing them wrecks the crispness; the flavour might not change much, but the mouth feel is completely different. Matt Deres (talk) 19:00, 19 January 2011 (UTC)[reply]
IQF seems to mean individually quick frozen in this context - it stops the corn/peas etc from sticking together. CS Miller (talk) 19:37, 19 January 2011 (UTC)[reply]
That's the problem I have with frozen corn: it loses the snappy mouthfeel that makes fresh corn-on-the-cob so tasty. I usually buy my corn at the local farmer's market the day I plan to use it; when it is in season it's usually picked within 24 hours before I buy it. I find all canned vegetables taste more like can than vegetable, so I avoid them pretty much at all cost. --Jayron32 19:23, 19 January 2011 (UTC)[reply]
Wouldn't the vegetables that are used by the frozen vegetables processors be those most manageable for that process? There are lots of varieties of a vegetable. Those destined for freezing are likely to be those that have the handling characteristics that best lend them to mechanical manipulation—from the field to the packaged and frozen product. If any tradeoffs have to be made, taste might get sacrificed in favor of the ease of large scale mechanized agriculture. Even the nonorganic but fresh vegetables on the supermarket shelf might tend to be those varieties of a given vegetable that don't require those qualities that lend themselves so well to the highly mechanized freezing (and harvesting) process but may instead retain some of those qualities that made them desirable in times gone by. Bus stop (talk) 22:23, 19 January 2011 (UTC)[reply]
The one exception, I think, is tomatoes, where the canned ones can have better flavor than either fresh or frozen. Freezing destroys them, and even farmer's markets can't usually handle them at the peak of flavor -- canners, however, can process them directly out of the field. Looie496 (talk) 00:12, 20 January 2011 (UTC)[reply]
I'll second that; canning tomatoes also has the practical effect of concentrating the flavor components. I find good canned tomatoes to be more intensely "tomatoey" than even fresh-off-the-vine-minutes-before tomatoes. Which is not to say that fresh tomatoes don't have their place; canned tomatoes make a better sauce than fresh, but I wouldn't ever use them in a salad. --Jayron32 01:27, 20 January 2011 (UTC)[reply]
Electrical
Hi I have some basic doubts in electrical I am an electrical student please help me
1)Why we maintain voltage as constant not current?
2)In producing AC there comes both +ve AND -ve voltage in both the ends (slip rings) but in power line only phase has while neutral remain null.
3)Is human body a conductor?
4)If a coil connected to power supply produces magnetic flux will that flux link on that same coil and induce a emf?
5)Fan is an inductive load thus on using it there should be 90° phase out b/w Amps and Volt if so won't it affect Transformer?
6)If a bulb excited by AC what happen when it changed to DC of same rms value of volt and current?Kanniyappan (talk) 14:08, 19 January 2011 (UTC)[reply]
Regarding #3, everything is a conductor under sufficient voltage. The human body, being basically a giant bag of salt water (an electrolyte) is actually a pretty decent conductor, even under moderate voltages. Regarding #4, in order to produce an emf through the coil, you must move the coil in relation to the magnet (or visa-versa). Regarding #6, my understanding is that light bulbs (and resistance heaters, and other similar devices) behave roughly the same under AC and DC conditions, as the effects of resistive heating are the same regardless of the direction of the current; in other words the AC or DC nature of the current does not play into Joule's first law. I will let someone who actually knows about this answer the rest (and correct my mistakes). --Jayron32 15:42, 19 January 2011 (UTC)[reply]
It is not possible to maintain a constant current except under carefully controlled conditions. "Voltage" is another name for "electro-motive force" (EMF) which you can compare with "pressure" in water pipes. The supply of both electrical and water services aims to maintain a constant "pressure" so that the amount of electricity or water that flows when something is turned on can be reliably predicted. In the case of water, it is usually the tap that controls how much water flows, but, for electricity, it is usually the resistance or reactance of the appliance that determines how much current flows (though dimmer switches work like taps).
AC supply does not have positive and negative. Usually one side of the supply is connected to earth and for this reason is called "neutral", but it doesn't really matter whether this is done or not except for safety reasons. Both "live" and "neutral" wires behave in exactly the same way (except when one is shorted to earth), so there is really no difference between them if they are isolated from "earth". Three phase supply is generated and transmitted with three "lives", each one being 120 degrees out of phase with each of the others. Sometimes there is no "neutral" (delta configuration), and power can be transmitted without any other conductor. More often, each of the phases is generated at a fixed voltage to a common wire "3-phase neutral" which is usually connected to earth. The three main wires for the three phases still carry the main current because the three currents in the three phases will cancel each other out if they are equal, but the common neutral serves to carry any residual current if the phases are not balanced.
Just one minor addition to Jayron's answer to #4: If AC is connected to a coil, then the flux does indeed produce an induced EMF in the same coil becuase the current is constantly changing. See autotransformer. Dbfirs 18:24, 19 January 2011 (UTC)[reply]
As far as I know, single-wire earth return is never used in the UK. (I've tried it, unofficially, but probably illegally.) Dbfirs 22:17, 19 January 2011 (UTC)[reply]
A/C can have potential on both sides of circuit (although obviously not positive/negative, since it's A/C). Voltage can only be measured as a difference - there is no such thing as an absolute voltage. A/C in households is designed so that the earth is one side of the circuit, and since we stand on the earth, to us the feels like neutral. But it doesn't have to be that way. If you isolate your A/C generator completely from the Earth, then both sides "have" potential (although of course that's meaningless since you need two sides to measure anything). An interesting side effect of this kind of isolation is that you can't get shocked by touching just one wire - you need two to get shocked. Unless of course two different people happen to each touch one wire at the same time and you complete the circuit through both of them via the Earth. You can also make D/C with one side hot and the other neutral - you just need to attach one side to the earth. Ariel. (talk) 22:35, 19 January 2011 (UTC)[reply]
Well if you want to be pedantic, AC does have positive and negative on both sides, it just changes 100 or 120 times each second, so I meant that you can't label either conductor positive or negative. Good point that DC can have "live" and "neutral". Is it often supplied this way (other than in motor vehicles)? Dbfirs 23:09, 19 January 2011 (UTC)[reply]
Most circuit diagrams have a source and ground, rather that a positive and negative. Computer power supplies are also wired this way - a common ground for everything, and different wires for various voltages/rails/polarities. Ariel. (talk) 00:17, 20 January 2011 (UTC)[reply]
Real mains fans have some corrective circuitry to bring the current much closer in phase to the voltage. See power factor. Dbfirs 18:37, 19 January 2011 (UTC)[reply]
Mains supplies provide a constant voltage so that any number of appliances can be connected and disconnected without affecting one another. Each receives the standard voltage and only the total current varies. A constant current mains supply is impractical because the current to an appliance would change every time another appliance was connected, and dangerously high voltage will be delivered if no appliance is connected.
A basic two-wire or "single-phase" AC supply usually has one wire called neutral connected to earth which we may call 0V. The voltage on the other wire alternates between +ve and -ve voltages.
The human body is a conductor. See the article Electric shock.
An emf is induced in a wire in a changing magnetic field. A coil is an example of an inductive load. When a coil is connected to a DC power supply, the current in the coil grows slowly because it produces an increasing magnetic field that induces an emf that opposes the supply voltage. For the same reason, when a coil is connected to an AC supply the current is slow to follow the voltage changes. The time delay can be expressed in degrees where a full alternating cycle is 360. If the coil has no resistance, the current lags the AC voltage by 90.
A fan motor is an inductive load. When the fan shaft rotates the motor is also a generator of emf that opposes the supply voltage.
The filament of a lamp bulb glows because of the heating effect of current flowing through its resistance. The heating power is proportional to the voltage squared (so both positive and negative voltages give heating). An AC supply with rms (root mean square) voltage equal to the voltage of a DC supply has the same heating power as the DC supply. So there will be no change in the lamp brightness if one switches between the two supplies. Actually the brightness flickers at double the frequency of the AC cycles but you cannot see this because mains supply frequency is too high. Cuddlyable3 (talk) 22:59, 19 January 2011 (UTC)[reply]
Rephrased: relaxing voices
Sorry to the board, it wasn't supposed to be a medical question. I will attempt to rephrase the question. Why do some voices, e.g., Bob Ross's, cause people to relax? I've read on other forums that people will watch his show to help them fall asleep. Thank you very much! Reflectionsinglass (talk) 18:54, 19 January 2011 (UTC)[reply]
To answer a question with a question, why is some music relaxing and other music exciting? Why do some people find traffic noises soothing, and others find it irritating? Ariel. (talk) 22:37, 19 January 2011 (UTC)[reply]
Ice expanding, minimum density
It is my understanding that when water is cooled (at standard pressure), it reaches a maximum density at 4°C (due to hydrogen bonds, and then starts to expand as it is cooled further. As it transitions to Ice Ih it expands by about 9%, and then continues to expand as it cools further. At what temperature does ice reach its minimum density? I did a quick websearch and found [15] which indicates that it is at 70K. Is the minimum density really this cold? — Preceding unsigned comment added by Csmiller (talk • contribs) 20:10, 19 January 2011 (UTC)[reply]
Under Ice#Characteristics it says: "The density of ice is 0.9167 g/cm³ at 0°C [...] Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm³ at −180 °C (93 K).", quite the opposite of your statement. But it doesn't say what ice does on further cooling or where minima/maxima of density are. Another image on commons ([16]) also implies that density rises when ice is cooled. Oh, just read through your link again, and as I understand it, ice increases its density when heated up starting from 0K to 70K, then it apparently decreases again--178.26.171.11 (talk) 21:03, 19 January 2011 (UTC)EDIT: The minimum density should be at 0°C then (unless there's a way of "superheating" ice above that without melting it at standard pressure.--178.26.171.11 (talk) 21:05, 19 January 2011 (UTC)[reply]
A very similar question was asked a couple weeks ago.[17]Red Act (talk) 23:23, 19 January 2011 (UTC)[reply]
Allergen
I'm trying to pin down whether an item would be a high risk to cause an allergic reaction. The ingredients listed on the website for it are: Water, denatured alcohol (<5%), sodium iminodisuccinate (<1%), zinc diricinoleate (<1%), cocamidopropyl betaine (<1%), menthol (<1%), microorganisms (<1%), citric acid (<1%), polydimethylsiloxane emulsion (<1%). The microorganisms in this product are non-genetically modified, naturally sourced, non-pathogenic (i.e. do not cause disease) dormant bacteria, and are the primary “active ingredients” in this formulation. They work by eating up all of the accumulated dander, dead dust mites, and dust mite fecal matter that has accumulated in your mattress/ pillows/ furniture/ car upholstery over time, eventually converting those allergens into carbon dioxide and water.
Obviously, people can be allergic to just about anything, but do any of these items seem like likely candidates? Their use of "naturally sourced" bacteria kind of raised my eyebrow, for one thing. I've heard of cleansers touting their "enzymatic action!" before, but not bacterial. Anything else on there look weird? Matt Deres (talk) 20:37, 19 January 2011 (UTC)[reply]
Wow. That's like an ingredient list that includes "...chemicals. All our chemicals are safe, trust us..." To give a parallel example with a more defined set of natural microorganisms, consider the regulation of raw-milk cheeses by the U.S. and Australia. Wnt (talk) 20:52, 19 January 2011 (UTC)[reply]
You also may take interest in the zinc diricinoleate (the basic component there is ricinoleic acid, with two conjugated to zinc. See [18][19][20] for some leads. (It is widely used, but I'd like to know who puts castor oil in chocolate? Remind me to avoid that brand...) Wnt (talk) 21:03, 19 January 2011 (UTC)[reply]
Apparently this is being done by Hershey's, Nestle, and Mars, Incorporated, as part of a campaign to sell cocoa butter to the cosmetics industry and replace it with cheap substitutes in chocolate.[21] Which is just one small reason why American chocolate doesn't taste like chocolate. And people wonder why this country keeps running record trade deficits... Wnt (talk) 04:18, 20 January 2011 (UTC)[reply]
This site: http://www.cosmeticsdatabase.com/ is pretty good for that kind of thing. You can either look up individual ingredients, or register an account and enter all the ingredients of a product and it will give you a grade. (Not just allergies, any kind of potential risk.) Ariel. (talk) 22:52, 19 January 2011 (UTC)[reply]
That site looks helpful - thanks; I'll give it a look when I get some time to play around. I don't know if it matters, but the substance in question isn't a cosmetic, it's for spraying on beds and other furniture to reduce dust mite allergens and odour. Matt Deres (talk) 23:12, 19 January 2011 (UTC)[reply]
Water and brick question
My daughter has a science project in 5th grade this week. I was watching the discovery channel last night and the segament was about taking a 5gal. water jug,filling it a 1/4 with wate, connecting a hose to it,then connecting the end to a hot water bottle.Then take 5 blocks and put them on top of the water bottle.Once that is complete,turn the 5gal. jug upside down about 4ft. high ,then the water should fill the bottle and knock off the bricks. What is the topic of this project? — Preceding unsigned comment added by Jeffryan777 (talk • contribs) 22:01, 19 January 2011 (UTC)[reply]
Can't you ask your daugher? (I added a header) SmartSE (talk) 22:37, 19 January 2011 (UTC)[reply]
The topic appears to be pressure, in that the head of water in the hose is sufficient to lift the bricks. --Tagishsimon(talk) 22:41, 19 January 2011 (UTC)[reply]
You could also discuss conservation of energy. Lifting the 5 gallon jug takes work (in the literal and technical sense of the word). That work is transferred, via the hydraulic pressure, to lift the blocks. One useful property of hydraulic machines is that they can multiply force - so it can be possible to lift some pretty heavy cinder-blocks (which requires a large force), by exerting a smaller force over a large distance to lift the water (hence, to pressurize the fluid). (The force is increased, but the energy is conserved). Nimur (talk) 23:33, 19 January 2011 (UTC)[reply]
And because of this force multiplying, hydraulic systems similar to the one described can act like many types of levers, pulleys and other simple machines. SemanticMantis (talk) 00:02, 20 January 2011 (UTC)[reply]
"Radiation therapy may lower testosterone to the low-normal range in some men" source - so yes. (That could be worked out a lot quicker by googling "radiation lower testosterone") SmartSE (talk) 22:35, 19 January 2011 (UTC)[reply]
Radiation could increase free testosterone but our article on Testicular Cancer does not mention this. Could someone please expand this, as I'm not sure of certain details.--Aspro (talk) 22:38, 19 January 2011 (UTC)[reply]
It depends on what type of radiation, how it was applied, where it was applied, and so on. A lot of research has been performed to study the effects of localized radiation applied to the testes or to the prostate as part of a cancer treatment. Here are some relevant papers on that topic that were found using this Google Scholar search: Effect of Graded Doses of Ionizing Radiation on the Human Testis, Serum testosterone levels after external beam radiation for clinically localized prostate cancer, and so on. If you are trying to evaluate medical options, you should consult a physician. Significant other research has studied the effects of environmental radiation (like if you work in a room or laboratory near radioisotopes, or near a uranium mine, or if you have a radon gas problem in your home); for example, Environmental endocrine disruption: an effects assessment and analysis. We can point you to better resources, and provide better answers if you can specify your question a little more clearly. "Radiation" is a very broad term for a lot of different kinds of energetic effects from a lot of different places: nuclear radioisotopes; strong electromagnetic sources (like mobile phones); and even ultraviolet radiation from overexposure to the Sun or tanning booths. Nimur (talk) 23:45, 19 January 2011 (UTC)[reply]
Plant hardiness - temperature versus sunlight volume
It's about -20C outside these days, though my apartment (apart from near windows) is around 20 degrees at all times. I have a Creeping Charlie that was placed too close to a window and began to die. However, the ambient temperature was never at or below freezing.
This made me wonder about plant hardiness and why some plants cannot tolerate super-freezing temperatures. If a tropical plant like a banana tree was given ample, full-spectrum artificial light but kept at an ambient temperature of 5~10C, would it still die? If yes, why? There wouldn't be any cell damage from freezing... The Masked Booby (talk) 01:14, 20 January 2011 (UTC)[reply]
I don't know, but a conjecture is that different enzymes work best at different temperatures. Perhaps the plants that like warmth have enzymes that only function at those temperatures. Ariel. (talk) 06:16, 20 January 2011 (UTC)[reply]
Yes, it's basically the same reason why humans die if their body temperature is to far away from 37°C (without freezing). The physiology of most life forms is tuned (by evolution) to certain ranges of environmental and internal variables, and if you cross the thresholds, the processes in the cells don't work anymore as they should. That's the same principle for plants, animals and even single celled organisms (some bacteria that thrive in warm shallow sea water won't grow at all or even die in cold shallow sea water, for example). --TheMaster17 (talk) 10:33, 20 January 2011 (UTC)[reply]
This previous question covers some of the relevant points (I was posting as 131.111). Chilling can damage plants because it disrupts the cell membranes by making them solid, instead of fluid which then makes them leaky, allowing all the parts of cells to mix, whcih is not good news at all. A banana plant will certainly die at 5-10C because they have never evolved to cope with those temperatures. Ariel's point about enzymes is probably partially true, but the disrupting of cell membranes is more of an issue - unlike us, plants have to cope with a wide range of temperatures and so they have enzymes which function over wider ranges, or will have isozymes for different temperatures. As to how some plants survive super-freezing, it's pretty complicted! There are some details at Ecophysiology#Temperature (unfortunately unreferenced, but I can vouch for its accuracy as I wrote it from lecture notes - I will try to reference it some day!) and combined these allow trees like larch in Siberia to survive liquid nitrogen, because the cells are placed in suspended animation. If you want a paper discussing this, this one might be a good start. SmartSE (talk) 15:43, 20 January 2011 (UTC)[reply]
Pregnancy and radiation-blocking smocks...
Here in China pregnant women wear smocks with a thin lead liner in the workplace. I can understand the need for such clothing if someone worked in an area with serious radiation potential, like an x-ray equipment factory or something. However, 99% of these women only ever sit in front of a computer doing routine tasks. I suspect this practice, like many medical habits in China, is based on no real proven science. Is there anything to gain from such clothing? I didn't see any indications in the Electromagnetic radiation and health article... The Masked Booby (talk) 01:17, 20 January 2011 (UTC)[reply]
Well, considering that lead doesn't even block EMF I don't know what they're trying to achieve. I would be much more worried about exposure to lead! Even if it is sealed, what if a section becomes exposed due to wear or tear? Lead rubs of extremely easily onto hands or clothes, even just touching it and then handling food or inadvertently touching your mouth sounds like a much higher risk then sitting in front of a computer or monitor. Vespine (talk) 03:35, 20 January 2011 (UTC)[reply]
I'd hesitate to concur -- while lead doesn't attenuate all forms of electromagnetic radiation well, it does do a great job for x-rays, for example. This may not relate to the circumstances posed in a positive fashion (it may reveal the ignorance of Chinese women and/or their husbands), but your blanket statement is certainly incorrect on the whole. DRosenbach(Talk | Contribs) 05:02, 20 January 2011 (UTC)[reply]
EMF |= electromagnetic radiation. I didn't think computers and lcd monitors are significant sources of EMR, unless you have a wifi or bluetooth transmitter or something. It's hard to find reliable sources to look this up because of all the fear mongering but my guess is there would be small amounts of things like radio waves and stuff coming out of a normal computer, but there's certainly no ionizing EMR coming out of your computer. Vespine (talk) 05:24, 20 January 2011 (UTC)[reply]
It could have started with ladies worried about the X-Rays emitted from older model CRTs (Which, for all I know might still be in wide use in China.). Once these sorts of things start they usually become divorced from their rational underpinnings pretty quickly, so it's not hard to imagine that some ladies would still wear them even if they never use anything that emits anything dangerous. APL (talk) 15:30, 20 January 2011 (UTC)[reply]
Biology vs. the Cosmetics Industry
(My last question of the day...) My wife, like many women, spends a fair bit of money on facial cleansers and moisturizers, always used in conjunction. She also makes a big stink about my need to have empty pores on my face in order to be "clean". I am skeptical of this entire process. I've read Cleanser, Sweat gland, Acid mantle, and Sebaceous gland and have not been able to definitively confirm or refute my contention that: stripping oil from your face with cleansers and then applying moisturizer is equivalent to doing nothing at all and letting your skin regulate itself, it just costs loads more. But again, none of those articles directly say whether this is truly necessary or not. Can anyone shed some scientific light on this? The Masked Booby (talk) 01:28, 20 January 2011 (UTC)[reply]
We have a refdesk rule about medical diagnoses, do we need one about marital harmony? Ariel. (talk) 01:33, 20 January 2011 (UTC)[reply]
This is not a medical diagnosis request. This is a question about the biological/chemical function of the face and the utility of cosmetics. I am inherently distrustful of the cosmetics industry given their proven non-sense like conditioner making your hair "healthier" and would like to know if facial cleanser/moisturizers fall into the same sphere. I included the bit about my wife for color, not because I'm going to print out your replies and wave them in her face and say SEE! WIKIPEDIA SAID SO! The Masked Booby (talk) 01:38, 20 January 2011 (UTC)[reply]
Stuff in small print is usually for more light hearted (or off topic) comments. Ariel. (talk) 01:42, 20 January 2011 (UTC)[reply]
You aren't just stripping the oil off of your face, you are stripping all of the stuff that tends to get stuck to the oil, like dead skin cells, dirt, (for many women) makeup, etc. It may be quite difficult to remove, for example, dead skin cells from pores with just soap, while an astringent cleanser which dissolves the oil the skin cells are stuck to will make it much easier to get them out. Bacteria like to feed on these dead skin cells; this can be a primary cause of acne. The deal is, since you just removed all that oil, you need to replace it to prevent your skin from drying out, hence the moisturizer. In summation, it isn't the skin oils per se that need removing, its all of the stuff that is in the oil. --Jayron32 01:37, 20 January 2011 (UTC)[reply]
I guess the question is, Does that stuff really need removing? Where is the science behind it? (PS: Agree with comment about marital harmony.) HiLo48 (talk) 02:52, 20 January 2011 (UTC)[reply]
Which is a fair question. I'm more familiar with the argument against shampoo-conditioning, which is a somewhat similar arrangement: the hair is cleaned of oil (and the attached dirt) and then has a moisturizer (hair conditioner) added back on. Our article on that argument can be found at the humorously titled "no poo", though it's a pretty poor article. Western habits (and obviously Chinese ones as well) on cleanliness are hugely influenced by social expectations, to the point where the "necessity" of having to shower multiple times a day, for example, borders more on ritual purification than anything to do with an increase in health or other objective goal. As with anything else, moderation is probably the sensible option. Matt Deres (talk) 03:02, 20 January 2011 (UTC) Quick aside - I got a chuckle by reading that our article on cleanliness has been flagged for "cleanup" for seven months... [reply]
@HiLo48 for some people, probably not, but for others definately. I am a life-long sufferer of acne (I basically have the exact same skin problems at 34 that I had at 14); through years of trial and error I have found that some products work for me, and some do not, and I use those that do. Clearly, for people who have acne, skincare can be tricky business. It's one of those "if you don't have the problem, you just don't understand" sort of deals. For people without acne problems, washing daily with the bar soap they use for the rest of their body works fine. For others, however, it just doesn't cut it. --Jayron32 03:35, 20 January 2011 (UTC)[reply]
I seem to remember discussing something similar about washing hair too, but can't find an archive link. If you're correct, it almost certainly has something to do with differences in skin flora. I found this which says "soap may reduce the normal skin flora, leading to an increased colonization of the skin with coagulase-negative staphylococci; this effect has been linked to the shift in skin pH caused by soaps. Lastly, it has been found that applying agents that specifically inhibit gram-positive cocci, such as antibacterial soap, generally increases gram-negative rods." and this paper tells a similar story. I think it's probably difficult to give you a definitive answer and as everyone else is ORing so will I - I think that cleansers + moisturisers change the balance of skin flora and that if you then stop using them, your skin condition detiorates because the equilibrium was being maintained by the products. For those of us who don't use such products (myself included) our skin flora is in equilibrium, and generally speaking we don't suffer from unhealthy skin. Carrying on, we obviously evolved in a world without soap, and our skin produces oils for a reason, I see no reason why you would need to replace this with something else. (Maybe you can experiment with your wife's face, only letting her clean + moisturise one side and come back with photos in a few months) Interestingly, I don't think anyone has done any metagenomic studies of skin flora, which would be a very interesting thing to do, when comparing you and your wife. SmartSE (talk) 16:12, 20 January 2011 (UTC)[reply]
What about situations where skin flora is "off" in the absense of products, but correctly balanced with them, before such products were used by the person? I had acne before I started using products... Your explanation isn't consistant in that skin problems exist in absense of even the existance of skin care products. It would only make sense if skin problems didn't exist prior to people using skin care products. However, that is demonstratably false. --Jayron32 16:29, 20 January 2011 (UTC)[reply]
WP:OR Face wash products work well. They just include sticky substance which once applied to your face you must wash your face thoroughly with lot of water to remove it, and any other dirt/oil on your face, if any, also washes out along with the water :) - manya (talk) 04:10, 20 January 2011 (UTC)[reply]
Calcium oxide reaction
calcium oxide reaction with water —Preceding unsigned comment added by 125.99.5.139 (talk) 09:08, 20 January 2011 (UTC)[reply]
Welcome to Wikipedia. You can easily look up this topic yourself. Please see calcium oxide. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. . DMacks (talk) 11:04, 20 January 2011 (UTC)[reply]
Is there anybody to reply me positively117.194.164.185 (talk) 14:35, 20 January 2011 (UTC)
1.Is a photon massless?
If yes,then why does it has particle nature as a particle has a must property of mass and it also has momentum?
If no,then why it cannot be proved?
2. Is a vacuum really vacuum or not?
If yes,then why does there exist a dark energy as energy cannot be held without any medium?
If no,then what does there exist?
3. Does a string really exist?
If yes,then what is the matter the string made of?
If no,then what is the cause of producing charge in an electron?
4. Do the photons carry the energy from one place to another?
If yes,then why does the intensity of radiation decrease gradually and if an electro magnetic radiation is one kind of transverse wave,then the main property of this kind of radiation should be transfer of energy not the particle and it definitely needs a medium to traverse?
5.What is the situation before the Big Bang? Is it a cyclic process?
6. What is the way to transfer energy from one place to another?
If it is vibration of different mode which produce different kind of energy,then is it possible to construct the T.O.E. equation?
(I think I have some definite reasons to explain those things stated above. But I need a definite person to explain these mathematically. — Preceding unsigned comment added by 117.194.164.185 (talk • contribs)
You asked a lot of very hard questions, so it is impossible to answer them all here. You should look at the articles on Wikipedia and ask if you have specific questions.
1. A photon has no rest mass, though it does have momentum. Who says that particles must have mass? It's perfectly possible to conceive a massless particle.
2. Vacuum#In_quantum_mechanics and Vacuum energy explain this better than I could. The exact nature of a vacuum is complex - however it is quite well defined in quantum theory. The idea that energy cannot be held without a medium is just a hypothesis and may not be true.
3. String theory is still a matter of debate, and it's not clear if any version of it is true. Therefore nobody is certain what the strings are made of, or even if it makes sense to ask if they are made of anything (just as Einsteinian space-time is not made of anything, and electrons are, in standard models, made of electron without any internal structure).
4. Photons do indeed carry energy. Intensity of radiation decreases with distance from the source because photons spread out as they travel and the further from the source you are, the fewer photons hit you (see inverse-square law).
(edit conflict)Almost identical to previous response, but I've written it now and don't want to discard it.
1. If you mean "does a photon have zero rest mass ?" then the answer is yes, although the question is somewhat meaningless as a photon is never observed at rest. This does not prevent a photon being a particle.
2. If you mean "is the vacuum empty" then the answer is no - any vacuum in our universe will contain the electromagnetic field, its quanta (photons), a large number of passing neutrinos and a "sea" of virtual particles.
3. If you mean the strings in string theory then we don't know whether they really exist.
4. Yes, photons carry energy. The intensity of radiation decreases with distance because the flux of photons per unit area decreases as the area over which the photons are spread increases. For large photon fluxes the intensity appears to follow a continuous curve; for small photon fluxes the continuous model breaks down and individual photons are observed. You can recover the continuous model by averaging the photon flux over a long enough period of time.
5. We don't know what was before the Big Bang. We don't even know if this question makes any sense.
6. In quantum field theory, you can think of energy as being carried by waves in quantum fields or by the momenta of particles associated with those fields. These are dual models - "reality" is both, not one or the other. A field does not need a medium. Gandalf61 (talk) 15:40, 20 January 2011 (UTC)[reply]
@OP: Regarding 3: What does "really exist" mean? String theory is a model just like many other models. It is useful insofar as it matches observations, and has a useful predictive power. Is an electron a little ball, a standing wave, a probability distribution? It is all of these, depending on which model you use. None of this is wrong, though some models better match observation, and some are more useful in certain applications. Is light a wave or a particle? Neither, it is just light, but we have wave-based models of light which are useful in some explanations (see diffraction, refraction, etc) and we have particle-based models of light useful in others (see photoelectric effect). If you commit yourself to "The Truth" rather than "Consistent with observations" you miss the point of science. It is perfectly fine and consistant to have multiple, accepted models of the same phenomenon, and each of these models is "real" insofar as any can be. So, stop worrying about if strings "exist" or what they are "made of" and instead focus on what the model teaches us about how the universe works. --Jayron32 16:00, 20 January 2011 (UTC)[reply]
It remains to be seen whether or not string theory is a useful model of reality capable of offering testable predictions. In this context, showing that string theory is capable of making new verifiable predictions is basically the same as showing that strings "really exist". Dragons flight (talk) 16:28, 20 January 2011 (UTC)[reply]
That's kinda the point; though it would be better to say that "really exist" misses the boat in that it implies only a single "right" answer; after all if strings really exist, than other models which do not contain strings, really don't exist. Having a paradigm that searches for the One Right Answer completely misses the point of science. Lets go back to the light example. Does light really and truly exist as a particle or does it really and truly exist as a wave? If you commit yourself to that mindset, you are left with three very unsatisfying results:
Light is only one or only the other (observationally inconsistent; light clearly behaves like a particle in some situations, and like a wave in others)
Light is both at the same time (logically inconsistent; a little ball and a mode of movement don't occupy the same class of nouns even. It's akin to claiming that something smells like the color red. It has a poetic appeal, but it doesn't make any logical sense)
Light switches between the two modes, depending on the type of observation (seems better at first, but it begs the question about what light is doing when it isn't being watched.)
People have grappled with this concept for a very long time, the only satisfying result comes when you come to realize that there is a difference between reality and perception, and most importantly reality is not observable at all at the most fundemental level. All you can say is that your mind perceives an object or phenomena to be real, but you have no way to confirm that. Look at your keyboard. How can you confirm your keyboard exists, as an entity seperate from your internal, mind-created construct of what it is. At some point, you need to accept that as true. But that's still an unproven (and unprovable) proposition. When we deal with scientific concepts which are only observable in the second or third order, where we are further removed from the observable properties of it, these sort of problems become manifest in the situation. Back to light, rather than trying to decide what light "really" looks like, and "really is", change your paradigm to just accept that light is what it is, and is fundementally unconcievable apart from the models we make to describe it. Accept that, while light exists and is consistent, our models being by definition imperfect representations, can never fully capture what it means to be light, and let yourself be OK with that. Understand that the two competing and mutually exclusive models of light work in their own domains, are uncontradicted by other models, and so are as close to "real" as we can get, insofar as anything is "real". On that level, string theory may be "real", but also be willing to accept other, competing, and apparently mutually exclusive models as equally "real" insofar as they contradict neither logic nor observations. --Jayron32 16:48, 20 January 2011 (UTC)[reply]
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