Wikipedia:Reference desk/Archives/Science/2007 November 12

= November 12 =

Seriously hurt in the news
We frequently hear in the news that somebody has been "seriously hurt", or even worse "herido muy grave" or the worst "en estado crítico" (I don't know how you would say that in English, normally somebody who is in "estado crítico" dies soon). What do those expressions mean in medicine? --Taraborn 00:35, 12 November 2007 (UTC)
 * See Medical conditions. These labels are used by hospitals when speaking to the press and are not used among doctors. They vary in meaning from hospital to hospital. --Milkbreath 00:49, 12 November 2007 (UTC)
 * Proving once again that WHAAOE. (But, dang, Milkbreath, ya beat me to it. *I* was just about to post that link!) —Steve Summit (talk) 00:56, 12 November 2007 (UTC)
 * Thank you, guys. --Taraborn 01:07, 12 November 2007 (UTC)
 * I think what you call "en estado critico" is, in english, "in critical condition". Just an FYI. Kuronue | Talk 21:06, 13 November 2007 (UTC)

Jupiter's moon Io
Is there a certain reason Io has volcanoes? —Preceding unsigned comment added by 72.38.227.206 (talk) 00:35, 12 November 2007 (UTC)
 * Well, I guess the answer is only really stated clearly in the very first paragraph of Io...you couldn't be expected to find something buried that deeply! SteveBaker 01:36, 12 November 2007 (UTC)
 * tidal stress-- ( Mulligan's Wake ) (t)  01:37, 12 November 2007 (UTC)
 * I think that prior to IO being surveyed by the Vikings during the 70s, it was just assumed that small remote planets and satellites would all be frozen solid. The incredible phenomenon of IO suggests there could be life-friendly worlds far away from their host stars. Not IO, however. It is estimated that there the entire surface is continually subducting from the heat of tidal friction and is completely renewed every hundred years or so. Myles325a 03:49, 14 November 2007 (UTC)
 * Jeez! Those Vikings discovered everything!  -SandyJax 16:49, 14 November 2007 (UTC)

stpm trial exam question
can ketone react with chlorine?thank you —Preceding unsigned comment added by 218.208.91.249 (talk) 02:04, 12 November 2007 (UTC)


 * Perhaps haloform reaction may be of some help. (EhJJ) 03:11, 12 November 2007 (UTC)

"brush harder, not smarter"
my dentist told me this. what does he mean? —Preceding unsigned comment added by 172.130.26.74 (talk) 02:08, 12 November 2007 (UTC)


 * Why don't you ask him?
 * The usual exhortation is to do something smarter, not harder -- that is, to do it with more care and deliberation, and less brute force. —Steve Summit (talk) 02:16, 12 November 2007 (UTC)
 * As Steve has pointed out, the usual phrase is "do it smarter, not harder". In this case, your dentist may be using a play on words to imply that you are not brushing hard enough. If you're not sure, you may want to ask him. (EhJJ) 03:14, 12 November 2007 (UTC)
 * You might be remembering it backwards, or your dentist might have said it backwards accidentally, or your dentist might have said it backwards intentionally. There’s no way we can know which is the case; you’ll really need to ask your dentist.  MrRedact 07:50, 12 November 2007 (UTC)
 * Your dentist wants you to brush gently (not harder), and with a technique (smarter) that gently cleans effectively. If you use a hard brush and scrub, you'll damage your teeth and irritate your gums.  If you gently massage your gums with a soft-bristle brush, and hold the brush at the right angles, you will prevent gum disease.  --Mdwyer 20:40, 13 November 2007 (UTC)

It means that either you or your dentist are dyslectic. Myles325a 03:51, 14 November 2007 (UTC)

Bamboo nomenclature
72.50.180.145 03:54, 12 November 2007 (UTC)After reviewing your article on bamboo, I'm not sure what you call stalks of bamboo. Are they called stems? I've heard them called that before. Are they called branches? Are they called culms? which according to wikipedia- "originally referred to a stem of any type of plant". What is the appropriate scientific way to name them, because I'm confused.


 * A bamboo's shoot is like a tree's trunk, whereas a bamboo's stem is like a tree's branch. A culm is a stem of a monocotyledon, which bamboo is an example of.  Someguy1221 05:06, 12 November 2007 (UTC)

Laxative agent in apple juice that's not in pear juice?
Here's the strange thing: I get diarrhea when drinking apple juice. Even a single glass causes discomfort, and multiple are certain to cause diarrhea (which passes quickly, however). I thought this could be oversensitivity to sorbitol, but I have no problems drinking even large amounts of pear juice, which likewise contains sorbitol. Ditto for any other fruit juice you'd care to name (though I haven't tried prune juice). I have no problem with raw apples either. It could be an additive of concentrated apple juice (I haven't tried "natural" apple juice either), but I wouldn't know which one.

Though apple juice really is the only thing giving me problems (so it's easy enough to avoid), I'm curious if anyone could guess what could cause diarrhea and is just about only found in (concentrated) apple juice -- a rare chemical or ratio of something? 82.95.254.249 07:57, 12 November 2007 (UTC)


 * Apples have traditionally "gone through" some people, especially if the apples are the first of the season. I suspect it may be malic acid that causes this, but I stress this is pure speculation. DuncanHill 14:24, 12 November 2007 (UTC)


 * Well, any hint is welcome, but I don't think it's malic acid. Tart apples are my favorite, actually, and I have no problem with other foodstuffs that contain malic acid (according to the page). 82.95.254.249 20:10, 12 November 2007 (UTC)


 * I'd take another look at Sorbitol. It has known laxitive effects (many sugars do).  As for the difference between pear and apple juice, I can only speculate.  Apples and pears are VERY similar.  It is possible that the pear juice has been modified in some way?  Perhaps it was pasteurized or cooked in some way that would have converted its sugars? --Mdwyer 20:37, 13 November 2007 (UTC)


 * I get a little stomacheache from eating an apple core, and also from fresh apple juice made from whole apples. I deduce that the core or seeds has something in it that disagrees with me but not the majority of people. I am vaguely aware that apple leaves are supposed to contain some poison also.Polypipe Wrangler 22:10, 13 November 2007 (UTC)


 * Apple seeds do contain a small amount of a cyanide compound. Snopes has the dirt on it. --Mdwyer 03:44, 14 November 2007 (UTC)

Pseudo-stable isotopes
For isotopes with half-lives longer than the known lifespan of the universe, such as Calcium-48, how do they determine that the isotopes aren't stable? --67.185.172.158 08:06, 12 November 2007 (UTC)
 * Simple: get a lot if atoms of that isotope and wait for them to decay. Remember that half-life is a statistical property: a half-life of X doesn't mean that no atoms will decay until X has passed. An unstable atom can decay at any time (which is exactly why we talk of "half-life" and not the full life).
 * The initial suspicion that an isotope is unstable comes from theoretical considerations, and obviously it's hard to determine the half-life for an extremely long-lived isotope with great accuracy. 212.178.108.2 10:55, 12 November 2007 (UTC)


 * In that case, the article cited in footnote 2 explains it. They thought it was a likely candidate (via theory) for a very rare form of decay, and then spent a lot of time watching it in a test chamber (via experiment) to see if it actually did decay in that way. And it did. Hooray. --24.147.86.187 17:00, 12 November 2007 (UTC)


 * A radiation counter can pick up a single atomic decay (so long as you shield it from background radiation) - if you have a mole of whatever isotope you have then you have 6x1023 atoms. A mole is the atomic weight expressed in grams - so a mole of a solid or liquid is a pretty reasonable quantity to measure.  The age of the universe is something like 4x1017 seconds - and a mole is 6x1023 atoms - so in half the age of the universe, you'd expect 3x1023 radioactive decay events - so you'd expect about half a million decay events per second.  Easily detectable!  More to the point of course, if this is a synthetic isotope (made in a nuclear reactor for example) so that it's "fresh", it'll be radiating a lot more than it will be when it's reached it's half-life.  SteveBaker 18:51, 12 November 2007 (UTC)


 * For "a lot more" read "twice as much".


 * Calcium 48 makes up only 0.187% (1/535) of the atoms in natural calcium, so making a whole mole of the stuff (about 48 grams) would be rather expensive. And then, its half life is not a mere 4x10^17 seconds, but about 100 times that.  But all this just means that the number of decay events you'd have to detect is smaller, not that there are too few to detect at all.  No doubt the paper by Balysh et al., cited in the article, would have details of how large a sample was used and how long it was observed. --Anon, 23:26 UTC, November 13, 2007.

Penguins in the Arctic? Polar bears in the Antarctic?
Just checked the articles on Penguins and Polar Bears. Just wanted some confirmation, are there any penguins that live in the Arctic? Also are there any Polar bears in the Antarctic? 64.236.121.129 14:20, 12 November 2007 (UTC)
 * No, and no. DuncanHill 14:22, 12 November 2007 (UTC)
 * But they could live there, couldn't they? I mean, if you kidnapped some and dumped them there, they'd manage ok, wouldn't they (not that I advocate kidnapping well dressed animals or anything)? Jeffpw 14:44, 12 November 2007 (UTC)


 * No - Penguins are almost 100% confined to the southern hemisphere (they do creep just above the equator - but not by much) - but not all species live in snow and ice - some are very happy in the tropics. Polar bears are strictly Arctic.  Whether you could transplant them depends on an awful lot of things.  Bears live on the mainland as well as in the arctic ocean - if you dumped them in the antarctic, they'd have no way to make it do warmer areas in the winter - also the species they are used to hunting would not be present.  Some penguins have these very complicated behaviors where one sex gathers together far inland to look after the eggs while the other partner goes off for food.  It's not clear how this would work in a continuously moving sea of ice floes - do penguins navigate somehow?  I'd be quite surprised if relocating either species would actually work out well. SteveBaker 15:03, 12 November 2007 (UTC)


 * The polar bears would probably eat the penguins. Seriously.  The kind of penguins that live in Antarctica generally are unable to recognize any land animal as a predator, because the only land animals that have ever attacked them in the last million years or so have been humans or escaped domesticated animals like dogs.  If you took a polar bear to the Antarctic, the polar bears would very quickly gravitate towards this huge, meaty, docile food source.  If you were to transplant some penguins to the Arctic, then even if they could solve the problem of figuring out which landmass to lay their eggs on, eventually the polar bears (which will eat any kind of animal if they're hungry enough) will figure out that they're easier to catch than their usual prey, and kill them off in short order.  --M @ r ē ino 18:54, 12 November 2007 (UTC)


 * Well, the penguins are prey to Leopard seals and killer whales - so they have seen large predators - just not big, furry white ones. It's hard to know what their reaction might be.  Certainly they are generally unafraid of humans.  (True story: When my kid was about 5 years old, we went to SeaWorld, saw the Shamu show and then visited the Penguin enclosure for a behind-the-scenes tour.  My son (who happened to know a lot about penguins) picked the moment with the most other people around to proudly (and loudly!) announce that "Shamu is a killer whale - he likes to eat penguins!" - the penguin-keepers were torn between their roles as "teaching kids about nature" and "being good corporate employees" - so simultaneously, one of them said "Yes, that's right!" and the other one said "No, Shamu is friendly with EVERYONE!" - then each of them realised their horrible blunder and changed their story - it took them quite a while to decide what story line was the best and lamely trot it out.  It was hilarious!)  SteveBaker 21:06, 12 November 2007 (UTC)
 * I will gladly concede that penguins face aquatic predators (and avian predators) -- just not land-based predators. --M @ r ē ino 21:25, 12 November 2007 (UTC)

Wrinkled face
Is there an illness that makes the skin wrinkle excessively? Keria 17:04, 12 November 2007 (UTC)


 * There is evidence that smoking can do that to you. SteveBaker 18:39, 12 November 2007 (UTC)
 * I'll point out that our article on Wrinkles sucks, so this question might require some real digging. --M @ r ē ino 18:57, 12 November 2007 (UTC)


 * As far as I know, wrinkling of the skin is caused by old age, however certain skin disorders may contribute to wrinkles too. Topical Corticosteroids as often used by Eczema sufferers are notorious for thinning the skin and this can definitely cause premature wrinkles. GaryReggae 22:41, 12 November 2007 (UTC)

As the piccie in Wrinkle article demonstrates, masturbation makes wrinkles a lot, lot worse. Myles325a 22:51, 12 November 2007 (UTC)

We must have a few doctors on the science desk, a dermatologist who would like to add a "disease" section on the article wrinkle? Keria 02:55, 13 November 2007 (UTC)

There is a wrinkly skin syndrome, but the description seems to indicate that the wrinkly skin is not on the face. --JWSchmidt 03:55, 13 November 2007 (UTC)

medical ebooks
i am a 2nd year mbbs student of osmania medical college.please give me information about sites to download medical ebooks,so that i can clear evrything. —Preceding unsigned comment added by 117.97.30.240 (talk) 17:13, 12 November 2007 (UTC)

You could try our sister site [Wikibooks] although I don't know if there is anything medical there. Chances are if it's anything too specialist, the best option (apart from spending extortionate amounts of money on textbooks) is a visit to your local library. GaryReggae 22:39, 12 November 2007 (UTC)


 * Try www.freebooks4doctors.com. - Cybergoth 03:16, 16 November 2007 (UTC)

how does our organism recognize foreign tissue?
How can our organism distinguish between our own tissue and foreign ones? Of course, the DNA is different, but how our immune system can know it? —Preceding unsigned comment added by 80.58.205.37 (talk) 18:28, 12 November 2007 (UTC)
 * Mainly due to Antigens. These are molecules on the outside of cells, and they are distinctive to each type of cell. For example, there are 2 two types of blood antigen (A and B), so someone with blood type A has "A" antigens on their blood cells. If you give these to someone else whose blood is also A (or AB), the body accepts it, while if you give it to someone of blood type B, the body can't recognise the blood antigens, so it attacks the blood, which causes all kinds of nasty effects inside the body. Laïka  18:50, 12 November 2007 (UTC)


 * See also, here: "To be able to destroy invaders, the immune system must first recognize them. That is, the immune system must be able to distinguish what is nonself (foreign) from what is self. The immune system can make this distinction because all cells have identification molecules on their surface. Microorganisms are recognized because they have unique, foreign identification molecules on their surface. In people, identification molecules are called human leukocyte antigens (HLA), or the major histocompatibility complex (MHC). HLA molecules are called antigens because they can provoke an immune response in another person (normally, they do not provoke an immune response in the person who has them). Each person has unique human leukocyte antigens. A cell with molecules on its surface that are not identical to those on the body's own cells is identified as being foreign. The immune system then attacks that cell. Such a cell may be a microorganism, a cell from transplanted tissue, or one of the body's cells that has been infected by an invading microorganism." Rockpock  e  t  18:52, 12 November 2007 (UTC)

Potassium chloride and seeds
Is potassium chloride a fertilizer like potash, or a toxin like chlorine? How it will affect the growth of seeds? 199.89.180.65 18:37, 12 November 2007 (UTC)


 * The majority of the potassium chloride produced is used for making fertilizer.  Just remember that it might kill your livestock if they eat a bag of it.  --M @ r ē ino 19:00, 12 November 2007 (UTC)

Mobile phone buzzing
What's the buzzing/beeping that speakers make just before a mobile phone rings? I can't imagine the phone is making an electric/magnetic field strong enough to affect speakers from 3+ metres away. And if it is, is it safe to keep it near my computer? Laïka 18:45, 12 November 2007 (UTC)


 * Don't worry about it. My cellphone does that to the earbuds on my MP3 player and my FM clock-radio - it's simply the phone acknowledging the cell tower prior to ringing the ringer.  The radio signal from the phone is plenty strong to induce a current in a wire of a suitable length to act as an antenna.  It should be OK to keep it by your computer - the voltage is enough to hear on a speaker because they are analog devices - also loudspeakers and headphones have long wires leading to them that make great antennas.  But no, it won't affect your computer (except that you might hear it on the computer's speakers). SteveBaker 20:55, 12 November 2007 (UTC)


 * Yes, this is very common although some speakers appear to be sensitive to this and others not - depending on whether the cable is shielded - otherwise the cable will act as an aerial and pick up the electromagnetic waves! It won't do any harm though, other than the obvious interuptions to your audio. GaryReggae 22:37, 12 November 2007 (UTC)


 * It occurs to me that there is an easier way to explain this convincingly. I should point out that inside the phone is a small computer - you know it survives the most intense radio signals the phone can put out without screwing up.  What's more, radio signals decrease in strength as the square of the range.  The computer in the phone is at most maybe 2cms from the radio transmitter.  So if you put your phone maybe 20cms from your desktop computer, the signal strength will be 100 times less.  If the computer in the phone can take the full strength, then for sure your desktop machine will be OK with just 1% as much radio interference. SteveBaker 23:42, 12 November 2007 (UTC)


 * Also, a desktop computer usually has a metal case (with few holes), so the electromagnetic waves most probably can't get in it. This doesn't apply to notebook computers of course.  &#x2013; b_jonas 11:21, 13 November 2007 (UTC)


 * Note that this only happens with TDMA (especially current-generation GSM) phones. You aren't hearing the signal itself, so much as the signal being turned on and off something like 50 times per second.  This induces currents in some analog circuits -- especially inexpensive amplifiers that lack correct shielding.  --Mdwyer 20:34, 13 November 2007 (UTC)

A designer wishes to calculate the thickness of a steel cable for suspending a passenger lift
The total length of cable supporting the lift when it is at the ground floor is 8 m. The mass of the lift when full of passengers is 950 kg. The designer has decided to incorporate a safety factor of 10 into the lift cable: i.e., the cable must be able to withstand 10 times the load it will actually be exposed to in service, before it fails. The steel selected for the cable has a failure stress of 900 MN m– 2. (a) Using this information, calculate the required diameter of the cable. Show all your working. Assume that the cable is a single piece of steel, with a circular cross-section. (Ignore any effect of the weight of the cable in your calculation.) The downward force F on the cable is calculated by multiplying the total mass m (expressed in kg) by g, the acceleration due to gravity: F = m × g Take the value of g to be 10 m s–2. (In reality there is extra force needed to accelerate the lift upwards, but as this is relatively small, there is no need to consider it here.) Hint: the safety factor means that the cable will fail – the stress will reach its failure stress – when it is loaded to 10 times the intended design load. Use this to calculate the cross-sectional area of the cable, and so its diameter. I found the diameter to be between 11 and 12 mm —Preceding unsigned comment added by Flano1 (talk • contribs) 19:09, 12 November 2007 (UTC)
 * So do I. 169.230.94.28 19:23, 12 November 2007 (UTC)


 * This does sound a bit like a homework question to me ("Show your working" is always a dead giveaway!) - please look at the top of this page where you'll see it's our policy not to help people with homework. Sorry.  If there is any specific part of the math/physics you can't understand, then feel free to ask specifically about that problem and we'll be more than happy to assist. SteveBaker 20:50, 12 November 2007 (UTC)


 * It looks like you have all the information you need here to calculate the answer. The most obvious thing to do is ignore the factor of ten for the moment, work out the diameter of cable needed just to support the normal load then multiply it by ten.  Our page on Elevators may be of use. GaryReggae 22:34, 12 November 2007 (UTC)
 * Erm...cough...no, no, NO! Cable strength is proportional to cross-sectional area - not diameter.  To get a factor of 10 safety factor, you only need to make the cable sqrt(10) times thicker.  About 3.16 times thicker should be fine. SteveBaker 00:01, 13 November 2007 (UTC)
 * Using the fracture strength of the cable, instead of the yield strength, sounds like a bad idea as well, particularly for applications involving lifting humans... Tito xd (?!? - cool stuff) 00:13, 13 November 2007 (UTC)

Percent solutions
While interviewing undergraduates to be a lab helper, our lab manager was bemoaning how every single candidate could not explain how to make a molar solution. She then asked one how to make a 1% percent agarose solution [weight/volume] and the hapless student suggested filling a measuring cylinder to 1ml with agarose then filling it up to 100ml with water. After we were done laughing at his expense, I noted that doesn't bode well for the future of American science, as it should be simple to work that one out by logic. But this got me thinking that might not actually be the case: a percentage solution [w/v] is considered to be 1g in 100ml. But logically, it should probably be 1mg in 100ml. Are the w/v units different simply by convention, or is there a logical explanation? Rockpock e  t  19:16, 12 November 2007 (UTC)


 * In CGS (centimeter, gram, second) units, the base unit of mass is the gram, while the 'natural' unit of volume is the cubic centimeter (equal, of course, to one milliliter). So you shouldn't be deceived by the 'milli' prefix; what you should be thinking is 1% (w/v) is 1 gram in 100 cubic centimeters, which just happens to be 1 gram in 100 mL. TenOfAllTrades(talk) 19:42, 12 November 2007 (UTC)


 * It’s ultimately only a guess, but I don’t think the name "percentage solution" was originally perceived to be a good name for what it means due to how it works out in CGS units, but rather due to the density of water, which is by far the most common solvent. 1 ml of water weighs almost exactly 1g.  (Indeed, the gram was originally defined to be the mass of 1ml of water.)  So 1g of solute in a water solution that totals 100ml means that the solute comprises very close to 1% of the solution by weight (w/w).  MrRedact 20:15, 12 November 2007 (UTC)
 * Both suggestions are perfectly logical explanations. Thanks. Rockpock  e  t  23:52, 12 November 2007 (UTC)

Running cool water over frozen drink defrosts. Why?
Sometimes I put canned soft drinks in the freezer, but I occasionally forget about them. When I finally take them out, they're frozen solid. I found out that I can run cool water (regular temperature) from the kitchen sink over the cans, while holding them at a 45 degree angle and rotating. After a few seconds, they're completely thawed out. If I take too long, they might even be too warm to drink! How does cool running water thaw out a frozen drink in only seconds? Steohawk


 * The drink you remove from the freezer isn't actually frozen solid — not even close. In fact, the ice that forms is neither contiguous nor very dense, because the sugar and carbonation bubbles in the soda pop interfere with the water molecules forming a contiguous lattice. It feels as though it's frozen solid because it only takes a fairly large chunk of fairly firm slush to provide enough support for the metal can to make it feel solid. Furthermore, water that feels "cool" (or "room temperature") relative to our normal body temperature actually contains a great deal of heat. Figure the soft drink is at 32°F. If you measure the "regular temperature" water coming from your tap, you'll probably find it is between 60°F and 70°F, for a ∂T of roughly 30 to 40 Fahrenheit degrees. The metal drink tin conducts heat very efficiently and uniformly to the contents, so your not-really-very-frozen drink "thaws" in a hurry.


 * Also, please sign your talk page and reference desk posts properly, not by manually typing in your user name, but rather by ending your post with four tildes ~ ~ ~ ~ (but without the spaces between them). --Scheinwerfermann 20:45, 12 November 2007 (UTC)


 * The water is cool - but it's above freezing - hence it's warmer than the ice and can melt it. I doubt your drink was frozen solid anyway because the pressure from the liquid expansion would likely split the can.  Since the freezer will tend to freeze the liquid towards the outside of the can before the inside, there may not be all that much ice to melt and it's right at the surface where the warmer (but still cool) tap water can melt it most easily.  I don't see anything weird going on here. SteveBaker 20:46, 12 November 2007 (UTC)


 * (edit conflict - GMTA) Who knows? Are we talking about soda (pop) like Coke? A few guesses: The can isn't really frozen solid, it just has a coat of ice all over the inner surface that makes it feel solid. When the water in the drink starts to freeze, it will freeze from the outside in because the heat is being lost through the can, and from the bottom up because of convection. As ice forms, the remaining solution will get more and more concentrated, depressing its freezing point more and more and helping it stay liquid. Running water is terrific at transferring heat, and if it's at all warmer than the can it will transfer heat to it. Do this: next time, take one of your cans outside and saw it in half with a big serrated knife (or get your mom or dad to do it). See if it is really frozen solid. --Milkbreath 20:58, 12 November 2007 (UTC)


 * Make sure to set up a video camera on a tripod and post the video to YouTube when you're done. It could easily be right up there with Diet Coke and Mentos!  :-)  SteveBaker 21:38, 12 November 2007 (UTC)

Thanks for the answers.

BTW, I did sign my last entry with four tildes (no spaces), but it got "converted" when I saved the page. Let me try it again. Steohawk 22:08, 12 November 2007 (UTC)


 * Yup, that time your signature worked. I'll add that if you are eager to see inside an aluminum pop can, the easiest and safest way to remove the lid is to turn an ordinary can opener (preferably a gear-drive Swing-a-way type) 90° so its wheels are horizontal rather than vertical, clamp the rim of the pop can between the cutter wheels, and turn the can opener's handle to remove the lid and part of the rim. Be careful, for this will create a sharp edge. However, it will not create metallic dust or other contaminants (as the hacksaw method would), so you won't spoil the contents of the can. --Scheinwerfermann 23:02, 12 November 2007 (UTC)

Melted ice contains white particles, even purified water.
Whenever I freeze water and melt it, white particles can be seen floating around in the water. They're never visible prior to freezing. I thought that this might have been caused by some impurity in the water from my faucet, so I froze water from my neighbor's purifier. After melting it, the same white particles were visible. They're even visible in hot water, so I know that they aren't tiny bits of left-over ice. What are these particles and why do they only show up after melting ice? Steohawk 22:14, 12 November 2007 (UTC)
 * Make sure that the container in which you make your ice is clean and not shedding dust or other bits of material and that you cover it with something similarly clean when you're freezing/melting it. Maybe put the water in a zipper bag during the freeze and thaw? My older plastic ice-cube trays used to flake off over time, and also the paint and other coatings in the freezer itself did. DMacks 22:29, 12 November 2007 (UTC)

Possibilities. 1. Your neighbour’s purifier is full of gunk 2. Your freezer is full of gunk 3. The container you are using is full of gunk 4. The back of your retinas are full of gunk. Myles325a 22:30, 12 November 2007 (UTC)


 * Is it possible that you live in a 'hard water' area? I could maybe imagine there being a lot of dissolved minerals in the water that could maybe come out of solution when you freeze the water - making these little particles.  What we need here is an experiment. (Woohoo! Actual science on the science desk!) The way to prove whether I'm right is to filter the water you get by melting the ice cubes and then re-freeze it in the same freezer/ice-tray that you used the first time.  If you melt it again and it has particles in it the second time around then the bits must have come from the freezer/ice-tray.  If there are no particles the second time around then DMacks & Myles are wrong and I guessed right.  As an alternative experiment, you could try washing your hands with a little soap and the melt-water (wait for it to get to room temperature first) and see if you get lots more lather than you do with tap-water.  Soft water produces more bubbles from soap than hard water and if I'm right and you somehow removed minerals by freezing and filtering - then you'd expect to get more lather with the melt-water.  SteveBaker 23:57, 12 November 2007 (UTC)


 * You might enjoy our zone refining article.


 * Atlant 17:50, 13 November 2007 (UTC)

E = mc2 - how does c relate to the weight and energy units?
Everyone can see why there is so much energy in a given mass, because c, the speed of light is so large, and c2 is enormous. But why couldn’t we just define c as a single unit? How does Einstein define a measure of speed with weights and energy values?

After all, c = sqr(E/m). I have often thought about this, tho obviously I am a layperson in physics, and my brain hurts. Myles325a 22:25, 12 November 2007 (UTC)


 * We actually have a page about the E=mc2 formula, with some info. One hand-waving reason that "c2 is more reasonable than c" here is that we need the units of measurement (dimensional analysis) to fit. A conversion factor for an energy/mass equivalence must be expressed in terms of distance2/time2). Once you have the relationship though, you can do algebra and other manipulations to express t he equation in different forms. Saying "c = sqr(E/m)" is not ideal because it fails if m=0. DMacks 22:37, 12 November 2007 (UTC)


 * In SI units, mass is in kg, lightspeed is in meters per second and energy is in Joules - which is SI shorthand for: "kilogram meters-squared per second per second" ...which is a bit of a mouthful.


 * You can work in any scale units you like so long as you are consistent. If you want to define your unit of length as (say) the distance light travels in a second (a "lightsecond") instead of the more usual 'meter' that's OK.  The E=mc2 equation still works - except that now we've defined c to be 1.0, instead of the result 'E' being in Joules (which is shorthand for kg.m2.s-2) the answer would be in some new unit of energy because we defined our unit of length to be a lightsecond instead of the meter.  Let's name it after it's creator and call it the 'Myle'.  The Myle is shorthand for kg.lightsecond2.s-2.  One kilogram of matter would contain exactly one Myle of energy...very convenient!  But the Myle would be a truly phenomenal amount of energy because it's in units that contain lightseconds2!!  The Myle simply isn't a very useful energy unit. A 'AA' battery stores about one kJ - but and inconvenient 0.09 attoMyles!  On the other hand, you could instead define your time unit as the time light takes to travel in one meter - c is still equal to 1.0 but your unit of time is microscopic - so your unit of energy is still enormous.  You can shuffle the unit definitions around however you like - but the result is the same.  Dimensional analysis is always very instructive in these cases. SteveBaker 23:31, 12 November 2007 (UTC)
 * It's also worth noting that when working with problems in relativity, velocities are generally expressed as fractions of c rather than using more common measurements. Donald Hosek 02:00, 13 November 2007 (UTC)

You might want to read up on Maxwell's equations. That's where Einstein got almost all of the theoretical support for the conclusion that E=mcc. --M @ r ē ino 14:27, 14 November 2007 (UTC)