Wikipedia:Reference desk/Archives/Science/2007 July 2

= July 2 =

Red light.
I'm doing a research project on Chambered Nautilus and in my local aquarium they nautilus are stored in a tank with dim red lighting. I know Nautilus are known for living in very deep and dark waters. Also, I heard somewhere that in very dark areas the first color to disappear is red light. Would this be a reason why they chose this color? --Agester 00:47, 2 July 2007 (UTC)


 * You're right in saying red is the first colour to disappear from shadowed areas. This is because it diffracts less than blue, which is better at illuminating areas not in direct light. In the sea, shadowed areas are not the issue, but absorption of light by water as it passes through. In this case, the opposite happens, and blue light is the first to be absorbd, so underwater environments are in fact much redder. Light in the aquarium doesn't pass through as much water as in these habitats, so I'm guessing the red lighting is a way to make the nautilus feel at home. Bendž|Ť 10:48, 2 July 2007 (UTC)


 * Your statement that blue light is absorbed more than red in water is very counterintuitive, and these references say blue is least absorbed . Do you have any references that it's redder in the briny deeps?  Perhaps due to scattering, as in a sunset?  Thanks!  --TotoBaggins 21:02, 2 July 2007 (UTC)


 * Since red light is almost nonexistant at the depths involved, I wouldn't be surprised if the nautilus is unable to see it. In that case, the red light is both a way of keeping the nautilus dark enough for comfort, but lighting it enough for people to see. --Carnildo 22:01, 2 July 2007 (UTC)


 * Red light is also good if you want a dim light that will keep people's eyes dark-adjusted. I've seen it used (I think) in situations such as lighting the sound mixing board in an otherwise dark auditorium.  So one reason for using it in a public aquarium might be to give just enough light for the human visitors to see by so they don't run in to each other, but keep their eyes adjusted so they can see the weird deep-water fish in the almost-dark tanks. --Steve Summit (talk) 23:12, 2 July 2007 (UTC)

skin -kojic acid;azelaic acid;bearberry, mullbery, vitamin c
a cream or exfoliant containing the ingredients in the heading are suppossed to improve and brighten the appeareance of the skin... are they dangerous or harmful at all?

can you tell me of any over the counter product of a respectable brand that contains the former compounds?

thank u.


 * You could read our articles on kojic acid, azelaic acid, bearberry, mulberry and vitamin C. The berries are edible, so those are presumably safe.  As for the exfoliant as a whole, it is generally safe to presume that anything sold in at pharmacies in the United States is safe to use, and likely underwent animal testing.  Barring any allergies, and of course obeying the manufacturer's suggested amount and frequency of use.  I don't know of any in particular that have these chemicals, but like i said before, if you see it in a pharmacy, do what the bottle says and you probably won't have problems.  Ask your dermatologist if you're worried.  Don't buy chemicals over the internet...  Someguy1221 04:14, 2 July 2007 (UTC)


 * If it is marketed as an herbal supplement it might not have been tested; the FDA does not regulate herbal supplements with any regularity (it treats them as food, not as drugs). --24.147.86.187 12:47, 2 July 2007 (UTC)

Heat Shield
I read an article once in Popular science about sending payloads into space with a magnetic launcher, mass driver. I was wondering though how much shielding would be needed for traveling through the air at escape velocity? 


 * Why would this be any different from any other spacecraft? See especially the 'Thermal control' section in spacecraft subsystems. While a magnetic launcher may mean the spacecraft doesn't need to be able to handle the heat produced in a fuel based launch, it doesn't alter it's requirements for withstanding the heat produced by passing through the atmosphere. See also atmospheric reentry. --jjron 03:17, 2 July 2007 (UTC)


 * There is a difference between the two situations. On re-entry a spacecraft is deliberately trying to slow down by dissipating its kinetic energy as heat energy, so it is trying to generate as much drag as possible. In the launch situation, however, you want to minimise energy loss, so you want low drag, with a streamlined profile. Contrary to intuition, a streamlined profile actually requires more heat shielding than a blunt profile - see Blunt Body Theory. However, this difference is probably immaterial - because escape velocity is over 20 times the speed of sound at sea-level, a spacecraft launched by a mass driver, with no on-board engines, would have to travel at hypersonic speeds at launch. Because of this, I doubt that an Earth-based mass driver is a practical launch mechanism unless the payload travels in a vacuum - in a space fountain for example. Gandalf61 09:19, 2 July 2007 (UTC)


 * There's a *huge* difference between the two situations: a chemical rocket is at its slowest near the ground where the atmosphere is at its densest, and picks up speed as it goes; a launcher-fired projectile is at its fastest near the ground, and loses speed as it goes. --TotoBaggins 20:06, 2 July 2007 (UTC)


 * Bah! Passimists!  Yes you are going insanely fast through the densest air...not good!  But the temperature conduction through your heat shield isn't immediate - the mass-driver vehicle isn't in the dense atmosphere for very long.  Crunch the numbers guys/gals (sorry, I'm in a hurry - these numbers are from memory): At launch your projectile is heading out at maybe 12km/second - that's escape velocity. The troposphere (~75% of the mass of the atmosphere) lies below ~20km altitude at the equator...and below ~10km at the poles.  So bury your mass driver in the ice at the South pole and shoot your projectile vertically up at escape velocity.  It'll be subject to atmospheric heating for rather less than a second!! So you need an insulator that conducts heat just slowly enough to protect the skin of your craft for just ONE second!  Remember...Thermal conductivity is heat transferred though some area in some amount of time.  We don't need a really low conductivity if the time is short enough...and it is.  Then you may discarded the heat shield before the heat on it's surface is conducted through to the payload.  It's short - violent - but possible.  The real problem with mass drivers is finding some interesting payloads that don't mind a few tens of g's of accelleration during launch! SteveBaker 00:36, 3 July 2007 (UTC)


 * I don't think heat shielding is the biggest obstacle here. Problem 1 - launch acceleration. Let's assume the launch tunnel is as deep as the Kola Superdeep Borehole - thats 12km. To reach a terminal speed of 12 km/s over a distance of 12km requires an average acceleration of 6 km/s2 - that's about 600 g. Problem 2 - drag. A bullet fired horizontally loses one third of its muzzle velocity over the first 500m of its range (see External ballistics) - and that's at supersonic speeds, not hypersonic. Even assuming drag is no worse at hypersonic speeds, you will need a terminal velocity (on leaving the launch tunnel) many times higher than escape velocity. This then compounds the launch acceleration problem, as average launch acceleration is proportional to the square of the terminal velocity. As a certain Chief Engineer once said "A canna' change the laws of physics". Gandalf61 10:47, 3 July 2007 (UTC)


 * Absolutely - I agree entirely. However, the questioner was asking about the heat shield - not about the overall practicality of these gizmos.  You're absolutely correct in saying that the ballistic drag on the payload would be phenomenal - so the muzzle velocity would have to be much more than 12km/s.  However, that only serves to further reduce the amount of time the object is within the atmosphere.  These 'mass drivers' might be useful for things like launching large chunks of ice to a colony on the moon - or lumps of metal ores to orbital refineries turning out space station components.  Bulk materials that won't suffer from 600g accellerations - and which need to be launched cheaply and at high payload capacities without generating too much air pollution from rocket exhausts and such.   It's still not obvious that it can be done - but I maintain that the reason it's tough has nothing to do with heat shielding.  Ice makes a pretty good insulator - if we were shooting thousands of tons of water to a lunar colony - we probably wouldn't bother with shielding at all.  Just cast the water into the right shape - use a metal sabot to get the thing accellerating and even if half of the ice melted and boiled away on the way up (which I doubt it would), you're still onto a winner. SteveBaker 12:21, 3 July 2007 (UTC)


 * Won't 600 g's cause massive heating throughout the slug, not just at the surface ? StuRat 02:54, 11 July 2007 (UTC)

WOOT cool thanks for the answers.68.120.85.164 05:26, 4 July 2007 (UTC)

Are all Neoptera holometabolic?
Are there any Neoptera outside Endopterygota? If you know the answer, it may be helpful to include it in those articles. If it is already there and I somehow missed it, I apologise for wasting your time. Wikipeditor 02:34, 2 July 2007 (UTC)


 * Sorry, but doesn't the taxobox at Neoptera answer this question? It seems to list the superorder Exopterygota and 11 other orders outside Endopterygota. --mglg(talk) 02:45, 2 July 2007 (UTC)


 * According to our articles Neoptera is an infraclass, Endopterygota is a superorder within that infraclass, therefore indicating that all Endopterygota are Neoptera. --jjron 03:03, 2 July 2007 (UTC)


 * My question was whether it is the other way round, but thanks nevertheless. Wikipeditor 03:11, 2 July 2007 (UTC)


 * D'oh! It seems I had only checked the German article on Neoptera and somehow misunderstood all Neoptera to belong either to Endopterigota = Holometabola or to a paraphylic group of Exopterigota.
 * The English article is much clearer. Thank you! Wikipeditor 03:11, 2 July 2007 (UTC)


 * Sorry, I had misread your question, but my answer stands. You are correct, the articles could perhaps be clearer on this. However, what you say in your 'doh' still doesn't sound right - there's the Superorders Endopterygota and Exopterygota, plus eleven other orders outside these two superorders within the Neoptera. --jjron 03:32, 2 July 2007 (UTC)

Development of the water tank
Hello Wikipedia, I am looking for some rather specific information which I have had some difficulty in finding. I am looking for dates of significant technological developments of the water tank (specifically, the backyard rainwater tank) which would help me put together a good picture of it's history. I have information like the dates of introduction of technologies like hot dip galvanization (helped produce a metal tank which was less susceptible to corrosion) and the dates of development of technologies that facilitated industrial polyethylene and fiberglass production which are also used extensively in tanks. Any information or assistance would be greatly appreciated. Dates of milestones, breakthroughs and innovations is what I am aiming to find out.

Thank you, --Waynekruse 02:55, 2 July 2007 (UTC)
 * Whatever you find vis a vis the history of galvanized or plastic tanks, be aware that in the 19th and early 20th century (if not earlier) it was common to have a rainbarrel of wood sited to catch runoff from the roof, which women could use to wash their hair. Since it had no minerals in it like well water, simple laundry soap worked better with the soft rain water. Cisterns served much the same function plus serving as a well substitute. Edison 03:12, 2 July 2007 (UTC)

Name of Flower
Can someone help me identify a particular flower? I used to know the name, have been searching through my books, but some of my books are missing. I've also tried searching the "net" but haven't had much success yet. The flower is roughly 12" tall. It has green leaves that are somewhat pinnate and which are not smooth to the touch.  It has clusters of purple/violet colored flowers at different sections of the main stem.  The stem is somewhat squarish--as if it might be in the mint family.  The flowers individually are perhaps the size of a nicket (+ or -), but are bunched together around the stem at various intervals. Thanks so much if you cfan identify it or set me in the right direction.  My mind wants to think the name began with a "v", but I cannot find any flowers that start thus and look like the plant I am describing.  I might be able to upload a picture is someone needs it. . . . Thanks for any help!  Rfhallock 05:55, 2 July 2007 (UTC) Email removed to minimize spam


 * Have you looked at Hyacinth (flower), Grape hyacinth, crocus, iris (plant), and violet (plant)? Nimur 07:07, 2 July 2007 (UTC)


 * What's a nicket? One really has to know more about the flower itself. How many petals? Symmetry? Ovary superior or inferior? Though it all points to the lamiaceae, apart from the pinnate leaves. Could be in fabaceae. Many vetches have purple flowers Bendž|Ť 10:59, 2 July 2007 (UTC)


 * Bracted Vervain perhaps? --TotoBaggins 20:37, 2 July 2007 (UTC)

Sounds like a form of Polemonium. Hardyplants 22:24, 2 July 2007 (UTC)


 * How about Veronica? --Eriastrum 19:14, 3 July 2007 (UTC)

Moisture transmissivity of Aluminium.
Hey all, I've found some papers that discus the water transmissivity for an Al film of given thickness. I'm wondering if you would expect the ingression rate to be proportional to the thickness of the coating? I can't find any solid data on this. I have some data for other plasticy materials which suggest a linear relationship. Would this be the same for metals? 213.48.15.234 09:35, 2 July 2007 (UTC)


 * At diffusion equilibrium, the rate of transmission through a barrier is approximately proportional to its thickness. The time required for the equilibrium rate to be established is roughly proportional to the square of the thickness, so roughly speaking a barrier twice as thick prevents noticable seepage for 4 times as long.  Dragons flight 10:30, 2 July 2007 (UTC)


 * Thanks, great answer. Can you find any sources? I've been looking all morning. 213.48.15.234 10:37, 2 July 2007 (UTC)
 * I was thinking that for a thin film of aluminium it would be linear, as grain boundaries might be present through the whole thickness. But as you get to thicker films (thicker than the grainsize) it would become non-linear, as there is no longer a single grain boundary. Any thoughts? 213.48.15.234 14:12, 2 July 2007 (UTC)

Future of Technology Ten Years From Now
Can someone list approx 10 technological advances would affect us (in everyday life) ten years from now? whether it is medicine, entertainment, etc. —Preceding unsigned comment added by Juliet5935 (talk • contribs)

Um..10? I'll list as many as I can think of, the others can come up with better ones..
 * 1) Credit cash (literally credit cards, no cash)
 * 2) Virtual machines that shows you a vacation spot you like. Use it in the office to get some stress off. Size like normal sunglasses.
 * 3) There's an "Aroma Jockey" in Amsterdam, which couples music, sight, and smell together.
 * 4) Bloomframe, a very sassy window and balcony. Push a button, it pops out like a shelf into a balcony; push a button, it pulls back into a big window.

That helps? Cheers!!! (Most information adapted from Reader's Digest) - Zachary crimsonwolf  14:02, 2 July 2007 (UTC)


 * Sorry if I'm being overly-suspicious, but this sounds exactly like the sort of thing that is asked as homework, to try to make a student think. I cannot think of a reason someone would want this sort of list if it wasn't homework. If you look for a ready written list, or ask other people to do it for you, you get none of the benefit and miss the point. There won't be a right or wrong answer for this homework, and it's probably meant to be fun, so just think! Skittle 15:58, 2 July 2007 (UTC)


 * I suspect homework as well. Here's a competition to build a flying car.  Nimur 16:26, 2 July 2007 (UTC)

You are correct, SKITTLE and NIMUR, in that you are being overly-suspicious. I am a 35 year old woman who had an innocent request for other people's opinions. What I am overly-suspicious of is that it appears a LOT of the answers to all of the questions in the Wikipedia Reference Desk contain the following phrases: "Do your homework!" "I am not going to answer that as it appears to be a honework question", etc. If that is the response that people are going to get when they ask a question, then why bother having this Reference Desk anyway?!

......oh and by the way, Crimsonwolf, thank you very much for contributing!

Skittle, skedaddle with your stumbling block! Nimur, no more of your nuisance! —Preceding unsigned comment added by 209.0.0.29 (talk • contribs)


 * Some editors might like to try assuming good faith and even being nice to newbies. DuncanHill 19:48, 2 July 2007 (UTC)


 * "Prediction is hard, expecially the future." Ten years is a very long time in today's world. Some people think that change will be so fast in the next decade that the world will be unrecognizable. Please see Technological Singularity. Another interesting idea: look back at 1997. -Arch dude 21:18, 2 July 2007 (UTC)


 * Ten years ago feels like the extended present. I do not see anything like the pace of technological progress there was in an equivalent ten year period 100 years earlier, considering progress then in aviation (the Wright Brothers) made the first powered flight, radio (Marconi claimed to have sent a transatlantic radio signal), the widespread exhibition of motion pictures and medicine (the X ray became useful). Genomics (published genomes, functions of genes) and astronomy (discovery of numerous exoplanets, evidence of water on Mars and the moon, Mars rovers) would be the most dramatic science/technology things in the last 10 years. Otherwise for the past decade I see creeping incremental progress. Smaller celphones, better DVDs, faster PCs. Big whoop. I hope things which make life better come along at a faster pace in the next ten years: cures for more diseases, robocars to reduce the 35,000 vehicular deaths a year in the US, better batteries to make electric cars practical, and maybe something which helps world peace fall into place before nuclear proliferation adds nukes to the terrorists' toolkit. Edison 22:09, 2 July 2007 (UTC)


 * Nevertheless the reference desk is NOT a soap box: It's not for asking people's opinions and having a discussion about it. --antilivedT 22:21, 2 July 2007 (UTC)


 * In just 10 years...tricky. We can't go with nanotechnological assemblers or space elevators or human minds transferred into software - those are 40 or 50 years away.  Over ten years, it's reasonably safe to predict that no really radical technology will come along AND make it into mainstream life.  All of the things we marvel at right now are technologies that were basically around 10 years ago - but not as cheap/fast/small or whatever.  We can shoot for some easy ones: I guess we'll have computers that are about 100 times faster (if Moore's law doesn't crap out on us first) - and it should be possible to store every book and every piece of music in existance on your 2017 model iPod with room left over for every movie you own...but without some radical changes in the way copyright law works - it's really not going to help you much.  I'll be seriously upset if we don't have a majority of cars and light trucks doing 60+ mpg in 2017.  Perhaps the RepRap project will really take off - that could make a MASSIVE difference to our lives - being able to make a huge range of plastic and metal objects in a box the size of a refrigerator from plans you can download for free from the Internet and using easily recyclable materials.  That would be fairly earth-shattering.  (Hint: Don't hold on to shares in WalMart if this happens!).  As other have said - look back at what has changed since 1997.  Not a whole lot actually.  We have things like MP3 players and tiny, ubiquitous telephones.  We have digital cameras.  But all of those things were around in 1997 - they were just big clunky things that cost a lot of money and didn't perform all that well.  2007's versions of those things aren't materially different - it's just that we can all have them if we want - and they are immensely capable.  We had the Nintendo 64 game console in 1996 - and now we have the PS-3 - but the games are rather similar, a bit nicer looking - more realistic - but not radically different.  We had DVD's in 1997 - and in 2007 we're just starting to switch to Blu-Ray...which is a little better - but not earth-shattering.  Stuff like HD television has been around since the 1980's - but only now is it getting some serious market share.  It's really too late to start thinking about putting men on Mars by 2017.  Nope - my prediction is more of the same - smaller, cheaper, faster, more energy efficient...but nothing really dramatic.  Go on - I'll give you a free replay - ask again, but for 50 to 100 years! SteveBaker 00:15, 3 July 2007 (UTC)


 * Phrasing your question in that case to make it sound like homework (IMO) when you could have made it more conversational / discussion sounding isn't then really the best idea :) 194.168.231.2 11:18, 3 July 2007 (UTC)Wes

Maybe I have been out of school for some time, but why must we "re-phrase" questions anyway. The question I posted is exactly how I wanted it phrased. I do not have to change the way I ask questions for anybody. It is ridiculous that we cannot answer the question at hand without defending the validity of the actual question. Focus on finding the answer to the question itself instead of where it has originiated from!


 * But thing is, if someone was trying to cheaply use the Reference Desk as a homework service, then he would not gain anything, and it would be contrary to our objective. We're not trying to attack you, just that, as in real life, the way you express a question can be interpreted in different ways. Splintercellguy 19:09, 3 July 2007 (UTC)


 * I apologise for those who are creating this fuss - they clearly haven't read the helpdesk guidelines properly (WP:AGF and perhaps also WP:BITE would be good starting points!). Assuming Good Faith means not accusing someone of asking a homework question unless you have solid evidence.  In the absence of strong evidence, one must assume good faith on the part of our questioners.  Sadly, we really can't control who answers questions.  You don't need to rephrase anything - your question was perfectly valid.  What triggered this was probably the specificity with which you asked for TEN things - this is suggestive of someone who just typed in the question at the top of their homework assignment and hoped we'd do it for them.  Most people who were merely curious would probably have asked for "some" predictions of the future.  However, one must assume good faith on the part of questioners - and for all we know you are writing a "Top 10" piece for a newspaper - or perhaps you are even setting homework for some kids and wanting some interesting answers of your own to give.  This is what it means to assume good faith.  Like I said - please try to ignore the hot-heads. SteveBaker 19:15, 3 July 2007 (UTC)


 * With all due respect, I did provide a civil and useful response, even though I questioned the motives of the original poster. As with other instances when I suspected homework, I merely identified my suspicion, and provided a "reference" instead of a "solution."  I think this is the best course of action for the reference desk.  If anybody feels that they have been sleighted, I apologize; but I don't think my responses have been disrespectful.  Nimur 03:13, 4 July 2007 (UTC)

Oh, everyone, just know that no one is wrong. The questioner (I shall call him/her Annonymous for now) came here to ask for an answer; Nimur and Skittle just wanted him/her to be creative and try to find an answer him/herself. No grudges! Cheers!!! - Zachary crimsonwolf  14:14, 8 July 2007 (UTC)


 * Here are some changes possible on cars:


 * 1) Use of cameras to supplement, or in place of, side-view and rear-view mirrors.


 * 2) More hybrids and more electric cars.


 * 3) More use of regenerative breaking.


 * 4) Widespread GPS technology.


 * 5) Internet access from cars, integrated with software, say to find the cheapest gas available at the next highway stop.


 * 6) More use of all-wheel drive, speed sensitive steering, adjustable suspension systems, etc.


 * 7) More use of heads-up displays.


 * StuRat 02:45, 11 July 2007 (UTC)

Re:Lava lamps and chemical lights
What exactly are lava lamps made of? And chemical lamps? - Zachary crimsonwolf  13:45, 2 July 2007 (UTC)


 * Did you look at the article on lava lamps? I found this on Light Sticks which is probably what you're looking for. Donald Hosek 21:50, 2 July 2007 (UTC)


 * Our article on Glowsticks has a good diagram showing how all the reactions work. Laïka  10:31, 3 July 2007 (UTC)


 * I'm glad to see that the article at Lava lamp is back again. It was gone there for a while.  Corvus cornix 16:12, 3 July 2007 (UTC)


 * Yeah. I tried the article, but all there is was a "this page is protected" template and nothing else. Blank. Anyway, thanks to you!!! Cheers!!!! - Zachary crimsonwolf  14:01, 8 July 2007 (UTC)

A list of Hispanic scientists?
Hi. I need to find a list of Hispanic scientists (past and present) and their achievements. Thanks. Xiner (talk) 14:19, 2 July 2007 (UTC)


 * Did you see List of notable Hispanics from the United States? I can't find anything else right now. 213.48.15.234 14:25, 2 July 2007 (UTC)


 * Category:Spanish scientists might help Algebraist 18:26, 2 July 2007 (UTC)

Membrane potential
hi i want to know is there difference in voltage between epiderm and hypoderm? —Preceding unsigned comment added by 221.223.44.101 (talk • contribs)
 * Voltage in epidermis and hypoderm? I don't think those things carry appreciable amounts of "voltage", if you connected a copper wire between your epidermis and your hypoderm I can't see how it could generate any current flow. Vespine 22:52, 2 July 2007 (UTC)

protein/protein interaction
What are prey and bait in protein/protein interactions?. could you please give me a link that explains the basics of log2ratio and how it is used for measuring the reactions?.


 * Perhaps a more detailed question would be easier to answer. Someguy1221 06:07, 3 July 2007 (UTC)


 * I'm guessing you may be referring to protein microarrays or yeast two hybrids, both methods for determining protein-protein interaction. In a yeast two hybrid, if you have protein X and you wish to know what other proteins bind to it, then protein X is referred to as the bait and whatever binds to it is the prey.
 * A log2 ratio as a way of representing a difference between the readout values in a baseline (control) and an experiment. A log2 ratio of 1 is the same as a fold change of 2. Rockpock  e  t  18:05, 4 July 2007 (UTC)

rigveda, translation bij Griffith
LS I'ld like to know if the translation bij Griffith : "Rigveda V1", edited by Kessinger, contains the full text. What does the V1 mean? [volume? there is no V2 etc]. Contact with Kessinger is hardly/not possible. Thanks, Ruud Lensen, the Netherlands 193.172.24.226 16:23, 2 July 2007 (UTC)

Help Needed
Is energy material? I couldn't find the direct answer to the question in the article. -PatPeter 17:17, 2 July 2007 (UTC)
 * No. Energy is "the ability to do work"; in other words, energy is a capability. It is a property of matter, like charge or mass. It is not itself material. Batmanand | Talk 19:18, 2 July 2007 (UTC)
 * Well, yes and no... This is the general view of classical physics. You may want to read about Mass–energy equivalence, if you are looking for more advanced materials. Michel M Verstraete 21:40, 2 July 2007 (UTC).
 * If a 5 ton truck acceleraates from 0 to 70 miles/hour, its mass increases an infinitessimal and unmeasurable but calculable amount due to the added kinetic energy. If a subatomic particle accelerates to an appreciable fraction of the speed of light in an atom smasher, its mass increases dramatically. Edison 22:16, 2 July 2007 (UTC)
 * Would it still have the same amount of matter? -PatPeter 18:39, 3 July 2007 (UTC)


 * Yes, it would still contain the same amount of "matter", in the sense that the number of atoms etc. would remain the same. When we say that it an object that has gained energy (by, say, being heated a few degrees) is "increasing in mass", we mean only that its inertia has increased (i.e. it has become harder to accelerate or decelerate the object) and that its gravitational mass has increased (it would register as having a very slightly larger mass, if weighed on a hypothetical, ideally sensitive scale). But the number of atoms, and the nature of each atom, is exactly unchanged. --mglg(talk) 03:53, 4 July 2007 (UTC)


 * The deal is that a very small amount of mass is equivelent to an enormous amount of energy (E=mc2 - and 'c' is a HUGE number!) - and in everyday experience, we don't see mass turning into energy because it takes reasonably extreme circumstances to make that happen (nuclear reactors and such). Conversely - the amount of energy that's out there in a 'normal' situation corresponds to an utterly microsopic amount of mass - so (as User:Edison points out) you don't notice that something like a truck that's moving fast (in human terms) is a teeny-tiny bit heavier.  So this mass/energy duality thing doesn't fit with our normal range of experience. SteveBaker 19:02, 3 July 2007 (UTC)

White teapot or black teapot
Has any experimental work been done to see in which sort of teapot the tea cools down more slowly? I would have thougt the white teapot if just considering radiation, but Im not sure. Any answers? —Preceding unsigned comment added by 88.110.40.127 (talk • contribs) 22:52, 2 July 2007


 * That's probably true, but I think the infrared emissivity would be more important than visible light at teapot temperatures. — Omegatron 22:57, 2 July 2007 (UTC)


 * I would also be interested in any data relating to metal vs. ceramic teapots too. (I am partial

to a cuppa). DuncanHill 23:00, 2 July 2007 (UTC)


 * Metal is a better conductor of heat than ceramic - so the metal teapot will cool much faster than the ceramic teapot. The colour of the teapot is a tricky matter - what it's made of is vastly more important - and you can't change the colour without changing what it's made of so it's not even really possible to compare purely the colour. SteveBaker 01:20, 3 July 2007 (UTC)


 * Well you CAN change the colour of ceramics without much affecting their other properties; and if you go for metal cans you have to paint it either black and white anyway, so it's just a painted can, differing in the colour of the paint. --antilivedT 09:29, 3 July 2007 (UTC)


 * You may want to choose a white cearmic teapot over a black ceramic. You'll notice that most water heaters are painted white. While a black object absorbs more light, it also emits heat as radiation more readily, the same process in reverse. Source: recent posting in the "last word" section of New scientist. (www.newscientist.com) EverGreg 10:34, 3 July 2007 (UTC)


 * Would a highly polished metal teapot radiate less heat than a metal teapot painted white? (Or should I just get a tea-cosy? DuncanHill 10:38, 3 July 2007 (UTC)


 * The answer by Omegtron seems to make sense. So its not the actual visible color, but what it looks like in the infra red. I seem to remember someone who had done some experiments with black and white painted metal strips in sunlight and measured the temperature difference. Surprisingly (?) he found very little differnce. I think he said it was because the emissivities of all paints was about the same.--88.110.40.127 11:21, 3 July 2007 (UTC)


 * How things look in Infrared is pretty counter-intuitive. I used to work in military flight simulation where my specialty was the accurate simulation of infrared cameras - so I have quite a bit of knowledge in this area.  A while back, I was looking at video from an IR camera - watching cars driving along a black tarmac road at night.  I was initially puzzled that the cars seemed to be casting shadows on the road...at night...!  It turned out that the camera was set up in 'black-is-hot/white-is-cold' mode (most military IR cameras can switch between 'positive' and 'negative' images) - so the dark patches that I was seeing were hot spots under the cars as they drove along - a kind of 'anti-shadow'.  It was clearly impossible for the road to heat up and cool down again fast enough to account for these short-lived hot-spots.  It turns out that tarmac - whilst being pretty black (ie non-reflective) in visible light - reflects IR pretty strongly.  What I was seeing was a reflection of the underside of the hot engine bay of the car in this mirror-like tarmac!  If there is one lesson I definitely learned from that and other similar findings, it's that it's very dangerous to make any assumptions about the properties of a material in IR versus visible light.  If this surprises you, think about this.  Something that appears to be bright red in visible light is strongly reflecting red light - yet strongly absorbing green light.  Red and green are much closer in frequency than (say) red and the medium-range infrared that's the cause of most heat loss.  However, even that is misleading - we're more interested in how IR energy is emitted by an object than we are about how much it reflects (which is what we mean when we talk about an objects' "colour").  The IR emissivity and visible spectrum reflectance of a surface are not really closely correlated.  So whilst you can do experiments with a particular pair of colours of the same object and perhaps get the same result for a particular material - that is very far from being proof that this is true for all materials that differ (seemingly) only in their colour.  Short answer: You don't know for sure just by looking at the colour without having a heck of a lot more information about the substance(s) involved. SteveBaker 12:09, 3 July 2007 (UTC)


 * Sorry I should have been clearer. What I meant by 'looks like' was how an object (at a known absoulute temperature with no external source of infra red shining on the object) would look to you if you had infra red vision. This I believe to be a measure of its emissivity. See Wein's Law, Stephan-Boltzmann law, Stephan's Law, (when thay are written) and Black body radiation--88.110.40.127 12:57, 3 July 2007 (UTC)
 * OK. The amount of IR light emitted depends on the 'emissivity' (which I guess you'd describe loosely as 'the ability to radiate') and the temperature.  So, yeah - if you have two objects with the same surface temperatures and you pointed an infrared camera at them then they will appear with different brightnesses in the camera if their emissivities are different.  An IR camera doesn't measure temperature directly because it's not measuring the frequency of the light - only the amount of it that's within it's range of sensitivity.  To measure temperature remotely, you need a Bolometer.  Hey!  I know a poem about bolometers.  "Sam Langley invented the Bolometer - which is really a kind of thermometer - that can measure the heat - from a polar bears feet - at a distance of half a kilometer." - Feel free to applaud at any time.  Any time at all.  Now would be good. SteveBaker 16:16, 3 July 2007 (UTC)

Tea cosies
There is an article on tea cosy but it doesnt say how they work. They certianly keep your head warm if you pull them right over your face (as I remember from childhood), but from the above comments it seems that they would not block the IR from your head. My assumption is that they prevent conduction to the air and cooling convetion currents. Maybe some one could find a ref and add to the tea cosy article.--88.110.40.127 13:22, 3 July 2007 (UTC)
 * Exactly, they work like clothes. They keep a layer of air trapped which warms up and cannot escape. This prevents convection, and reduces conduction. 213.48.15.234 14:13, 3 July 2007 (UTC)