Wikipedia:Reference desk/Archives/Science/2009 May 12

Science desk
< May 11	<< Apr | May | Jun >>	May 13 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

May 12

cold virus and cold water

we all know that common cold is caused by a virus. Then why do people say that drinking chilled water that is purified earlier will cause cold?--harish (talk) 01:18, 12 May 2009 (UTC)

1. We don't all know this.
2. We don't always act rationally on what we know

Old wives' tales and folk remedies (or folk ailments) are unlikely to be spontaneously extinguished in a fit of rationality. — Lomn 01:35, 12 May 2009 (UTC)

There is a quality of free association that one finds with pre-bacteriological understandings of disease. "Hmm, mild sicknesses appear to increase in the winter -> must be because of the cold -> other things that are cold must cause illness." --98.217.14.211 (talk) 01:53, 12 May 2009 (UTC)

"List_of_common_misconceptions#Health". Axl ¤ [Talk] 16:38, 13 May 2009 (UTC)

using computer and eye problems

The computer monitor is just like any other object in the environment. If we reduce the monitor brightness and use an anti-glare screen, the monitor will have the same brightness as other objects. We don't get eye problems if we gaze at a table for long hours. But if we do the same for a computer, why do we get eye problems?--harish (talk) 01:22, 12 May 2009 (UTC)

Gazing at anything for long hours may inhibit blinking which may lead to dry eyes and all the common related problems. What specific "eye problems" are you referring to? -- kainaw™ 01:38, 12 May 2009 (UTC)

You can get eye strain reading a book for too many hours in a row too. Holding something in front of your face and staring at it intimately for hours and hours is generally not great on the eyes. The problem with computers is that the time flies by pretty dang fast. I don't think it is a problem with brightness per se. --98.217.14.211 (talk) 02:57, 12 May 2009 (UTC)

By eye problems, i mean myopia or something like that. People warn that using the computer for long hours will result in wearing spectacles--harish (talk) 05:00, 12 May 2009 (UTC)

People say all sorts of things. Perhaps you should ask them for the evidence.--86.25.193.179 (talk) 05:51, 12 May 2009 (UTC)

And yet many people who do not use the computer for long hours also end up having to get spectacles... while many people who use computers every day don't. I don't think it's as simple as "don't look at X too much". -- Captain Disdain (talk) 08:26, 12 May 2009 (UTC)

You can definitely get eye-strain from staring at a monitor for too long - but that's a temporary condition, the muscles are simply getting tired from holding the same (short) focal length for hours at a time. You rest - they get better. Taking some time out every 10 minutes or so to stare out the window - or somewhere else as far away as possible - definitely helps. But I've been using computer screens in my job and at home ever since there WERE computer screens - and although I'm a little short-sighted, I can still pass the eyesight test for my driver's license without glasses. I don't think we have solid scientific evidence on this, either way, but it's certainly not as black and white as some people make out. SteveBaker (talk) 12:02, 12 May 2009 (UTC)

(anecdotal evidence) I've been using computers since I can remember (2-3 years old) and for LONG hours a day. That includes long hours with those old monitors with very low refresh rates, high radiation and so. Also, I've been reading compulsively both in the computer screen and in paper with poor illumination. Needless to say, I've been repeatedly told that I would damage my eyesight. Now I'm 23 and my eyesight is perfect. Even glasses with very slight correction are incredibly uncomfortable for me. Only when I was very young I remember that sometimes my eyes itched after playing with my old MSX for too long, but, for some reason, it happened like 3-4 times and never happened again. --Taraborn (talk) 13:33, 12 May 2009 (UTC)

Temperature of the Exosphere

A line in the recent Scientific American (sorry, I know, I'm just bored, and the website is so flashy...) states <anofollow" class="external free">http://www.scientificamerican.com/article.cfm?id=how-planets-lose-their-atmospheres&page=2">thus</a>:

The temperature at Earth’s exobase oscillates but is typically about 1,000 kelvins, implying that hydrogen atoms have an average speed of five kilometers per second. That is less than Earth’s escape velocity at that altitude, 10.8 kilometers per second, but the average conceals a wide range, so some hydrogen atoms still manage to break free of our planet’s gravity.

1,000K at the exobase? Isn't that a little bit high? Is this a typo or am I missing something? 219.102.221.127 (talk) 03:40, 12 May 2009 (UTC)

May be this previous discussion gives some hint about the temperature issue. manya (talk) 04:26, 12 May 2009 (UTC)

See thermosphere. Looie496 (talk) 04:29, 12 May 2009 (UTC)

Ah, I see thank you. Darn, I missed it by one sphere. Maybe it should be added to the exosphere article that the temperature in parts can be extremely high, or at least that the fast moving particles of the exosphere have very high energies. 219.102.221.127 (talk) 05:26, 12 May 2009 (UTC)

dogs and grass

Why do dogs eat grass? Mine seems especially hungry for it in the spring. --Halcatalyst (talk) 04:01, 12 May 2009 (UTC)

Let me google that for you. :) manya (talk) 04:19, 12 May 2009 (UTC)

Many dogs are idiots. Tempshill (talk) 04:38, 12 May 2009 (UTC)

Many animals eat stuff not naturally considered part of their diet. Parrots eat clay, chicken eat pebbles, cats eat grass, birds eat various herbs. Some of these things have been found to help digestion or serve medical purposes. 71.236.24.129 (talk) 08:21, 12 May 2009 (UTC)

Interestingly enough, I used to have a pet duck that used to eat it's own feces after it had dried.--KageTora (영호 (影虎)) (talk) 01:05, 13 May 2009 (UTC)

<pedantry>'they'. the singular is fex.</pedantry> —Tamfang (talk) 06:01, 14 May 2009 (UTC)

Dogs, if they were still running in packs and actively hunting like wolves, would normally get fiber and veg proteins etc. by eating the intestinal tract of thier prey (partially digested grass and other stuff). I would suspect they eat grass to supplement this now missing fiber/vitamin source.67.193.179.241 (talk) 12:16, 12 May 2009 (UTC) Rana sylvatica

My vet said some dogs eat grass if they have indigestion; or Grassiscon. Or they may just like the taste of it. Lanfear's Bane | t 12:44, 12 May 2009 (UTC)

Cats often eat grass just before they are sick (presumably for a problem with digestion). Is there some scientific explanation? Would it work for human indigestion? (I prefer mints) Dbfirs 08:21, 13 May 2009 (UTC)

Many pet stores sell little pots of wheat or oat grass for cats to eat. (Our cats love the stuff!) So, I doubt that the stores are selling it with the intention that the cats throw up on their owners carpets, counter-tops, etc. Dismas|^(talk) 10:01, 13 May 2009 (UTC)

Trouble can ensue if they don't throw up their hairballs. —Tamfang (talk) 06:01, 14 May 2009 (UTC)

• Thanks all for your responses. --Halcatalyst (talk) 15:53, 14 May 2009 (UTC)

Many dogs and cats will eat grass on a regular basis. Feral cats eat grass daily. ~AH1^(TCU) 16:42, 18 May 2009 (UTC)

Is the speed of everyones brain similar?

In the same way that computer CPUs can differ in speed, our brains could be thought of as having a clock speed of some kind. Clearly there is some speed, as in practical experience thinking does take time, it is not instantaneous. My question is - is this speed constant among humans - among westerners for example? Or do some people have brain-speeds that are say a half or a tenth of the average? Supplementary question - are there medical conditions or recreational drugs that can significantly slow down brain-speed? 78.145.21.210 (talk) 12:59, 12 May 2009 (UTC)

from the article myelin "The main purpose of a myelin layer (or sheath) is an increase in the speed at which impulses propagate along the myelinated fiber." It seems that the quality of the myelin varies see: http://www.medicexchange.com/Neurology-Brain-CNS/brain-images-reveal-the-secret-to-higher-iq.html --Digrpat (talk) 13:44, 12 May 2009 (UTC)

That Myelin article is I guess the closest you'll get to a hardware answer. My own experience is that I seem to have two speeds - very slow for thinking where someone says something and I don't have an answer ready and they're already on to the next thing before I open my mouth, and very fast where I can easily do things like catch a piece of paper dropped between my fingers. Yep I envy those people with a ready wit and repartee. Dmcq (talk) 15:19, 12 May 2009 (UTC)

I'm not sure clock speed is a good analogy. Whether or not one's brain chemically works at the same speed as others doesn't necessarily translate into speed of thought (associations, combinations of ideas, memory, mathematical operations—all of these are likely quite different neurologically). There are obviously some individuals who are really on the end of the bell curve in terms of some of these functions (John Von Neumann was reportedly a complete mathematical savant). I'm not sure there's any great way to measure the "speed" of the brain in general though. Keep in mind that even if you do measure the speed of a thought, it is not the same thing as the speed of your comprehension of the thought (which is another question altogether, neurological studies have shown—your brain knows things before "you" do). --98.217.14.211 (talk) 15:20, 12 May 2009 (UTC)

No. I am very slow witted. Some people are remarkably quick-witted, such as Paul Merton.--86.25.193.179 (talk) 16:14, 12 May 2009 (UTC)

As long as the brain is at normal temperature, the speed of the cellular components is fixed and the same for all people (it only takes a little bit of hypothermia to slow things down, though). But there is a concept of "processing speed" that operates on a higher level than the cellular, and possibly relates to intelligence. It isn't all that well-defined a concept, but you might look at this review for more information. There is a substantial amount of literature on the topic. Looie496 (talk) 16:15, 12 May 2009 (UTC)

Actually, clock speed might be a very good analogy. People often make the mistake of assuming the speed of a CPU is determined entirely by its clock speed, which is not the case, and the same mistake is being made here. The time it takes to solve a problem depends both on how many things you can do in a second and how many things you need to do. In terms of CPUs, a CPU can do one instruction for every tick of the clock, but different CPUs can do different amounts with each instruction. Some will have a special instruction to solve a given problem in one step while another would have to use general functions and do it in several steps. The same could be true of the brain - one person may be able to solve a problem quickly because they have a good method to do so while another person would take longer because their method is slower. Another factor in both brains and CPUs is memory, both the amount of working memory available and the amount of data already stored. A small child when asked to calculate "ten minus four" may take several seconds because they have to actually calculated it whereas I would answer in a fraction of a second because I have the answer stored in my memory having used it so many times before. The same happens with computers - really fast chess solvers often work by having the solutions to certain positions calculated and stored in advance (particular for the endgame when there are fewer possible positions). --Tango (talk) 18:09, 12 May 2009 (UTC)

There are people who speak very slowly. Are they slow witted? To some extent, this is a cultural thing. It may also be due to individuals copying others while growing up. Rural people and people from the American South supposedly speak slowly, though I have not noticed it. Some women speak very rapidly. I have heard Italian women rattle off Italian at amazing speed. - GlowWorm. —Preceding unsigned comment added by 98.21.108.29 (talk) 23:18, 12 May 2009 (UTC)

Italian needs to be spoken quickly — its information density per syllable is lower than that of English. Luckily, it can be spoken quickly, and understood, because its phonetics is extremely well-marked and unambiguous (for example, there are only seven vowel sounds, compared to I think around fourteen in English.) --Trovatore (talk) 23:24, 12 May 2009 (UTC)

That's an interesting concept, the information density of a language. I haven't heard of it before. Perhaps the speed develops over centuries by people taking short cuts in their speaking. It would be considered slangy or slurring at first, but when enough people do it, it would become respectable. It would be done because the speaker realizes the listener is a bit bored with long-winded speaking. GlowWorm. —Preceding unsigned comment added by 98.21.108.29 (talk) 23:35, 12 May 2009 (UTC)

No, I think it's the reverse: When you speak quickly you must speak very precisely, or you won't be understood. The "slurring" leads to high-information-density languages, spoken slowly. This is just my personal take on the matter — I haven't looked into the research on the matter, which I would expect has been well studied, but about which I don't really know anything from an academic point of view. --Trovatore (talk) 23:46, 12 May 2009 (UTC)

I have heard that a certain amount of "noise" (unnecessary words) is desirable in printed text to make it more comprehensible. This is sometimes done deliberately in children's books. - GlowWorm. —Preceding unsigned comment added by 98.21.108.29 (talk) 23:56, 12 May 2009 (UTC)

Even secondary-school books have a low information density. That makes them boring to brighter students. - GlowWorm. —Preceding unsigned comment added by 98.21.108.29 (talk) 00:07, 13 May 2009 (UTC)

OK, Trovatore. I get it now. Italian is spoken fast because it is low density now, not generations ago. That also necessitates few vowel sounds. - GlowWorm. —Preceding unsigned comment added by 98.21.108.29 (talk) 00:24, 13 May 2009 (UTC)

units

please help me with this question: if the units of force, energy and velocity are 10N, 100J and 5 m/s, find the units of length, mass and time.

(i just don't understand this, the unit of force is Newton. so what's 10N doing here?) please give me hints on how to solve this question —Preceding unsigned comment added by 122.50.131.1 (talk) 13:41, 12 May 2009 (UTC)

Is it that the question is asking you to suppose that something with that force and energy is travelling at that velocity. On that basis, it's asking you to work out how far it's travelled, what its mass is and how long it's taken to travel there. I have my reservations about this, because my science knowledge is sparse (and a more knowledgable contributor should be along soon) but I think you'd need one of "length" and "time" to work out the other. So perhaps I've misunderstood "length". It can't mean the length of the object, because unless there's more to the question than you've told us, it could be any length from just under infinitely long to just over zero length. --Dweller (talk) 13:57, 12 May 2009 (UTC)

It is a very confusing question, but here is my guess as to what it means. In SI (as well as in other systems of measurement), units of force, energy and velocity are derived units, defined in terms of the base units of length, mass and time, which are the metre, the kilogram and the second. But you could reverse this logic and make force, energy and velocity your base units, and then define length, mass and time in terms of them - for example, unit of length = unit of energy / unit of force (not a very practical approach, but possible in theory). So I think the question is asking this : in a system of measurement in which the base units are force, energy and velocity, and have magnitudes of 10N, 100J and 5 m/s, what are the magnitudes of the derived units of length, mass and time ? Gandalf61 (talk) 14:16, 12 May 2009 (UTC)

It's a horribly written question, but that interpretation seems to work. Allow me to explain it slightly differently in case people didn't get that. We define new units, Foo, Bar and Baz. Foo is a unit of force an is equal to 10N, Bar is a unit of energy and is equal to 100J and Baz is a unit of speed and is equal to 5m/s. If order to have a consistent system of units (so all the formulae we know still apply, for example F=ma, without needing to add in constants) we need to define new units of length, mass and time with particular conversions to SI units so that everything works out nicely. What should those new units be? --Tango (talk) 14:29, 12 May 2009 (UTC)

To me it sounds like a perfectly fair question. It does not require Energy, Force and Velocity to be the base units. All it requires is that their values turn out to be the ones described in the problem. Length, Time and Mass may still be taken to be the base units. I like that problem. Dauto (talk) 15:44, 12 May 2009 (UTC)

Yeah, it's a perfectly good question, just badly written. It should have said something like "If the units of force, energy and velocity in a new system of units are equal to 10N, 100J and 5 m/s, what are the units of length, mass and time equal to in terms of the appropriate SI units?". (That's assuming we have correctly interpreted the question, which is far from certain.) --Tango (talk) 18:01, 12 May 2009 (UTC)

I understood it first time around to mean what you're saying but agree it's poorly written Nil Einne (talk) 13:13, 18 May 2009 (UTC)

molecules and electrons

how can i find out the no. of electrons in 6.022 * 10²² molecules of methane?? —Preceding unsigned comment added by 122.50.131.1 (talk) 15:01, 12 May 2009 (UTC)

First find the number of electrons in one molecule of methane and than multiply that number by 6.022 * 10²² :) Dauto (talk) 15:51, 12 May 2009 (UTC)

Then check that you really mean 6.022 * 10²², and not 6.022 * 10²³. Algebraist 16:49, 12 May 2009 (UTC)

And consider whether you feel comfortable reporting the answer to four significant figures. Nimur (talk) 04:44, 13 May 2009 (UTC)

Are there methods which could increase or decrease the number of electrons in the specified material? Edison (talk) 05:17, 13 May 2009 (UTC)

Even methane plasma is still electrically neutral... Nimur (talk) 20:07, 13 May 2009 (UTC)

What's That Bug, episode 271,828,183

This thing is about 1.5 inches long, lives happily underwater (swims well, etc.), seems pretty happy out of the water, doesn't bite (me). I found it in a small stream in central North Carolina, USA. Anyone know what it is? Thanks. --Sean 15:20, 12 May 2009 (UTC)

File:BagginsBug1.jpg

What am I?

File:BagginsBug2.jpg

The underneath

Looks like a dragonfly nymph, but no idea what species. Mikenorton (talk) 15:58, 12 May 2009 (UTC)

Yeah, that's what I was about to say. Looie496 (talk) 15:59, 12 May 2009 (UTC)

Wow, no kidding; thanks so much. I just got schooled by a 5-year-old. :) --Sean 18:24, 12 May 2009 (UTC)

It looks like the nymph of some kind of darner. This photo (no species specified), looks pretty close. There are a bunch of other pictures of darner adults and nymphs by the same photographer here, but the nymphs of the different species look rather similar. Deor (talk) 20:40, 12 May 2009 (UTC)

What I have to say it really doesn't look like is something I would hold in my bare hand to take its photo. The abdomen reminds me of a tarantula hawk, supposedly one of the top-ranked insects for the pain induced by its sting. Presumably it isn't, since we haven't heard you screaming across the Internet. --Trovatore (talk) 00:15, 13 May 2009 (UTC)

I was going to post that Sean was uncommonly brave but didn't want to look like a milquetoast on, you know, an anonymous Internet forum. Thanks for beating me to it, milquetoast! Tempshill (talk) 02:58, 13 May 2009 (UTC)

Thanks, Deor. That looks just like it. The little booger lives in my pond now, so hopefully s/he'll stick around and eat mosquitoes and other villains. --Sean 01:37, 13 May 2009 (UTC)

Be sure to add it to Wildlife of North Carolina! We need more benthic macroinvertebrates. Nimur (talk) 20:09, 13 May 2009 (UTC)

electrons and molecules

how can i find out the number of electrons in one molecule of methane? —Preceding unsigned comment added by 122.50.131.1 (talk) 16:11, 12 May 2009 (UTC)

You could start by looking at our article on methane. 65.121.141.34 (talk) 16:21, 12 May 2009 (UTC)

You'll get close if you start by writing down the names of the atoms, then next to each atom write the number of electrons that atom normally carries. Tempshill (talk) 18:00, 12 May 2009 (UTC)

Remember to then account for the overall charge on the molecule. (Methane is usually neutral, but if you wanted to do a similar analysis for the sulfate ion, net charge becomes important.) -- 128.104.112.117 (talk) 23:21, 12 May 2009 (UTC)

How could the number of electrons be affected by ionization? Edison (talk) 05:15, 13 May 2009 (UTC)

By adding or removing electrons, you create a non-neutral molecule. Quite a trick to draw a simple Lewis or valence-electron structure for, e.g., "CH₄⁺", but such is life when you're doing mass spectrometry. DMacks (talk) 08:18, 13 May 2009 (UTC)

Removing COSTAR from Hubble

I don't really understand exactly how COSTAR can no longer be needed. So to begin with, I understand that Hubble had an aberration that required corrective optics in the form of COSTAR. Gradually old instruments have been replaced by ones that correct for the aberration themselves. How have the new instruments bypassed COSTAR? Is COSTAR something that can be turned on and off? Many thanks. RupertMillard (Talk) 18:02, 12 May 2009 (UTC)

To quote an official-looking page, "All the other instruments, installed since HST's initial deployment, were designed with their own corrective optics. When the FOC is replaced by the Advanced Camera for Surveys (ACS) during Servicing Mission 3B, COSTAR will no longer be needed." So appears that COSTAR has already been bypassed, and the last instrument needing correction is being replaced with one that does not need it.-RunningOnBrains 20:52, 12 May 2009 (UTC)

Yeah, but this is what I don't get — you stick something in a telescope to fix it. How can some instruments rely on it while others don't? RupertMillard (Talk) 21:09, 12 May 2009 (UTC)

They could have their own adaptive optics built in...just a guess though. -RunningOnBrains 02:00, 13 May 2009 (UTC)

I think the OP may be wondering whether the new instruments also peer through the same aperture as the old instruments. Tempshill (talk) 02:55, 13 May 2009 (UTC)

I think COSTAR's corrective optics can either be inserted into the optical path or stowed out of the way, but despite a good bit of searching yesterday, I was unable to find any sort of diagram showing this to be the case. -- Coneslayer (talk) 11:34, 13 May 2009 (UTC)

Yeah, that's exactly what I was driving at, Tempshill. I mean I had been trying to find out myself too. I guess I'll just have to settle for "that's just the way it is"! Thanks everyone for looking. RupertMillard (Talk) 20:18, 13 May 2009 (UTC)

(outdent) It finally occurred to me to use ADS instead of Teh Google, and I found an extensive article on COSTAR (click on "Full Printable Article" for the PDF). Page 22 contains an explicit statement that the COSTAR correctors can be deployed or retracted. -- Coneslayer (talk) 13:41, 18 May 2009 (UTC)

egg yolks

Are there egg yolks from some bird species that are not normally yellow as per chicken eggs? Examples? 65.121.141.34 (talk) 20:17, 12 May 2009 (UTC)

This BBC article (http://www.open2.net/everwonderedfood/eggsecrets.html) seems to suggests that 'crimson' yolks are said to occur if a hen is fed coloured maggots. Not quite what you mean but mostly on-topic. ny156uk (talk) 21:02, 12 May 2009 (UTC)

Indeed. The colour of egg yolks is largely mediated by the diet of the mother, therefore you feed any bird a different diet and you get a different yolk colour. Apparently Philippine duck eggs are known for their orange colour, due to an excess of ketocarotenoids in their diet, and ducks from the lake areas in southern China (such as Honghu, Jianli, Xiantao, Tianmen and Hanchuan in the Hubei Province) have red yolks due to rhodoxanthin in the pondweeds they eat. Rockpocket 17:02, 13 May 2009 (UTC)

Common liquids

I realised recently (like...2003, but meh) that there are very few household liquids that I know of; nearly everything is a suspension or solution in water. I can only think of:

• Water
• Oil (including petrol/diesel)
• Mercury

Are there many others that I'm simply ignorant of? 90.193.232.41 (talk) 20:50, 12 May 2009 (UTC)

That's an interesting observation! Another issue is that most things we use aren't "the pure chemical" but rather are dilute solutions or mixtures even if the material itself might be a liquid. DMacks (talk) 20:56, 12 May 2009 (UTC)

Mmhm. I noticed it when I realised milk was just water with suspended fat droplets; gravy was the same (water with something); so is pretty much everything I drink. What's blood? 90.193.232.41 (talk) 20:58, 12 May 2009 (UTC)

Blood is an aqueous solution with lots of cells and other things suspended in it. DMacks (talk) 20:59, 12 May 2009 (UTC)

At room temperature, there are e.g.:

• Vinegar (Acetic acid)
• Alcohol (Ethanol, Methanol, Propanol,...)
• Carbon tetrachloride

--Stephan Schulz (talk) 21:01, 12 May 2009 (UTC)

(several ecs)One reason I can think of off the top of my head as to why this is true: if you look at the phase diagram for water, you will see that the green liquid area is the smallest region on the graph; most substances are liquid only for a certain, relatively small range of temperature and pressure. Also, you have forgotten some that are probably in your house right now:

• Isopropyl alcohol (rubbing alcohol)
• Ethanol (drinking alcohol)
• cooking oil (very different structure than petroleum oils)
• glass (seriously)

Depending on what you mean by "household", there is also Hydrogen peroxide and Sulfuric acid. There are also many substances in your daily life which are kept as a liquid under pressure (even though they would be a gas if you released them from their container), such as 1,1,1,2-Tetrafluoroethane (probably cooling your refrigerator) and propane. -RunningOnBrains 21:22, 12 May 2009 (UTC)

Careful...the alcohols (especially drinking) in the home are almost certainly water solutions of these liquid chemicals. Likewise for peroxide and acetic acid. Pure sulfuric acid isn't even available at all. Cooking oil is a good household liquid (and important distinction vs the hydrocarbon oils and fuels). And from it we get biodiesel and similar liquids that are also different from hydrocarbon liquid fuels. OTOH, you'll want to read the glass#Physics of glass article to see what glass probably doesn't belong on a list of liquids. DMacks (talk) 21:34, 12 May 2009 (UTC)

I know glass isn't a liquid. I don't have "rubbing alcohol" (whatever that is) in my house. Aren't acids basically just a solution in water? =\ I guess I misunderstood chemistry in school...

Though they could be prepared as pure substances, both the acids and alcohols will almost certainly be solutions in water for any likely household use. Dragons flight (talk) 22:14, 12 May 2009 (UTC)

I usually have denatured alcohol at home (for cleaning). It's 95 or even 99% alcohol. I would not call this a "solution of alcohol in water", but rather "alcohol with impurities", or possibly "a solution of water in acohol". --Stephan Schulz (talk) 02:14, 13 May 2009 (UTC)

Perfumes and deodorants. Jay (talk) 09:59, 13 May 2009 (UTC)

A lighter may include a butane or naptha liquid. Dragons flight (talk) 22:20, 12 May 2009 (UTC)

Paint thinner / turpentine are other liquids in some households. Similarly, paints before application are usually liquid. Some paints are oil based, some are water based, and some are neither. Dragons flight (talk) 22:28, 12 May 2009 (UTC)

Courtesy of a slight Krazy Glue incident this evening, I got a chance to remind myself that the active ingredient in nail-polish remover is acetone (percent unstated on bottle). DMacks (talk) 08:14, 13 May 2009 (UTC)

Thank you very much for all the help, guys - this was exactly what I was after. ^_^ 90.193.232.41 (talk) 10:56, 13 May 2009 (UTC)

Most of the responses miss the OP's original point, which is a search for pure liquids one is likely to find around the house, not mixture or water-based solutions, but a substance that is a pure (or reasonably pure) liquid, and not a mixture of components. Almost everything listed above are clearly mixtures of multiple components. Nail polish remove is a water/acetone (or sometimes water/ethyl acetate) mixture. Paint thinner and terpentine are mixtures, as are most perfumes and cleaners. Even, strictly speaking, are cooking oils, which are not a single pure substance, but mixtures of a variety of triglycerides, composed of numerous different kinds of fatty acids. Water and mercury may sometimes be found around the house in pure forms, but beyond those two, you would likely be hard pressed to find any other liquids in your house which were not solutions or mixtures of some kind. --Jayron32.talk.contribs 15:20, 13 May 2009 (UTC)

Turpentine should be pure and 100% acetone nail polish remover is also available. Rubbing alcohol can be obtained for household use at 99% pure as well. The OP mentioned oil/petrol/diesel which are the same kind of mixtures as cooking oil and naptha so they should be acceptable also. Mineral oil is another such mixture that you may in your home. Taken to extremes, unless you stock fresh (and recently boiled) distilled water in your house that isn't pure either. If you still have carbon tet around your house, take it to your local hazardous waste handler. Rmhermen (talk) 17:45, 13 May 2009 (UTC)

For the record, cooking oil is NOTHING like petroleum oil. Petroleum is simple hydrocarbons, cooking oil is composed of substances like Triglycerides. But you are right to point out (as I had forgotten) that mineral oil is yet another different class.-RunningOnBrains 17:58, 13 May 2009 (UTC)

My reading of the OP was that he was looking for non-water-based liquids, rather than pure liquids. Dragons flight (talk) 17:50, 13 May 2009 (UTC)

I'm happy with mixtures, I just didn't want something which is basically a liquid purely because it's in some other liquid (something dissolved in water, for example). Alcohol is fine, even if not pure, as if you purified it it would be liquid. As would the components of petrol, if you separated them...I have assumed cooking oils would, too. 90.193.232.41 (talk) 23:20, 13 May 2009 (UTC)

magnetic rotation

Can one magnet using the repelling force of another magnet to create circular momentum of one of the magnet —Preceding unsigned comment added by 121.216.203.26 (talk) 21:30, 12 May 2009 (UTC)

It doesn't matter if it is repelling or attracting. Making one magnet move by use of another magnet is very common. The most visible example that comes to mind is dropping a magnetic cylinder in a liquid and placing it on a spinning magnet. The cylinder will spin also - mixing up the liquid. -- kainaw™ 22:35, 12 May 2009 (UTC)

The most common example of magnets attracting each other occurs in electric motors. —Preceding unsigned comment added by 98.21.108.29 (talk) 22:47, 12 May 2009 (UTC)

If our OP is asking whether there is some arrangement by which one magnet will keep another spinning against air resistance or friction - then the answer is a definitive "NO!" because that would be a perpetual motion machine. In the absence of air resistance and friction, a magnet can spin forever without the need to use another magnet to give it a continual 'push'. However, you could probably figure out some complex shape that would make one magnet start the other one spinning when you release them. But there is no such thing as a free lunch - the laws of thermodynamics guarantee that. SteveBaker (talk) 01:16, 13 May 2009 (UTC)

Redox

I need help understanding this task. I know that the charges on the periodic table go +1, +2, +3, +/-4, -3, -2, -1 (0), where 0 and +/-4 do not ionize (I think). But, what's the deal with the +e-? Honestly, I don't really know why some elements lose and gain electrons and some need that e-. Thank you. Sorry if this is a bit laborious. Thx! —Mr. E. Sánchez (that's me!)^{What I Do} / _{What I Say} 22:53, 12 May 2009 (UTC)

To a first approximation, atoms want their electron shells to look like noble gases (the octet rule), and they don't care which one. So they take the one that's easiest to get to. That is, the one where they have to gain/lose the least number of electrons, because each electron you gain/lose increases the overall charge, making it that much more energetically costly to gain/lose another. That's why the atoms on the left side of the periodic table tend to lose electrons, and the ones on the right gain electrons. It's the shortest, most energy-efficient path to be noble-gas like. (The whole analysis gets a little complicated in the transition metals, where there are electrons in the d-Orbitals which "don't count", but the general principle of being "noble gas like" still roughly holds.) -- 128.104.112.117 (talk) 23:17, 12 May 2009 (UTC)

Keeping strong alcohol in plastic bottles

I have a bottle of homemade Croatian moonshine slivovica, which I remember having a nice, slightly fruity smell and an okay aftertaste when it was new (once my throat stopped burning :) It still wasn't the most obvious tipple though, so about 3/4 of it ended up forgotten in a cupboard for the past year. I've just got it out and tried some, but now it has a much sharper smell and taste than I remembered. The bottle is plastic and was meant to hold mineral water, so I wondered if that was the cause. Could the spirit (which I guess is about 50% alcohol though I really have no idea) have leached any chemicals out of the plastic? 81.132.219.125 (talk) 23:38, 12 May 2009 (UTC)

Ethanol (alcohol) turns into ethanoic acid (vinegar) over time. Could it have been that? 90.193.232.41 (talk) 23:41, 12 May 2009 (UTC)

'Course, no one actually says ethanoic acid. It's acetic acid. Don't be pulled in by the useless silly IUPAC names. They'll never catch on, and this is a good thing. --Trovatore (talk) 07:44, 14 May 2009 (UTC)

It could have done I suppose, but wouldn't there still be a fruit smell? And wouldn't commercially produced spirits turn to vinegar in the same way, once the bottles had been opened? Thanks for answering btw :) 81.132.219.125 (talk) 23:48, 12 May 2009 (UTC)

Actually, now my glassful has been sitting out for a while, it does still have a fruit smell. The aftertaste is completely different though; it tastes like the smell of burnt plastic. If that makes any sense? 81.132.219.125 (talk) 23:51, 12 May 2009 (UTC)

I think there are a lot of possibilities, but I advise not drinking it -- alcohol is very powerful at dissolving stuff, and could conceivably be dissolving something from the bottle that you wouldn't want to be consuming. Looie496 (talk) 00:14, 13 May 2009 (UTC)

Use a glass bottle next time. Dauto (talk) 00:33, 13 May 2009 (UTC)

I know nothing about alcohol personally, but if our chemistry lessons were accurate in the real world, then yes - commercial spirits will also turn sour over time. 90.193.232.41 (talk) 10:53, 13 May 2009 (UTC)

Even water is known to leach residual chemicals from platic bottles. If you've ever left a water bottle in a hot car for a while, the water will take on a distinctive plastic taste. The presence of these chemicals are specific and quantifiable. See this study reported by the CBC. You can find other such studies around the web if you search, and it won't take long. I would imagine that alcohol, which is likely to be better at dissolving organic substances like plastics, would be expected to be better than even pure water at this, and thus it would easily be expected that alcohol stored in plastic over a long time could develop funny tastes. It may not be all plastics, but some will certainly impart unwanted flavors into your spirits. --Jayron32.talk.contribs 14:09, 13 May 2009 (UTC)

Cool, thanks a lot for the info. I wouldn't have drunk any more than the few sips I did, not when it now tastes so bad, but it's nice to know there's some sense in my uneducated guess :) 81.132.219.125 (talk) 22:38, 13 May 2009 (UTC)