Wikipedia:Reference desk/Science/February Werdnabot Archive

= February 16 =

"Biocompatible" article
Hey, upon reading the short article called "biocompatible", I realized that following the link "biomaterial" links off to some disambiguation page, which fails to clearly explain what it means. Looking at the context, it looks like the link should be to "bio-based material", but I'm not totally sure about this. What article do you guys think "biomaterial" should link to instead? --JDitto 03:04, 16 February 2007 (UTC)


 * I would guess biocompatible material. After reviewing some pages, I think that biocompatible material, biocompatible, and biocompatibility should all be merged into the latter. − Twas Now ( talk • contribs • e-mail ) 05:28, 16 February 2007 (UTC)


 * Oh no! Did I just cause another article merge? Oh well, I guess it's for the better.--JDitto 03:47, 20 February 2007 (UTC)

Telephone exchange
Any idea where on the web I would be able to get accurate information regarding the technology used in the telephone exchanges with respect to EC10B and OCB exchanges made by some French companies?


 * Plain old telephone service might be a good start. not sure though.  --Tbeatty 05:22, 16 February 2007 (UTC)
 * ok I don't really know but guessing maybe France Télécom or Alcatel-Lucent might give links to sites that have the answer.87.102.20.186 11:00, 16 February 2007 (UTC)

If a Compound
dissolves in water, is this a phyiscal, or chemical property of that Compound?--Honeymane Heghlu meH QaQ jajvam 04:23, 16 February 2007 (UTC)
 * Would it be both? Are they mutually exclusive? solvent is a pretty good article. i'd probably say it is the chemical properties of salt that allow it to dissolve in water, but more the physical properties of sugar that allow it to do the same. Vespine 05:16, 16 February 2007 (UTC)


 * Our article on solubility is categorized in Category:Chemical properties. − Twas Now ( talk • contribs • e-mail ) 05:21, 16 February 2007 (UTC)


 * The physical and chemical properties of a substance are one and the same thing. Chemistry is concerned with the distribution and movement of electrons, and this underpins all chemical processes. When, for example, sodium chloride dissolves in water the positive sodium ions and the negative chloride ions are interacting with the water molecules, with the sodium ions attracting electrons from the oxygen of the water, and the hydrogen ions of the water attracting electrons from the chloride ions. This is referred to as solvation. Sugar dissolving in water relies on hydrogen bonding but again this involves a movement of electrical charge.  Hexane2000 08:56, 16 February 2007 (UTC)

If a compound dissolves in water that's a physical property.

If a compound REACTS with water that's a chemical property.87.102.20.186 11:03, 16 February 2007 (UTC)

This question is getting at the difference between a physical change and a chemical change. Those article may help you out, though they could both use improvement. -- Beland 03:37, 18 February 2007 (UTC)

Crop failure...?
What percent of current crop production would have to fail and for how long before population growth would terminate? 71.100.10.48 04:46, 16 February 2007 (UTC)
 * It's impossible to predict with any precision. It partly depends on when the failure would occur. Population growth is already slowing due to concerns about overpopulation, and will likely eventually stop and perhaps reverse itself. (See Population growth.)  In theory, you could ask how many calories per day does a given population need to survive, and then try to calculate what fraction of the existing crops could support the current population, and how many "stored" calories are available in various places like supermarket shelves, grain silos, and animals.  It would depend on which crops failed, because different crops have different nutritional values.  It would also depend on what those crops were used for - animal feed, making bread, direct consumption, etc.  In practice, however, the political, economic, and social responses to a large-scale crop failure would greatly impact the survival rate.  Also consider that due to distributional issues, starvation is a problem even without widespread crop failures.  The article famine discusses some historic examples where millions of people have died, in some cases due to crop failures, which may provide interesting perspective on the answer to your question. -- Beland 03:47, 18 February 2007 (UTC)

String Theory article
Please clean up "String Theory" —The preceding unsigned comment was added by 212.183.136.192 (talk)
 * I assume we're talking about String theory? What seems to be the problem? DMacks 07:13, 16 February 2007 (UTC)


 * I'm not sure this is the place to ask for article cleanup. You could start at Talk:String theory, as well as Wikipedia talk:WikiProject Physics and Wikipedia talk:WikiProject Mathematics. − Twas Now ( talk • contribs • e-mail ) 09:07, 16 February 2007 (UTC)


 * We can't clean it up because no-one really understands it. &#x2013; b_jonas 20:03, 18 February 2007 (UTC)

Electrolyte process?
What is electrolyte process?


 * Could you be more specific? − Twas Now ( talk • contribs • e-mail ) 09:08, 16 February 2007 (UTC)

Shorter tendons, longer muscles; longer tendons, shorter muscles
The article tendon states that shorter tendons and longer muscles are more effective in terms of power generated/muscle mass. This question may seem a little odd but, (first question) is there any (as easy as possible) way to check which is my case? I've always seemed to have much more strength than my size suggested, but I'd like to know if this is actually true, maybe due to tendon size. (second question) Moreover, it is said shorter tendons are stronger but are they more prone (is this correct in English? :P) to injury? Thanks. --Taraborn 10:18, 16 February 2007 (UTC)

Bigfoot
In your most scientific opinion, is there a real possibility that there exists Bigfoot-type animals living in the non-human-habited forests or jungles of the world?


 * To my knowledge, there are no peer-reviewed scientific papers establishing the existence of such creatures, or verified accounts in newspapers or other sources. It seems difficult to judge definitively the probability of such creatures existing but not appearing in such sources. -- SCZenz 14:25, 16 February 2007 (UTC)
 * See also Formal studies of Bigfoot. One recent theory for Bigfoot's cousin Yeti, tries to attribute the cryptozoological phenomenon to brown bears because of their "proximity" to homo sapiens: They sometimes can be seen standing and moving upright, visit civilization for food raids and their footprints resemble human prints more than most animals'. ---Sluzzelin 15:11, 16 February 2007 (UTC)
 * Absence of evidence is not evidence of absence, but then, it isn't evidence of presence either.  --Bmk 23:24, 16 February 2007 (UTC)
 * I'm not sure that Homo florensis fits in the category of "Bigfoot-type animals" but take a look at Homo_florensis. --JWSchmidt 00:39, 17 February 2007 (UTC)


 * New extant species are still found regularly, though rate of discovery tends to be inversely related to the size of the species, for obvious reasons. New primates have been described over the last few years (e.g. Arunachal Macaque) and off course the Loch Ness Monster has still to be caught! Regarding proof of a Big-foot... most scientists would tell you it is improbable, but not impossible. Rockpock  e  t  07:06, 17 February 2007 (UTC)


 * Yeah - science isn't ready to say "No, this isn't possible" yet. Absence of evidence is not evidence of absence.  Without a detailed survey of unprecedented scale, I don't see how to prove that BigFoot is a myth.  Statistically, it seems very unlikely that they could have existed in the middle of such a closely studied and populated part of the world and not have been noticed regularly.  Even if they are shy - how come we find no carcasses of dead BigFoots - no skeletons - no fossilized specimens.  For Yeti, the case for them being a myth is much stronger.  The places they are claimed to inhabit are land-locked snowy wastelands that don't produce enough food to sustain a breeding population of such large warm-blooded creatures - so I think it's fairly safe to say that Yeti are mythical. SteveBaker 22:52, 17 February 2007 (UTC)

introduction to medical science
hi please can u help me with information on : generally the size of cells is limited to maintain a larger surface are to volume ration - why?

thanks for your help 196.209.46.158 14:24, 16 February 2007 (UTC)


 * Sounds like homework, but I'll give you a hint. If you have a humungous cell, how long does it take for molecules to go into the cell compared to a smaller cell? Splintercellguy 16:19, 16 February 2007 (UTC)

The effects of Global Warming on the UK
hello,

Am I right in thinking that due to global warming the UK is the only place on earth that is actually going to get colder? Is it going to be colder winters and warmer summers, because it seems that over the last few years that seems to be the case. Is the UK due to get more snow?

Thanks, --90.240.32.169 18:42, 16 February 2007 (UTC)


 * Not the only place - I'm assuming that the process to which you are obliquely refering would be if the Gulf stream were to switch off, leading to heating by this phenomena in the British Isles. At the very least this would cause cooling over much of Northern Europe, but most notably Scandinavia.
 * Please, please, please. That hasn't happened ever in the lifespan of the entire Earth, in which temperatures have both been much higher and much than in the near future. [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 08:01, 18 February 2007 (UTC)
 * If you don't mind me asking, how old are you? [I'm only 23!] I think that statistically the last couple of decades have been warmer than any previously seen, but the last few years may have seen more snow that the few years before. But consider - to my recollection there have only been two genuinely cold weeks so far this winter, which is really not a lot at all! One suggested outcome of global warming is that it may increase the incident of freak weather, i.e. a sudden snowstorm over consistantly cold and snowy weeks. --Neo 20:31, 16 February 2007 (UTC)


 * I believe the eastern United States has been cooling steadily but lots of places have been cooling. Not that you would have heard it on the news :).  There are lots of suggested outcomes of Global Warming mostly though it creates alarmism instead of representing scientific conclusions.  Tbeatty 05:41, 17 February 2007 (UTC)


 * I don't think the view is generally held that the UK will get cooler as the rest of the world gets warmer. Most climate scientists expect the UK to get warmer. However, there is a view that the effects of global warming in the UK will be less than elsewhere (see this article in The Times referring to the opinions of Prof James Lovelock). I agree with Neo that the last couple of decades have been warmer in the UK. January this year was the warmest since 1916, although this does make you wonder what was happening in 1916!. My personal view is that all predictions must be treated with caution. Hexane2000 07:59, 17 February 2007 (UTC)
 * Many areas in the world would likely experience colder winters due to the slowing of warm ocean currents caused by increased sea level. This is because, as the ice melts, it pours freshwater over the saltwater of the ocean, and since freshwater is lighter, it floats on top. Warming of the ocean could then raise the altitude of warm currents, embedding them within the freshwater. As warm water flows around the world, it often sinks and becomes cold. In some areas, if the cold water current flows in the direction opposite that of the warm water current, it could stall that current because freshwater cannot sink under saltwater, so it would also likely not have energy to flow against the current, and the current would pile up onto itself, eentually stalling it. If the current simply has to turn slightly where it would usually sink, it can easily flow in the correct position and not stall. Working currents will likely stay in the reigon, and would stop the transfer between warm and cold water. This would also cause some areas usually experiencing warm currents at mid-latitudes to experience colder winters, hotter summers, and dryer seasons. The gulf current is already cooling, and the Atlantic hurricane season could decline in areas other than the caribbean, due to a decrease in mid-latitude warm currents and an increase in the Sahara's aridity. Areas affected could include western Europe, northwestern USA, eastern Canada, Korea, Japan, northwestern USA, western Canada, eastern Australia, southern New Zealand, western Madagascar, southeastern Africa, and southeastern Brazil, Uruguay, and northeastern Argentina. So, no, it's not just the UK. Hope this helps. A  stroHur  ricane  00  1 (Talk+Contribs+Ubx) 20:37, 17 February 2007 (UTC)


 * The flooding is a serious problem too. Sea level rises of even tens of feet will turn most of London and the surrounding suburbs into ocean.  With something like 7 to 15 million people live in that area...the consequences are hard to imagine. SteveBaker 21:46, 17 February 2007 (UTC)

Zero Gravity
Is it possible to create Zero Gravity conditions at sea level on earth? Has this ever been attempted or done? If not, do you have any ideas how this can be attempted?
 * Zero gravity (actually microgravity) in orbit is not due to the spacecraft being far away from the Earth. It's because the craft is in free fall.  You can easily replicate that closer to Earth by putting yourself in free fall: simply jump from a high place as safely as you can.  A diving board or airplane (with parachute) are traditional, but the vomit comet works well, too.  --TotoBaggins 19:06, 16 February 2007 (UTC)

I was thinking along the lines of a man-made chamber, on the ground, on earth, in which one can step into and negate earth's gravity. Is that possible?


 * No, there is nothing like that, (if there was I'd have one in my house!) but there are things like Magnetic levitation, which can be used to levitate objects under certain conditions. GhostPirate 20:10, 16 February 2007 (UTC)


 * Unfortunately we don't (yet) have the ability to manipulate gravity fields. As noted, it's possible to suspend an object in midair by balancing the gravitational on it using another force.  You can use a vertical wind tunnel, in which aerodynamic drag lifts a person against the force of gravity.  If you have more money (and no metallic surgical implants...) you can use diamagnetic levitation.  If you're cheap, you can balance the force of gravity with a rope attached to some high point. TenOfAllTrades(talk) 20:16, 16 February 2007 (UTC)


 * Taking "sea level" quite literally, swimming or scuba diving is as close as you'll get. Your weight effectively becomes zero, so it amounts to the same thing as zero gravity.--Shantavira 09:22, 17 February 2007 (UTC)


 * None of these suggestions are zero gravity. Take a bottle with a marble in it into any one of these situations (Parachute, Magnetic levitation, vertical wind tunnel, diamagnetic levitation, a long rope or by going swimming) - and take a look at your marble.  In every single case, it'll sit firmly at the bottom of the bottle - held there by gravity.  So none of those approaches will create anything much like zero G.  Jumping off a tall building will get you (briefly) pretty close zero g - until wind resistance slows you to terminal velocity.  The Vomit Comet does produce a realistic zero-g environment - but nowhere close to sea level!  Some roller-coasters produce a brief zero-g experience.  There really isn't anything that's going to work for more than a few seconds though.  Maybe if you could take a suitably small black hole or maybe a neutron star and somehow suspend it a few hundred feet above your head then there would be a small region where their gravity would cancel out - but the tidal forces wouldn't be much fun.  So no, basically, we have no idea how to create zero-g here on earth. SteveBaker 18:04, 17 February 2007 (UTC)


 * If these guys are right, then their work has the potential to lead to the construction of an antigravity chamber by creating a localized gravitomagnetic field that opposes Earth's gravity. Their work, funded by the European Space Agency, is the first claim of an observable gravitomagnetic field created in a laboratory setting.  However, one should note that the fields are only just observable, a few micro-g for less than a millisecond over a volume of several cubic centimeters.  So they would probably have to scale it by more than a trillion times before even thinking about building a real anti-grav chamber.  (Not to mention that the cost of $10,000 in liquid He per run better not scale by a trillion.)  Also, I would point out that their work is quite new, and will remain controversial until verified (or refuted) by independent research labs.  Dragons flight 18:32, 17 February 2007 (UTC)


 * Yeah - that's interesting work. I'm not sure that mainstream science has accepted this yet.  But even so, as it says in that article:  "Although just 100 millionths of the acceleration due to the Earth’s gravitational field, the measured field is a surprising one hundred million trillion times larger than Einstein’s General Relativity predicts." - so if our theories are correct, we can theoretically make an antigravity machine negate 1/10,000,000,000,000,000,000,000,000th of a g.  Not really a practical zero-g machine.  Lugging a neutron star closer would be easier! SteveBaker 22:45, 17 February 2007 (UTC)


 * What about a very low, near see-level orbit (or just a high-speed maglev train around the Equator), and let the centrifugal force cancel gravity? It surely needs more speed than an airplane, but it's effect would last a lot longer. --V. Szabolcs 22:11, 18 February 2007 (UTC)


 * How about a small chamber attached to the ground, and ontop of that chamber ANOTHER EARTH. Yes. That would do the trick nicely. 213.48.15.234 10:32, 20 February 2007 (UTC)

Bioactive compounds
I really need to know the name and isolation of two bioactive compounds.

Thanks, Arguss 21:08, 16 February 2007 (UTC)
 * Er, huh? You want us to pick them and then tell you how they are isolated? How will our doing your homework help you learn? DMacks 22:14, 16 February 2007 (UTC)


 * How about reading Biological activity, to understand what you are looking for, then choose somthing suitable from Category:Lists of drugs. Rockpock  e  t  06:50, 17 February 2007 (UTC)

Rocket into Space
What will likely happen if you strap onto the end of a structurally-sound (enough to withstand this blast) space ship the equivalent of 1 billion nuclear bombs? WIll it travel faster than the speed of light?


 * Nothing can go faster than light. See special relativity. It will probably be close, though, if your ship isn't increadibly heavy together with being "structurally-sound". David [[image:Da Vit in Chu Nôm.jpg|23px|Da Vit]] 21:44, 16 February 2007 (UTC)


 * The number of bombs is irrelevant. It is the TNT equivalent that matters! A single gigaton bomb is 1,000,000 times more powerful than one billion microton bombs. But you probably mean something of about 20 Mt in TNT equivalence, or 20 "petatons". Yeesh! − Twas Now ( talk • contribs • e-mail ) 22:04, 16 February 2007 (UTC)

I thought it didn't matter how "heavy" a ship could be in space....


 * I think David meant "massive" (ie. if the spacecraft didn't have a large mass). - Akamad 21:58, 16 February 2007 (UTC)

Your rocket could have a force of 1 billion, 1 trillion, or even an infinite number of nuclear bombs, but it would still not have enough force to travel at or above the speed of light. As an object increases in speed, it decreases in length in the direction of travel, and increases in mass. This means that in order to travel at the speed of light, your spaceship would be required to generate an infinite amount of energy, which is, of course, impossible under your circumstances. Your nuclear bombs would have to take up an infinite amount of space to generate an infinite amount of energy, so your spaceship would have infinite size.

It is possible to move away from something at faster than light. This is because space's (meaning in this case the universe) expansion is NOT govered by the laws discussed above.

Hopefully this answers your question. I would sign my name, but I'm not registered on here. Just call me Thrawn.
 * It's not possible to move away from something at more than light speed either, from your own frame of reference. &mdash; Lomn 00:31, 17 February 2007 (UTC)
 * The original poster might be interested in Project Orion (nuclear propulsion), the hydrogen bomb-powered spaceship design that was in early competition (of sorts) with Wernher von Braun's chemical-rocket team that eventually prevailed and later became NASA. --TotoBaggins 01:19, 17 February 2007 (UTC)
 * Actually, the only thng that can move faster than light is space itself, with the expansion of the universe. A photon of light can travel at the speed of light because it is made of little mass and energy. Space itself contains little mass, and is filled with energy. Near the edge of the universe, matter is created, but is filled with always outgoing expandng energy. Therefore, if you compared a object at one side of the universe compared to the other, they could be moving apart faster than the speed of light. Since the theory of the expansion of the universe states that a celestial object far from another object will move away faster from the object than an object more closeby, the two objects I mentioned would be getting farther from each other, thus the speed would increase as the distance increased, because the further apart two objects are means the faster they move apart. This would thus give the possibly false impression that the universe is expanding faster than it used to. Hope this helps. Also, hope you didn't get as confused as I did. A  stroHur  ricane  00  1 (Talk+Contribs+Ubx) 20:01, 17 February 2007 (UTC)


 * The universe, according to all current observations, is expanding faster now than it did originally. Additionally I am not sure you are correct in saying that "matter is created but filled with energy" — the expansion of the universe does not create new matter; the spaces between matter are what are expanding. See metric expansion of space for more details. --24.147.86.187 20:50, 17 February 2007 (UTC)


 * See Is Faster Than Light Travel or Communication Possible?#Relativistic Rocket from the Usenet Physics FAQ. &#x2013; b_jonas 19:53, 18 February 2007 (UTC)

Chemistry
1. If an element contains two or more naturally occurring isotopes, is it a pure substance? 2. For compounds such as lead (II) iodide, when do you write the set of brackets and the Roman numeral in between them? Thanks very much for responding. 38.116.207.237 22:17, 16 February 2007 (UTC)

1. In chemical terms, yes. Isotope are essentialy chemically indistinguishable from each other, IIRC. 2. This number describes the ionisation state of the metal in question. It is only used for elements which are transition metals and have multiple possible oxidation/ionisation states. --Neo 22:27, 16 February 2007 (UTC)

Water
What are the dangers of water, such as floods and tidal waves?
 * See Dihydrogen monoxide hoax for 100% accurate, but somewhat distorted facts about this insidious killer. 75.45.91.230 02:19, 16 February 2007 (UTC)

Ok, but i need kinda like a list and description of what water can do or what it can make.65.6.118.206 02:54, 16 February 2007 (UTC)Student T.


 * Try drowning, water intoxication, tsunami, hail, Bull Connor, Burn (injury), landslide, black ice, waterboarding. Use your imagination and then look up the corresponding articles.  --Allen 03:08, 16 February 2007 (UTC)


 * It can drown you. It can disrupt your electrolyte balance if you drank too much. It could react quickly with a base or an acid and explode in a torrent of chemical burn-causing protein-denaturing liquid. It could knock down your house, causing the roof to fall on top of you. Someone could rig it to fall through a pipe and turn a lever that activates an electric chair, killing you. There are a potentially infinite silly and non-silly ways water can hurt you. Perhaps if you narrowed this down, it might help. Do you care about the chemical level, water reacting with things to create compounds that could hurt you? Physical level, where it kills you on a mechanical or chemical level, but on a larger scale? A level where it knocks down buildings (this seems to be what you're after, but again, there are many ways this could happen.)

For the latter, you might read up on tsunami, flood, tidal wave, global warming, ice sheet, ice cap, Noah's Ark, hurricane, and related subjects. --Wo o ty Woot? contribs 03:09, 16 February 2007 (UTC)
 * (edit conflict) Water can push things, crush things, float things, drown things, cool (or warm) things, wet things, dissolve things. Depending on what kind of thing and/or what kind of water you're talking about, one or more of those hazards will be "the dangers". DMacks 03:09, 16 February 2007 (UTC)


 * [another edit conflict]
 * You can drown in it.
 * When it freezes on a surface, you can slip on it and fall, or spin out in your car and maybe kill yourself.
 * If a bunch of it collects behind a dam and is suddenly released, the resulting flood can be devastating.
 * You already mentioned tidal waves.
 * If you drink too much of it in a radio station contest, you can die.
 * If a frozen chunk of it (such as a large icicle) falls on you, it can hurt you.
 * Its expansion while freezing can damage roads and structures.
 * Steam can scald you, or cause an explosion.
 * Erosion can undermine roads and cause collapse.
 * Water introduced into a subterranean clay layer on a hillside can result in a landslide.
 * Avalanches can be pretty serious, too.
 * The Chinese water torture is allegedly pretty horrible.
 * Water in the gas tank can keep your car's engine from running -- or in a plane's gas tank can cause the plane to crash, for example if some of the water freezes in the fuel line.
 * If you drive through a puddle of water too fast, your car's tires can hydroplane.
 * If you worked at it you could probably manage to cut your finger off with a water jet cutter.
 * Being hit with a snowball can really hurt, especially if your assailant dips it in water first.
 * If you're accidentally immersed in cold water, hypothermia can kill you.
 * Even though it's their home and they're designed to venture out on it, there are lots of things the ocean can do to damage or sink boats.
 * The pressure at the bottom of the ocean can crush the strongest of vessels.
 * If you are Penelope and you get run over by a steam locomotive, the results can be devastating (although granted, this is more the fault of the villain who tied you to the tracks than the locomotive's, much less the water and steam in its boilers).
 * If you pour water on sodium or other alkali metals, the results can be devastating. Likewise calcium carbide and calcium hydride, if the resulting gas ignites explosively.
 * Allegedly fresh, but actually not so pure, water can contain toxins which can infect you.
 * Water causes iron and steel to rust and other metals to corrode, causing endless damage.
 * When wood gets wet it often expands, damaging the structure it's part of.
 * Water is generally ruinous to artistic creations or other treasures made of paper (and also castles made of sand).
 * Rain or fog can drastically reduce your visibility, sometimes to the the point of causing accidents.
 * Water suddenly applied to hot pieces of metal or glass can cause them to crack.
 * If you stay in the bath too long, your fingers and toes get all puffy.
 * Water can short out and damage electrical circuits.
 * —Steve Summit (talk) 03:13, 16 February 2007 (UTC)

You forgot that if you compress and heat tritium, it will be a hydrogen bomb. :)  --Zeizmic 12:53, 16 February 2007 (UTC)


 * Further to Steve's last item, water can also convey electric shocks, allowing defective wiring to kill you without your touching it. Not to mention electric eels.
 * If water gets into a brake line and freezes, the brakes may stop working.
 * If you swallow a bit of water the wrong way and it goes down your trachea, the resulting coughing may distract you so that you step off a curb (or drive) against a red light with fatal results.
 * While you gaze at a famous fountain, your passport might be stolen by a pickpocket preying on tourists. The time to replace your passport might cause you to miss your flight home, after which either you get on a plane that crashes, or else your boss doesn't believe your story and you get fired, lose your medical insurance, stop having regular medical checkups, not discover that you have developed hypertension, and die of a stroke.
 * If your shoes get wet, they may shrink or otherwise be damaged. If you can't replace them, you might step on a sharp object and die of tetanus.
 * Your water bill might be the last straw that drives you over the line into bankruptcy.
 * If an structure is built too weakly, a heavy weight of water on top could make it collapse. This could be something like a hot tub or (as happened in New York in 1962) just waterlogged soil (due to a blocked drain) above an underground parking lot.
 * If a high vertical wall consists of multiple layers and it's possible for a thin layer of water to accumulate between them, the resulting hydrostatic pressure can drive the layers apart. This caused the failure of a concrete-and-steel storage tank under construction in Philadelphia in 1973. (Reference for this and the last item: ISBN 0-07-033565-6)
 * If someone drives through a mud puddle and splashes you or you get caught in heavy rain when you are about to go on a date, you might be too afraid of rejection to go through with it, and lose out on the love of your life. Or your super-rich but shallow-minded date might reject you, leading to you not inheriting a fortune when he dies.
 * Remember what the RMS Titanic ran into?
 * --Anonymous, February 17, 2007, edited 01:42 (UTC).

And if there is an earthquake water can flow up through mud and sand, so anything built on it could start to sink:)Hidden secret 7 10:57, 18 February 2007 (UTC)


 * And there's more:
 * If you add water to a strong acid, the result is not placid.
 * Highway departments in temperate climates often install water-filled barrels at the gore of an off-ramp to damp a collision if a careless or confused motorist can't decide whether to take the off-ramp or stay on the highway. If the temperature were nonetheless to drop below freezing for a time, such that the water in the barrel froze, it would have opposite than the intended effect in a collision.
 * Dampness in a basement promotes mustiness, mildew, and mold. (Also on shower curtains.)
 * Sitting in a barrel near the top of a cliff is generally safe. Sitting in a barrel (or boat) near the top of a waterfall is considerably less so.
 * The existence of watermarks on official paper stock can stymie you if you are intent on certain kinds of forgery.
 * A drop of water on a photographic film or plate will generally spoil it.
 * Watered-down gin smells just like full-strength gin, so someone drinking it can trick you into thinking they're less adept than they are.
 * If it weren't for the water added to initiate the curing process, the concrete overshoes which a mobster might force you to wear would be easier to escape from.
 * It's hard to measure a teaspoon of sugar into your coffee or tea, or put a cup of detergent in your washing machine, or sprinkle salt on your frozen sidewalk, if moisture has caused any of these materials to get all caked up.
 * If the wrong kind of snow, rain, or wet leaves accumulates on or near railways, operations can be adversely affected.
 * If you're a cop trying to arrest Mr. Incredible and Lucius Frozone after they've been wantonly rescuing people from a burning building, and you permit Frozone to take a drink of water, you're done for.
 * When the weather is hot, humidity makes it much more uncomfortable.
 * Water condensing out of humid air onto a cold surface can be a real nuisance, or worse.
 * If anyone ever manages to synthesize Ice-nine, we're in real trouble.
 * —Steve Summit (talk) 14:24, 18 February 2007 (UTC)


 * And of course if you're elected President of the United States and make a two-hour inaugural address in the rain, your resistance to disease might be lowered so much you die of pneumonia. (Okay, maybe it wasn't raining, but it would've been that much worse if it was.)  --Anon, Feb. 18, 18:04 (UTC).

Thx72.150.31.11 23:00, 19 February 2007 (UTC)Student T.

Holy crap, why isn't this stuff banned? 213.48.15.234 08:22, 22 February 2007 (UTC)

= February 17 =

Pulley
Consider an ideal pulley. What would happen if on one end of the pulley was a person, and on the other end was a weight of exactly the same mass, and this person pulled down on the rope? Now, my first conclusion was that the weight would go up, and the person would remain where he was. However, I don't completely trust my proof because it made a lot of assumptions which I'm not sure are right. Can someone help? Thanks.


 * You have not taken Newton's Third Law into account. --Anonymous, February 17, 2007, 01:03 (UTC).


 * Consider the center of mass of the whole system. The will not change because of internal forces, therefore both the man and the weight will go up an equal amount. Theresa Knott | Taste the Korn 12:53, 17 February 2007 (UTC)

Birds
What is the heaviest flying bird? Corvus cornix 00:11, 17 February 2007 (UTC)


 * Arguably the male Great Bustard. Have a look at the article for other contenders. --Kurt Shaped Box 00:17, 17 February 2007 (UTC)
 * Great, thanks. Corvus cornix 00:25, 17 February 2007 (UTC)


 * I'd love to see one of those birds up close. It's hard to visualize the scale from photos and videos. The largest bird I ever personally held was a great black-backed gull - now that is a *massive* bird (incredibly strong too). --Kurt Shaped Box 01:25, 17 February 2007 (UTC)


 * Have a look at this, too. Dr_Dima
 * Second thought. There is a surprisingly sharp "ceiling" on modern flight-capable bird weight, around 13-14 kilogram. See Bustard, mute swan, Dalmatian pelican, Marabou Stork, condor, monk vulture (incomplete list). Those named are in several orders of Aves so the weight similarity is not due to excessive genetic similarity, at all. What is the max weight limit due to, then? Energy balance (flight expenses vs food intake)? Wing load limit combined with overall size limit? Takeoff and landing? Unfeasibly slow rate of reproduction? Something else? The discussion in Argentavis (follow Kurt's link) is very interesting in that respect. However, it explains neither why large pterosaurs like pteranodon thrived for most of Cretaceous period, nor why Argentavis ever evolved to be a viable species. Any ideas? Dr_Dima.


 * Well, there are several factors limiting weight - but they almost all depend on the fact that when you double the 'size' of something (it's length, width and height all get twice as big), you quadruple its surface area and octuple its volume. So for nature to get a bird with twice the wingspan - you have to somehow cope with the fact that it got eight times heavier!  Wing area is an important measure of how well something can fly - but the wing area only quadrupled when the weight octupled - so the amount of weight each square inch of wing has to lift doubles when the size of the bird doubles...not good.  Worse still, the strength of a muscle depends on it's cross-sectional area.   So again, you double the size of the bird and the muscles get four times stonger - but you have eight times as much weight to lift using them.  When you work your muscles hard, they generate heat which has to be dissipated somehow...heat dissipation depends on surface area - so you can't easily make smaller muscles work harder because they'll cook.  There are lots of other consequences of this kind of length-to-area-to-volume thing - but all make life harder and harder the bigger your animal becomes.  Look at the graceful skinny legs of gazelle and compare them to the chunky stumps of elephants, hippo's and rhinos...same deal.  If you are twice as long a gazelle, you weigh eight times as much - so your legs have to be (proportionately) four times as thick to support your weight.  The largest pteranodons are thought to have spent most of their time gliding.  That helps a lot of these problems because you only need large enough wing area - you don't have to cope with the musculature and skeletal issues of true flapping flight.  SteveBaker 22:35, 17 February 2007 (UTC)


 * I don't know if this is the current theory or not - but it used to be suggested that giant flying creatures could exist in ancient times because the oxygen content of the air was supposedly higher back then, allowing for a faster metabolism. --Kurt Shaped Box 22:50, 17 February 2007 (UTC)


 * That's substantially older, though - we're talking the Carboniferous period, long, long before birds evolved. Those were still probably smaller than these birds; the oxygen wasn't beneficial because it gave a higher metabolism, but because the higher pressure allowed insects to grow larger. (Insects require oxygen to diffuse around their body; it's not blood-circulated like in animals. As such, after a certain size they just wouldn't be able to breathe... unless the oxygen pressure was higher)
 * As to enormous birds, don't forget the Eurasian Eagle-owl. Remarkable beasts. Shimgray | talk | 01:25, 18 February 2007 (UTC)

What makes pop rocks pop?
Ok, I know from the article and personal experience that saliva releases the CO2, and that's what makes them pop, and I'd always assumed that moisture did it. But I was in baskin robbins today, and I saw that they had a flavor of ice cream with pop rocks in it, and if it's moisture that does it then why don't they all finish popping while in the ice cream? Thanks for helping with my weird musings. 68.49.175.198 00:56, 17 February 2007 (UTC)
 * Well-frozen ice cream is not particularly moist, as the water content is in fact frozen. Consider putting some pop-rocks on an ice cube.  They would almost certainly not pop.  --TotoBaggins 01:24, 17 February 2007 (UTC)
 * That, and as a chilled pop-rock started dissolving and popping, it would develop a coating of thick almost-solid sugar syrup which would prevent further entry of moisture. Unlike with icecream, your saliva isn't already full of sugar. --Wjbeaty 13:11, 18 February 2007 (UTC)
 * As I'm not an American I was wondering what the heck a pop-rock is so I did a search and found this page which may interest you both Nil Einne 14:37, 17 February 2007 (UTC)

“Gira” bird
Sorry, this is a hard one (at least for me): I am trying to find the scientific name of a bird I saw at the Montreal Biodome, the guide called it a “gira” (“jeera” but not “djeera”). He also mentioned it looks like a roadrunner and that it’s a recent addition to the ecosystem. Since the part of the ecosystem it was in is the tropical rainforest of America (mostly South America but also Central America) it comes from there. I’d personally describe the bird as very similar to a Great Lizard-Cuckoo (Saurothera merlini) but with a more brown appearance and a pale brown crest. It also has a big black tail with white spots. If it helps there were three birds that stayed together and looked curious. Hoping you can help me. Thanks in advance. Pro bug catcher (talk • contribs). 05:11, 17 February 2007 (UTC)


 * A search using the Biodome search form suggests colaptes auratus. --Shantavira 13:24, 17 February 2007 (UTC)


 * Colaptes auratus is not a tropical bird of South or Central America, does not look like a Great Lizard-Cuckoo (Saurothera merlini) and certainly doesn't have a crest. But thanks for the try. Pro bug catcher (talk • contribs). 02:52, 18 February 2007 (UTC)

Matter Waves
I have seen in T.V that when a particle moves with velocity faster than that of light (c), it goes back into time; i.e. it goes to the past. Is it true? If it is true, then what is the case with matter waves? Matter waves are also particles and they travel with velocity greater than that of light, so why don't they travel back in time??? —Preceding unsigned comment added by 122.168.82.87 (talk • contribs)


 * They don't travel faster than c. The De Broglie hypothesis says that all matter has wave-like properties, even if those properties are imperceptible unless said matter is "near c". There's no special 'matter wave particle' (any particle of matter will do), and matter still can't exceed c. -- Consumed Crustacean (talk) 07:31, 17 February 2007 (UTC)


 * Firstly, "time" is either constant or non-existent. It is a frame of reference created by humans to denote rate of change (and previous states) of all the atoms in the known universe. One "second" later, most atoms are in a different state and position. Therefore it is not possible to get back to a previous state (back in time) as the odds are against you... 1 in 1087 at current estimates. Secondly, with current scientific understanding, c is really the speed limit of our universe. Travelling faster than c is a misnomer. You can theoretically "warp" space to get from point A to point B faster than the speed light would have taken to get there, but this requires massive energy and undiscovered science for "compression and decompression of space". Sandman30s 07:54, 17 February 2007 (UTC)


 * Regarding your "velocity faster than that of light" comment, the tv programme was probably referring to tachyons, which are entirely hypothetical (and nothing to do with wave-particle duality, which are your "matter waves"). Essentially the theory goes that the speed of light is a cosmic speed restriction that nothing can pass. The matter we are familiar with all travels slower than lightspeed, so can never accelerate to c and so never travel faster than it. Conversely, any tachyons that existed would have speeds faster than c, so they could never decelerate to c and so never travel slower than it. Whether such a particle would be going backwards or forwards (or even standing still, depending on your reference frame) in time is as open as whether you can walk forwards or backwards in space from where you are now. Spiral Wave 17:05, 17 February 2007 (UTC)


 * The trouble with this question is that almost all of your premises are bogus: I have seen in T.V that when a particle moves with velocity faster than that of light (c), ...according to all accepted theories, nothing can go faster than light... it goes back into time; i.e. it goes to the past. ...no - if you  plug a velocity faster than c into the Lorentz transform in order to figure out how time changes for the particle the result is a complex number not a negative number.  If the answer was a straightforward negative number then Einstein (and pretty much everyone since) would not be saying "Nothing can go faster than the speed of light" - we'd be saying "If something could go faster than light, it would go backwards in time".  But the result isn't a negative number - it's the square root of a negative number - which is something that cannot exist.   This is why the speed of light is a universal speed limit.  So....Is it true?....no, it's not.  If it is true, then what is the case with matter waves? well, it's not so there is no question to answer - but....Matter waves are also particles and they travel with velocity greater than that of light, - I don't know what you mean about "matter waves" - matter and energy are just two sides of the same coin.  Nothing travels faster than light...nothing whatever...not even 'information'.   so why don't they travel back in time??? ...because your question is based on many false premises and is therefore not answerable. (Just like: "When did you stop beating your wife?"). SteveBaker 17:47, 17 February 2007 (UTC)


 * While the Usenet Physics FAQ doesn't have this specific question, it generally explains lots of things about special relativity quite well, so I recommend you to read it. &#x2013; b_jonas 18:59, 18 February 2007 (UTC)
 * In specific, for matter waves, see Is Faster Than Light Travel or Communication Possible?#Rigid bodies. &#x2013; b_jonas 19:02, 18 February 2007 (UTC)


 * I recall a particle physicist explaining that electrons and positrons are equivalent, except for the way they experience direction of time (in the context of creation and annihilation with a mediating virtual photon). But as far as I am concerned, this is a silly way to think of time.  You can start stretching the language and can describe anything as anything else.  Alternative explanations of the exact same phenomenon exist which do not beg for time-reversal.  Nimur 19:13, 18 February 2007 (UTC)

Peels
The peels of vegatables and fruits should be eaten because that's where most of the minerals and vitamins are located; does this apply to carrots? And baby carrots? Responses on my talk page would be greatly appreciated.100110100 08:36, 17 February 2007 (UTC)
 * Yes definitetly to carrots. Generally, the thing to do is to not peel a carrot rather then eating the peel (of whatever fruit). Really the only time it's necessary IMHO to peel is with unscrubbed potatoes or when potatoes are used for mashing. Not thinkin of hard skinned fruit like kiwifruit, bananas etc of course Nil Einne 15:01, 17 February 2007 (UTC)


 * Yeah - I agree, I believe the reason is that many vegetables grow by cell division mostly around the outside of the vegetable - so all of the nutrients are concentrated near the surface. The flavor of even mashed potatos can benefit from the skins.  My wife (who is French and therefore knows how to cook amaxingly well at some deep genetic level) removes the skins of baked potatos - uses the flesh of the potato to make mashed potato in the usual way - then tosses some of the skin into a blender so they are chopped up really small then mixes them into the mash.  I think it really helps the flavor. SteveBaker 17:36, 17 February 2007 (UTC)


 * Even when mashing potatoes, if you have a potato ricer, you needn't peel them; very little of the peel will get through the ricer.


 * Atlant 18:01, 20 February 2007 (UTC)

Casting
The casting article says, in the "plaster casting (of metals)" that the plaster is cracked away after use. It also says once prepared, the mould can produce 1-10 units per hour per mould. Please help! Thanks, Bioarchie1234 10:54, 17 February 2007 (UTC)
 * I've just read what I've written and I've realised I may not have made myself clear with the above. I meant that if the mould is cracked away after use, how can it make up to 10 units per hour per mould? Sorry for any confusion caused. Bioarchie1234 11:19, 17 February 2007 (UTC)
 * It's badly written - sometimes the moild is destroyed getting the casting out. However if the mould is in two or more parts then it doesn't have to be broken to get the casting out - and can be used again.87.102.7.220 14:19, 17 February 2007 (UTC)
 * Alternatively it might mean that 10 plaster moulds can be made per hour - typically the plaster would be poured round a rubbery model of the cast - allowed to set - the rubbery model can be removed, when the plaster is fully set it can be used for casting.87.102.7.220 14:22, 17 February 2007 (UTC)

Transformer
Please tell me how current passes through a transformer without any change,further there is no any electrical connetion in a transformer —Preceding unsigned comment added by 203.135.2.42 (talk • contribs)


 * See our article on transformers. Through electromagnetic induction a transformer uses the current in one circuit to generate a current in a second circuit, at a different voltage. No physical connection is required between the circuits, because energy is transferred between the circuits through the electromagnetic field - in exactly the same way as radio waves create a current in an aerial. Gandalf61 13:04, 17 February 2007 (UTC)


 * Allow me to just pick one nit (and it's somewhat pedantic to do so). The magnetic field generated by the primary induces an EMF (almost the same thing as voltage, and for most intents considered the same) in the secondary.  See Maxwell's equations and specifically Faraday's law of induction.  This is why the simple linear dependent source circuit model of the transformer uses a dependent current source for the primary and a dependent voltage source for the secondary.  Another nit, transformers don't have to change the voltage at all, isolation transformers usually have a 1:1 turns ratio. -- mattb


 * How meaningful is it to say that a transformer acts "in exactly the same way as radio waves create a current in an aerial"? As far as I know (though I could be wrong) a high-power broadcast antenna is modulated at a potential of thousands of volts, but at the receiving antenna typically mere microvolts are picked up.  Yet there is no turns ratio to explain this.  (I grant that both radio transmission and transformer conversion both involve electromagnetic fields, but to me the application regimes seem very different.) —Steve Summit (talk) 14:00, 17 February 2007 (UTC)


 * In an iron-core transformer, the magnetic field that is created is essentially contained in the iron core. The secondary coil 'sees' essentially the entire field created by the primary; we assume that there's very little loss to make the math easier, and it generally works pretty well.  With radio waves, only a pathetically small fraction of the field interacts with your antenna.  That's kind of hand-wavey, but you get the idea.  TenOfAllTrades(talk) 18:20, 17 February 2007 (UTC)


 * The original questioner seemed to be puzzled by the lack of a physical connection between the primary and secondary circuits in a transformer, and my point was that you do not need a physical connection, any more than a radio receiver needs to be connected to the transmitter. Iron core, coil design etc. in the transformer is there to make it more efficient, but the underlying principle of transferring energy through an electromagnetic field is the same as the more familiar application of radio transmission. Our article on radio frequency induction explains this principle, and links to both transformer and radio antenna. Gandalf61 22:21, 17 February 2007 (UTC)


 * Perhaps this 'laymans' explanation might help: You probably know that if you take a nice chunk of metal and wrap wire around it enough times, you can make an electromagnet...apply power - you get magnetism. Now - you probably also know that if you wiggle a magnet around near a coil of wire, you get electricity produced in the wire (that's the way a generator works for example).  So - if you wrap two wires around a common metal core (which is what a transformer is) - then when you put A/C current through one wire, you're making an electromagnet.  That means that the electromagnet generates electricity in the other coil - hence electricity is consumed in one coil and created in the other allowing power to pass from one to the other without the wires physically touching.  This is a horribly simplistic explanation - but it gives you a 'gut feel' for what's going on. SteveBaker 17:28, 17 February 2007 (UTC)

I'm not sure if this is what the Original Poster was asking, but an interesting aspect of transformer behavior is: they (mostly) conserve energy. If you don't draw any power out of the secondary of a transformer, it doesn't draw any power out of its power source. In fact, little or no current flows at all. But this can seem very strange. If you ignore the fact that the primary is a coil of wire, if you think of it as just a wire, it looks like the primary forms essentially a short across the power source -- so how can no current flow?

The answer, of course, is that the primary is not "just a wire"; the fact that it's a coil makes it act very differently from a plain wire. In particular, it's an inductor, and an inductor (like a capacitor) presents a nonzero impedance to an alternating-current circuit. Depending on the inductance of the coil and the frequency of the power source, the impedance can be so high that essentially no current flows. (A transformer coil would, on the other hand, look lke a short or a low-value resistance if you connected it to a direct current source. Among other things, this is why there are no DC transformers.)

Of course, when you do begin to draw power out of the secondary of a transformer, significant current does begin to flow in the primary, because now the primary isn't acting as a simple high-impedance inductor any more. —Steve Summit (talk) 19:18, 17 February 2007 (UTC)


 * Not to be contrary just for the sake of being so, but the reason there are no DC transformers is plainly and simply because of Faraday's law, expressed here as one of Maxwell's equations:


 * $$\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}} {\partial t}$$


 * I'm not disagreeing with anything you said, just pointing out that there's no need to complicate the matter. There are no DC transformers because (classical) electromagnetic induction doesn't happen without a time-varying magnetic flux with respect to some frame of reference.  It's not a matter of practicality, it's simply that transformers don't work without time varying current. -- mattb

Gametic disequilibrium calculation
How to calculate Gametic disequilibrium D'?. we are given the following values :p(B)=2.5, p(AB)=.5 and p(AA)=.5.

131.220.46.22 13:57, 17 February 2007 (UTC)


 * This web page explains it pretty well: http://darwin.eeb.uconn.edu/eeb348/lecture-notes/two-locus/node2.html - if that's not enough to get you going, let us know and I can explain in more detail. SteveBaker 17:21, 17 February 2007 (UTC)


 * Are gametic disequilibrium and linkage disequilibrium synonymous? If so, then someone can create the appropriate redirect.  (I don't want to do it myself, as I'm not certain that there isn't a subtle technical point of difference I'm unfamiliar with.) TenOfAllTrades(talk) 18:14, 17 February 2007 (UTC)

"Isotope-ions"
Is there such thing as an atom being an isotope and an ion at the same time? Thanks for responding. 208.72.125.203 17:51, 17 February 2007 (UTC)


 * Any given atom will be a particular isotope; any atom with a net charge (more or fewer electrons than protons) is an ion. So, yes. TenOfAllTrades(talk) 18:06, 17 February 2007 (UTC)

Beta particle emission
Why does atomic number of an element increase when nucleus of that element emits a particle? Consider Uranium with atomic number 92. It means that it has 92 electrons.When it emits beta particle its atomic number will become 93.But as it has lost one electron its atomic number would have decreased.But this doesn't happen.Why?Please tell me in detail. —Preceding unsigned comment added by Viraj47jagtap (talk • contribs)


 * Beta decay occurs when a neutron is transformed into a proton. Atomic number is determined by the number of protons, and hence increases.  Dragons flight 19:07, 17 February 2007 (UTC)


 * Dragons flight&mdash;I changed a typo in neutron for you. Hope you don't mind. TenOfAllTrades(talk) 20:30, 17 February 2007 (UTC)


 * Beta particles are electrons/positrons. Beta decay is when a neutron is transformed into a proton, electron and a neutrino.  The net change in charge (and momentum) is 0 but the electron and neutrino is ejected from the nucleus leaving a proton.  The atomic number increases but the mass number remains unchanged.   --Tbeatty 05:35, 18 February 2007 (UTC)


 * It's a trick question. Atomic number is the number of protons in the nucleus. In chemical equilibrium this also happens to be the number of electrons, that "orbit" the nucleus. In bets decay, one of the neutrons in the nucleus splits into a proton and an electron. in your example, we now have a total 93 protons and 93 electrons. But the almost all of the energy of the beta decay ends up as kinetic energy of the new electron, so the new electron leaves teh nucleus (and the atom) with great speed. The atom is now an ion: it is positively charged. It will eventually equilibrateby grabbing an electron somewhere. So we started with 92 electrons and we ended up with 93 electrons, even though we expelled an electron at one point. -Arch dude 01:36, 19 February 2007 (UTC)

Planetary Orbits
It is relatively easy to find information on the speed of every planet's orbit around the sun (year) or the time taken for the planets to rotate around their own axis (Day). And the same is true of how large the orbits are (Distance from the sun) but what is harder to find out is what direction they rotate in. Ideas such as up and down are all relative in space but if you look 'down' at the solar system so you can see Earth's North Pole which way do all the planets revolve and orbit? Do they all go the same way? Is it clockwise or anticlockwise?Simondrake 20:12, 17 February 2007 (UTC)
 * The "Orbital characteristics" section in the right-hand infobox on each planet's page describes its orbit in excruciating detail. You can click on the name of the orbital parameter (e.g., "semimajor axis, inclination, etc.) to see what each one means.  A good beginner's astronomy book, or a thorough reading of orbit, might be helpful.  --TotoBaggins 21:40, 17 February 2007 (UTC)
 * Planet has some tables at the bottom that covers much of this. All of the true planets orbit the sun in the same direction.  Whether you consider that 'clockwise' or 'anticlockwise' depends on whether you are looking from 'above' or 'below' the plane in which the planets predominantly orbit...but since there isn't an "up" or "down", it's completely arbitary which you think of it as.  But if you were looking down on the Earth's North pole, all of the planets would be orbiting in a counter-clockwise direction.   The 'icy dwarf' (not officially a planet - but still a big ball of dirt) called 'Erin' orbits in the opposite direction...but I think it's the only one.  The planets all spin on their axes in the same direction (counter-clockwise as seen from above the Earth's North pole) - with the exception of Uranus and Venus which spin clockwise. Both of the larger icy dwarfs (Pluto and Erin) spin in the 'wrong' direction too.  All of the planetary orbits lie pretty close to the same plane - so the solar system is pretty much a flat disk...except (again) for one of those annoying icy dwarfs - Pluto's orbit slants at quite a steep angle compared to the others. http://janus.astro.umd.edu/javadir/orbits/ssv.html is a nice animation showing the orbits - you can even watch asteroids, comets and kuiper-belt objects...neato.  SteveBaker 22:19, 17 February 2007 (UTC)


 * The section on retrograde rotation in our article on retrograde motion says: "Most planets, including Earth, spin in the direct sense: they spin in the same direction as they orbit the Sun (that is, their north rotational pole and north orbital pole point in similar directions, more or less in the direction of the Solar north pole). The exceptions are Venus and Uranus." Gandalf61 22:09, 17 February 2007 (UTC)


 * You may want to read the protoplanetary disc and solar nebula articles to understand how the planets formed from a single flat disc spinning around the Sun. That's why they all go the same way, as explained above. For the same reason, multiple extrasolar planets orbiting the same star will all head in the same direction as each other too. Planet obliquity or axial tilt is rather more complicated and the explanations differ from planet to planet, because other factors can change it after a planet has formed. Among the regular planets, Venus is 'upside down' as noted above, while Uranus is spinning on its side (and also technically upside down, since the tilt is over 90 degrees). Spiral Wave 22:34, 17 February 2007 (UTC)

Cell transport
÷Why is it important for intravenous fluids to be of the same solute concentration as human blood?
 * Presumably so that osmosis does not cause a massive change in blood pressure, but I'm no humorist. --TotoBaggins 21:45, 17 February 2007 (UTC)
 * Not all IV fluids have the same solute concentration as human blood; some are higher (e.g. hypertonic saline (3%) used (cautiously) in treatment of severe hyponatrema), and some are lower (e.g. 1/2 NS (0.45%)). What is important is that the IV fluid be appropriate for the clinical situation. The electrolytes need to be kept within a relatively narrow range, which is possible only if IV fluids of the right type are used appropriately. - Nunh-huh 03:07, 18 February 2007 (UTC)
 * See also Cytolysis and Water intoxication. -- Beland 04:32, 18 February 2007 (UTC)

Pterosaurs and pterodactyls
Quick question: What is the difference between a pterosaur and a pterodactyl? I've heard the terms used interchangeably in common usage. --Kurt Shaped Box 22:55, 17 February 2007 (UTC)


 * Our Pterosaur article suggests there's no difference. A dictionary I just checked suggests that pterodactyls and pteranodons are both specific families or genera of the order Pterosauria, although it also says that, informally, "pterodactyl" is often used as a synonym for "pterosaur". 141.154.214.254 04:32, 18 February 2007 (UTC)


 * Isn't there a difference as far as how the wing is formed? The "dactyl" part of pterodactyl indicates that the wing is an extended finger, whereas other pterosaurs may have had different wing structures.  Corvus cornix 21:00, 18 February 2007 (UTC)

How many fingers am I holding up?
Actually my question is what kind of trauma victims do people ask that question to? Other tests I know involve being able to focus on and follow an object across their field of vision and being able to see something at the periphery of their vision. I thought it was for people with possible serious concussions. I'm having a memory blank. 71.226.56.79 23:59, 17 February 2007 (UTC)
 * Those are just neurologic evaluations. They are particularly important when a neurologic injury is suspected (head trauma, stroke, etc.), but are actually more or less standard for any patient. - Nunh-huh 03:01, 18 February 2007 (UTC)
 * Also, the flashlight in the eyes test is to see if their pupils change size in response to the light. [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 07:38, 18 February 2007 (UTC)


 * And then there's The Soldier Who Sees Everything Twice from Joseph Heller's Catch-22.


 * Atlant 18:10, 20 February 2007 (UTC)

= February 18 =

Wikipedia questions
1)Does Wikipedia recognize wikispecies or ITIS (www.itis.gov) reports as a final arbiter on difficult taxonomic classification decisions?

2)When wikipedia has pages that are in conflict with both of those sources, what is the appropriate response for a wikipedian to take?Peter 06:25, 18 February 2007 (UTC)


 * Wikipedia talk:WikiProject Tree of Life is the best place to ask these sorts of questions. —Pengo 08:02, 18 February 2007 (UTC)
 * 1. Not necessarily either.
 * 2. Check the correctness of the wikispecies and ITIS info. ie look for references - read them. If there is a discrepency between two sources it may be worth noting that in the text.87.102.9.240 15:37, 18 February 2007 (UTC)

this is about the topic super conductivity....
i am a college student.. here in the philippines and im currently conducting some reasearch about superconductivity and i was really hoping that you might extend your hand to help me out with this topic.....

my research evolves on whether it is possible to use super conductors in making elivated cars.... or in that matter... what concepts can be useful in making elivated cars possible.... (anti-gravity cars..)

please send your answer in my email.... and i would be very much thankful... to hear from you soon...... here's my email;.... 

thank you.. and God bless...


 * Superconductivity has not been achieved at any temperature close to normal room temperature. It has only been done at temperatures near absolute zero, so I don't think that a car elevated by Superconductivity would be possible with the current level of technology. GhostPirate 12:39, 18 February 2007 (UTC)
 * That's not true. We have superconductors that work up to 92K - which could be achived with liquid nitrogen. SteveBaker 19:03, 18 February 2007 (UTC)
 * You may get further by studying maglev technology, although this has its own set of problems and might not be going far.--Shantavira 13:49, 18 February 2007 (UTC)


 * See High-temperature superconductivity --Tbeatty 18:42, 18 February 2007 (UTC)


 * The problem with all of this is not the "HOW" question but the "WHY" question. The two benefits of levitating cars might be as follows: (1) Reducing friction in an effort to get better fuel economy and (2) Removing the need for roads and tires that wear out.  However, there is no doubt that the energy costs in levitating a car would by far exceed the benefits in fuel savings (at any reasonable speed, air resistance exceeds rolling friction by a sizeable margin).  In a typical modern car, at top speed 35 horsepower is required to overcome rolling resistance and maybe 120 horsepower is for overcoming air resistance.  At much lower speed, it's nearer 50/50.  I'm a MINI Cooper fanatic and I wrote a paper about this outlining all of the math .  Whilst getting rid of roads would be neat - if you have to lay metal superconducting magnets or coils or some-such down instead - that's not going to be a cost-effective thing.   There are also very serious stability and safety issues.   If you've ever tried to drive a hovercraft, you'd know that they have terrible lateral stability and they don't corner worth a damn - you'd need to run your hovering cars inside some kind of track arrangement.  It's truly not worth the hassle.
 * Having said that - mag-lev or superconducting levitation trains are a very practical proposition. That's because they have much more significant rolling resistance than cars (hundreds of wheels instead of just four!) and their aerodynamic cross-section is hardly any bigger than a car.   So for a train, getting rid of the rolling resistance might be worth it...but not for a car. SteveBaker 19:03, 18 February 2007 (UTC)


 * I'm glad somebody has investigated rolling friction vs. aerial drag - I recently got into a heated debate about which was the more relevant engineering challenge (I think I was wrong, in light of SteveBaker's numbers :) Nimur 19:25, 18 February 2007 (UTC)


 * I think it depends on how far out you look. If you can create a propulsion mechanism that is part of the roadway, you can create "trains" from cars that are spacially close but not mechanically linked. Then it becomes very efficient.  Also, if you exploit levitation to utilize the 3rd dimension, capacity of the road is increased dramatically.  --Tbeatty 21:33, 18 February 2007 (UTC)

astronomy question 1: Centauri
I read somewhere, probably on Wikipedia, that the ooort cloud probably ends about two lightyears from the sun, and that the nearest stars are about 4 lightyears away. Could we therefore assume that anything beyond the ooort cloud orbits the nearest star (Proxima centauri)? ANd if we can detect tiny rocks that far away, could we find planets orbiting nearby stars? How big would an object have to be for something to detect it four lightyears away? And could something be put halfway between two stars so that it doesn't move as there is equal gravity pulling it each way?Hidden secret 7 12:07, 18 February 2007 (UTC)
 * The Oort Cloud is largely hypothetical. Current models of the Solar System predict that it exists, and it is probably there, but we haven't actually seen it. Between us and Alpha Centauri, there is what is called the Interstellar Medium. It isn't much, only a few hydrogen atoms per several cubic meters of space. These things don't really orbit a star, because the force of gravity diminishes with distance, and the distances we are talking about are inconceivably huge. Like I said, we haven't really detected these rocks, but we can detect other planets. See Extrasolar planet for more information on how other planets are found, it is really interesting. As for an object between the two stars, I don't think it would do anything, because the forces of gravity would be so small at that distance. GhostPirate 12:29, 18 February 2007 (UTC)
 * Just as another thought, scientists have found 212 planets orbiting other stars. GhostPirate 12:30, 18 February 2007 (UTC)


 * Well, it's not so much that the forces are small - the tiniest of forces can still produce an orbit if there's nothing else around - it's just that anything else that happened to pass by would knock them clean off their orbits. That said, if we're considering just the isolated system of these two stars, then bear in mind that the gravitational forces from the Sun and proxima centauri are very different. Proxima centauri is only a tenth the mass of the Sun, so the Lagrange point inbetween them, where the forces balance, is closer to the other star. (In the same way that Venus is 'closer' to the Earth than it is to the Sun, but it definitely goes round the Sun!) (Oh, please note there isn't really a Lagrange point betwen them, because p.c. is not orbiting the Sun, but the mental image of the 'balance points' is quite illustrative.)
 * In reality, both the Sun, proxima centauri and all the other stars are moving around quite a lot, and so anything at that distance will almost cetainly have been perturbed by the cumulative effects of p.c. and other stars by now. There's also the difficulty of getting anything to form at that distance. If the solar system formed from the collapse of a molecular cloud, then all the mass ends up at the centre, and there's not much left to form planetesimals with beyond the Oort cloud. There might be a stable orbit there, but no way of filling it. Spiral Wave 13:56, 18 February 2007 (UTC)

astronomy question 2: Moons
Would it be possible for a moon to have objects orbiting it? How much would the planet near it affect these objects and what would they be called? Would it be possible for people to put something in orbit around our moon, for example if we decide to build houses there, or would it just orbit the earth? And would it be possible for someone to work out how far away it would have to be from the moons surface?Hidden secret 7 12:13, 18 February 2007 (UTC)


 * In theory yes, as long as the moon was large enough compared to its primary, far enough away from its primary and dense enough to have a Hill sphere that was significantly larger than the moon itself. In practice, our article on natural satellites says that there are no known examples of a "moon of a moon", and that such an arrangement would very likely be unstable. Gandalf61 12:31, 18 February 2007 (UTC)


 * Just did a quick calculation of the Hill radius of the Earth's Moon, and I make it about 61,500 km, or about one sixth of the distance from the Moon to the Earth. And although there are no known natural examples of moons of a moon, any spacecraft in a true lunar orbit is a man-made example. Spacecraft typically orbit the Moon at heights of between 200 and 2,000 km, so are well within the Moon's Hill sphere. Gandalf61 12:45, 18 February 2007 (UTC)


 * Yes, the Apollo missions, 8 and from 10 onwards, all did orbit the Moon, and the Lunar Orbiters probably make it about as clear as it gets! There are no natural moons of moons, although there are several asteroid moons, and most asteroids are smaller than most moons. As a slight mind-twister, to show how messy these cases can become, you might want to read Pluto's natural satellites. Nix and Hydra technically orbit both Pluto and its moon Charon, rather than just the dwarf planet, although Charon might yet be re-classified one day. Spiral Wave 14:13, 18 February 2007 (UTC)


 * If you're willing to broaden the question to "can a satellite have a satellite?", then you can consider the planets to be satellites of the Sun, and their respective moons to be satellites of satellites. --TotoBaggins 15:55, 18 February 2007 (UTC)


 * You should read Natural satellite - it's a great article. Certainly moons could in principle have moonlets of their own - but there are questions of long-term stability of such orbits which makes that rather unlikely - but not impossible.  (As others have said - we have made artificial satellites that orbit the moon for weeks at a time.  I don't know for sure but seems that with over 240 known moons, it's very likely that there is some tiny speck of matter is orbiting one of the moons out there that is just too small for us to detect.  If there was a rock that was (say) 10 meters across orbiting some remote moon of Saturn (for example), there is no way for us to have detected it. But if we did find such a thing - would we count that as a 'moon' officially?  It's hard to say.  The lower limit of size below which something is too small to count as a moon doesn't seem to be all that well defined - and in any case it's one of those arbitary limits that scientists hate to make.  Another interesting prospect is of objects that are orbiting an empty region of space with nothing whatever to orbit around!  This seems completely impossible at first sight - but there are several known examples of just this exact thing happening that are called 'Trojan moons'.   The places where this happens are called the 'Lagrange points' - they are places with the orbits of other moons where there is a point of stability in the gravitational field of moon and planet.  Weirder still, there are arguments in favor of saying that our Moon isn't a moon at all and that the Earth/Moon system should really be considered a 'binary planet' because the moon is so large and so close to the Earth.  The Pluto/Charon system is an even better candidate for that title because Pluto and Charon orbit each other (the center of mass of the pair lies betwen them rather than inside Pluto) - but since Pluto got demoted from a planet to an 'ice dwarf', the title 'binary planet' for the pair has not made it into the language of astronomers.  But there is scope in those kinds of systems for small 'moons' that orbit around the center of mass of the binary pair.  Yet weirder, some asteroids known to have tiny moons.  SteveBaker 18:46, 18 February 2007 (UTC)


 * Planetary formation may (or may not) provide a definitive theoretical answer (within the limitations of how well we understand the process) as to the maximum number of natural satellite hierarchies. Hypothetically, one could calculate how much matter gets ejected out of the star; what densities are necessary for accretion; how big the object would be; whether it would simply soak up all the remaining matter into its own body or allow for formation of a satellite; and then iterate the process for each sub-satellite system.  Strictly from empirical evidence of our own solar system, I would say you can have at most three levels (Sun -> Planet -> Moon or similar arrangements).  Nimur 19:32, 18 February 2007 (UTC)


 * Yeah - but there are other ways for small moonlets to arrive in orbit: They might be a 'captured' meteor - they might be chunks of the parent object that was chipped off and flung into orbit by a collision - there are all sorts of ways for these things to get where they are today. SteveBaker 01:46, 19 February 2007 (UTC)

astronomy question 3: Density
On earth heavy things fall, and inside the earth denser material such as metal is in the centre, whilst the air has floated to the top. Therefore in the entire solar system it would make sense that planets closer to the sun should be denser. tHe inner planets are mostly rocks and metal, whilst further out there are planets made of gas, but beyond these are other planets made of rock, ice, &c. How did it get out there? And some moons are made of materials nothing like thair planets, so where did they come from? The least dense material is hydrogen and helium, which is mostly in the sun, right in the middle. Shouldn't this have floated to the edge of the solar syatem long before the sun was even created? I would assume the pressure on the gasses could affect this, but right at the begining of the solar system there were no planets to create this pressure.Hidden secret 7 12:19, 18 February 2007 (UTC)
 * The Sun was formed when a huge molecular cloud collapsed down into a single space. Pressure is what stops the Sun getting any smaller than it is now, but it couldn't make the hydrogen drift away then any more than it can now. Gravity is simply too strong; it can't "float away". The cloud was also rotating, and as it collapsed it flattened out into a protoplanetary disc, with all the material that had too much angular momentum to fall straight to the middle.
 * If you drop something on Earth, it falls towards the centre because there's nothing to stop it. The International Space Station, however, is made of metal (and other stuff) but is clearly not dropping straight down. Nor is the Moon, which is rock. They are both in orbit around the Earth. Likewise, the planets formed from the large protoplanetary disc, the solar nebula, which was in orbit around the Sun, so they couldn't just 'fall' and separate out like a layer of oil on water. There is a gradient with more metals towards the centre and more ices at the extremeties, but it's not that sharp, and you can in principle find everything everywhere.
 * With that in mind, you're actually looking at the question backwards. It's not that there is rock out there, it's that there isn't any ice over here. Close to the Sun, all the ices - volatiles - were evaporated by the heat, and unable to be accreted into planetesimals. The protoplanetary disc had something called the snow line, between Mars and Jupiter, and beyond that point it's cold enough that the volatiles condense into solids. The amount of material available to accrete jumps up, so the planets grew bigger. There's actually much more rock in any of the four giant planets than there is in all the four inner planets put together; they have large solid cores under all that gas. But the rocks are 'diluted' by all the extra ices.
 * Also, the protoplanetary disc was an accretion disc, with new material being swept in from outside. So more rock and metals were continually being brought in to the inner system, while volatiles were being evaporated, which partially explains why the inner planets are metal-rich.
 * The hydrogen, helium etc is simply because those planets became massive enough to capture the gas in the disc too; the inner planets were also embedded in it, but they couldn't capture any. The ice giants, which have tiny atmospheres compared to Jupiter and Saturn, probably only got big enough to accrete gas after most of it had gone and only the ices, which are more massive and harder to photoevaporate, were left.
 * As for the moons, that's the same as above. They're metal, rock and ice, same as their parent planets' cores, that formed in the same regions and were captured by gravity. Some of them will also be Kuiper belt objects scattered inwards during the formation and evolution of the solar system, explaining slightly higher ice contents. Some moons will have formed from the smaller gas discs around each giant planet, leading to differentiation which may explain the variation among the galilean moons, for example. The rest of it is just down to pot luck. Spiral Wave 15:18, 18 February 2007 (UTC)


 * To answer the sun question, the sun, like most stars, start out as hydrogen, with traces of other heavier elements. As the sun ages, denser elements form. Hope this helps. A  stroHur  ricane  00  1 (Talk+Contribs+Ubx) 00:55, 20 February 2007 (UTC)

biochemistry-carbohydrates
Hi there. Please could you help me understand how to draw the strucure of different carbohydrates. I need to know how to structurally draw a hexose and a tetrose. I know the difference between the 2 is the number of carbons each one has, eg: hexose has 6 carbons.

Please show me the structural difference between the 2! Thank you very much.

Megan Megan Medina 15:14, 18 February 2007 (UTC)

glucose shows a hexose drawn different ways. hexose also shows one way to represent them.

There is an image of threose a tetrose here http://www.steve.gb.com/images/molecules/sugars/D-threose.png in both oen chain and ring form.

Searching for tetrose or hexose using an image search is probably the best way to get examples of the way they are drawn.87.102.9.240 15:32, 18 February 2007 (UTC)

If you want to know more about the way the structures are drawn 'flat' as they are at hexose you should look at Fischer projection87.102.9.240 15:33, 18 February 2007 (UTC)

Dominant?
Is polydactylism (more than 5 fingers per hand) dominant? I read that it was in a book but just wanted to check. Coolotter88 16:38, 18 February 2007 (UTC)


 * Please check the article before posting here. See Polydactyly (end of the first paragraph). Pro bug catcher (talk • contribs). 16:50, 18 February 2007 (UTC)

Only genetic polydactyly is, obviously non genetic versions of it can not be inherited directly

Difference between harmonics and overtones
ok in in simple 12th grde terms can anyone give me the difference between harmonics and overtones.i was reading abt different modes of tranverse vibrations on a stretched string and the textbook doestnt elaborate the difference.thanks in advance!!59.183.45.138 17:01, 18 February 2007 (UTC)


 * A harmonic is a vibrational mode at a frequency which is an integer multiple of the natural frequency. So if the natural frequency is 440 Hz, the first harmonic is 880 Hz, the second is 1320 Hz, etc. To picture this concept, draw two fixed points and try to connect them with a sinusoid. The fundamental is a half sine wave, the first harmonic is a full sine wave (the wavelength is the same as the distance between the ends), the second harmonic is 3/2 of a single wave. Overtones occur when a system has more than one natural frequency (as many systems do). The lowest one in frequency is the fundamental frequency, and the next highest natural frequency is the first overtone. These do not have to be integer multiples of one another. anonymous6494 17:28, 18 February 2007 (UTC)


 * The two terms, as usually used, mean the same thing. If there is any distinction it would be that harmonic is a more mathematical concept, of a tone or oscillation at a frequency that is an exact multiple of the fundamental, whereas overtone might be used more often in a more practical context of music to refer to an overtone that you get in practice even if its frequency is not exactly a multiple of the fundamental. For example, the article harmonic states that Overtones whose frequency is not an integer multiple of the fundamental are called inharmonic and are often perceived as unpleasant. Such an anharmonic overtone might occur if, say, your guitar string is corroded. -- mglg(talk) 20:57, 18 February 2007 (UTC)

Foot Fall Asleep
Hi all...

Often times when we sit in the same position.... our "foot falls asleep" I was wondering if wikipedia has any info on that. Like why that happens and the commonality of it, etc... Why does it hurt? Is there a way to fix it?

Thanks --Spundun 18:32, 18 February 2007 (UTC)


 * We were just talking about this a few days ago. Wikipedia does indeed have articles: see Paresthesia and Obdormition. —Steve Summit (talk) 18:38, 18 February 2007 (UTC)


 * We have an article on polyneuropathy but apparently not polyradiculoneuropathy. Why?  My best guess is that it is the multiple failure of nerves at a point near the spinal cord (radix=root).  Anybody actually know what this word is?  (Anyone know how it ranks in the list of long words? Nimur 19:40, 18 February 2007 (UTC)


 * Google turns up "Chronic Inflammatory Demyelinating Polyradiculoneuropathy." That one surely must rank highly in the list of outrageous medical conditions you can say you have.  It must be a great conversation starter. Nimur 19:43, 18 February 2007 (UTC)


 * Also, on the topic of obscure medical terminology, "idiopathic" sounds like it was invented by a disgruntled doctor or nosologist. Nimur 19:45, 18 February 2007 (UTC)


 * Or Robert J. Hanlon. —Steve Summit (talk) 22:04, 18 February 2007 (UTC)

alcohol question #1
why does drinking too much make u puke?
 * Note: please sign your posts with --~ ; thanks.
 * Your body treats a large amount of alcohol as a poison. A common reaction to many kinds of poison is to vomit, so as to prevent absorbing any more of it that's in your stomach. --TotoBaggins 20:54, 18 February 2007 (UTC)


 * Alcohol is poison. In small amounts your body can handle it. In larger amounts, your body will do what is GOOD for you and expel as much of the poison as it can. 202.168.50.40 22:08, 18 February 2007 (UTC)


 * More specifically, ethyl alcohol is an organic solvent, and just like the other alcohols, it attacks your liver. -- mattb

alcohol question #2
can drinking 1 bottle of beer (341mL or 355mL) or 1 glass of wine (200-2500mL) raise your blood alcohol over the U.S. legal limit for driving (0.08%)?
 * It depends on the drinker's weight. My wife weighs 90 lbs, and while I don't know if she'd be over the legal limit, she certainly doesn't seem to be in condition to drive after a full glass of wine. --TotoBaggins 20:52, 18 February 2007 (UTC)


 * Err on the side of caution and don't drive. Nimur 20:55, 18 February 2007 (UTC)


 * Your upper limit of 2500ml would certainly do it. Fatally, most likely. That's 1 big glass. Edison 20:25, 19 February 2007 (UTC)

alcohol question #3
does wine need to be refrigerated after opening? if so, how long before it spoils? what about whisky? vodka? champaign? can any of these be kept at room temperature for extended periods (a month to a year or more) in a container that is opened and closed once in a while until the container is finished? what about beer? (i know beer tastes like crap if its not chilled but im just curious)
 * Beer and wine need to be refrigerated after opening. Wine will be OK for a day or two after opening.  Beer and champagne will be pleasant for an even shorter period after opening, due to losing their carbonation.  Hard liquors like whiskey and vodka have enough alcohol that they preserve themselves, so can be opened and closed and kept at room temperature more or less indefinitely.  Some liqueurs and things will be somewhere in between.  --TotoBaggins 20:59, 18 February 2007 (UTC)


 * I've been told that if it burns it is OK to keep at room temperature. --Kainaw (talk) 00:44, 19 February 2007 (UTC)
 * Have you heard the wife's tale about keeping champagne in the fridge with a silver spoon in the neck in order to keep its taste? The silver spoon does nothing but keeping the champagne open in the fridge actually keeps it bubbly and helps to keep it tasting better. Putting a stop on the top and leaving it in the warm is the worst thing you can do. 213.48.15.234 12:08, 19 February 2007 (UTC)
 * My wife also puts the handle of a teaspoon down into the neck of the bottle to keep the Champaign bubbly overnight - and as a scientific sort of person, I thought this had to be bogus. I mean, how could that possibly help?  But 'The Mythbusters' TV show did a reasonably careful study of half a dozen ways to store the stuff - and to my amazement, they showed that putting a spoon into the neck of the bottle not only doesn't help - but actually makes the champaign lose its fizz faster than an open bottle?!?  Nobody really seems to understand why. It would make a good research topic for a first year college student. SteveBaker 18:11, 19 February 2007 (UTC)


 * More nucleation points means faster loss of carbonation. The spoon provides more nucleation points.


 * Atlant 18:18, 20 February 2007 (UTC)

alcohol question #4
why does the same amount of alcohol make an ocasional drinker more tipsy than a heavy drinker? doesnt this make the set legal limit kind of stupid? isnt there a better way to objectively measure "drunkenness" than %alcohol in the blood?
 * I believe your statement is a common myth. "Holding your liquor" doesn't have a scientific basis, as far as I know.  Weight, stomach contents, biochemistry- these certainly have an effect on intoxication.  I don't believe frequency of consumption actually does.  As far as the "objectivity" - the purpose of blood alcohol content is to be objective and quantitative.  This avoids "debating" whether somebody is intoxicated - it is simply a number, and if it is above a certain limit, then there are legal repercussions. Nimur 21:02, 18 February 2007 (UTC)


 * Another way to look at it: I know a guy who drinks all day every day - even when driving. He says he's been drinking beer all day every day since he was 13, so it has no affect on him - other than the fact that he is slow, dumb, clubsy, sleepy... basically always drunk.  If he sobered up, he would likely be a completely different person.  But, since he is always a bit drunk it appears that he can drink a lot without getting drunk. --Kainaw (talk) 00:43, 19 February 2007 (UTC)

Alcohol affects the neurotransmitters in the brain. If you are sensitive to alcohol, even a tiny amount will knock you over. If you keep drinking a lot, the brain compensates and doesn't react that much. As well, the livers of drinkers go hyperactive, and burn it up faster. --Zeizmic 12:54, 19 February 2007 (UTC)


 * The implication is in the other way I think. Obviously those people that get sick from drinking the tiniest bit of alcohol will rarely become a heavy drinker.  &#x2013; b_jonas 17:33, 19 February 2007 (UTC)

alcohol question #5
are beer and champaign intentionally carbonated, or does the CO2 form by itself during the fermentation/brewing process?
 * Mostly it is natural. See fermentation or beer or champagne. Nimur 20:59, 18 February 2007 (UTC)


 * [edit conflict]
 * Well, certainly the carbonation is intentional in any case! According to our articles on beer and champagne, the carbonation is a result of a secondary fermentation, involving the addition of sugar, and perhaps extra yeast, as a last state of production.  This natural carbonation is used in all champagnes and some beers. —Steve Summit (talk) 20:59, 18 February 2007 (UTC)


 * Most beers have carbonation added, so they end up fizzier than the natural carbonation produced by fermentation. Beers that are bottle or cask conditioned would be an exception.  Friday (talk) 17:39, 19 February 2007 (UTC)

last but not least, alcohol question #6
can pure ethanol be added to juice to make alcoholic drinks? what about adding vodka to juice (say.. orange, apple or fruit punch)?
 * In theory, yes. In practice, you should be aware of how (im)pure your ethanol actually is.  You should also consider how concentrated your final product is so you don't kill yourself.  See effects of alcohol on the body.  Err on the side of caution. Nimur 20:57, 18 February 2007 (UTC)

Pure ethanol is (drinking) alcohol. However the devil is in the details which in this case is the way ethanol is made. Industrial ethanol production creates ethanol with high impurities (ie. 97% ethanol and 3% impurities). These impurities can be extremely damaging to the human body. AS SUCH ethanol not created for human consumption should NEVER be added to drinks for humans. 202.168.50.40 22:04, 18 February 2007 (UTC)
 * As to the second part of your question about adding vodka to juice, that's very common. Oange juice with vodka even has it's own name, it's called a screwdriver (cocktail). I like vodka with cranberry personally. Vespine 22:55, 18 February 2007 (UTC)


 * Well, the ethanol that's made for drinking isn't strictly "pure", either -- in fact it's less pure than industrial ethanol! As the Ethanol article explains, conventional distillation cannot produce alcohol more concentrated than 95.6%; the other 4.4% is water.  The impurities in industrial ethanol are residues of the drying agents (such as benzene) which are used to improve the alcohol purity, e.g. up to 97% or more.  (But yes, those drying agents are generally toxic, and thus industrial alcohol should never be used for human consumption.) —Steve Summit (talk) 22:19, 18 February 2007 (UTC)


 * The impurities in alcohol made for human consumption are very different in nature from the ones present in industrial ethanol which are known to cause a range of nasty conditions - notably blindness. Don't even think of using industrial ethanol. SteveBaker 01:40, 19 February 2007 (UTC)


 * See Lie to children. 202.168.50.40 23:39, 18 February 2007 (UTC)


 * I have never seen a drinking alcohol that didn't have either an ABV or Proof marked on it. For liquers (as opposed to wines and beers), I only see Proof, which is pretty much just double the alchohol by volume.  190 proof is the "pure alcohol", and is rather easy to find.  We had many brands of 190 proof grain alcohol when I was in college.  Standard practice for drinking it was to mix it with a clear soda (Sprite or 7-Up) and fruit juice. --Kainaw (talk) 00:40, 19 February 2007 (UTC)
 * Everclear, etc. are not universally legal. Rmhermen 03:02, 20 February 2007 (UTC)

Marsupial genitalia
Does a marsupial have a clitoris? Wiwaxia 21:39, 18 February 2007 (UTC)
 * Googling marsupial + clitoris suggests that female marsupials do have clitorides. ---Sluzzelin 22:36, 18 February 2007 (UTC)
 * "JSTOR: Gonadal Activity in the Marsupial Mouse, Antechinus bellus ...The reproductive biology of these marsupial mice is currently receiving ... was large and bordered by tumescent tissue, and the clitoris was prominent." Sure sounds like it! Thanks! Wiwaxia 23:00, 18 February 2007 (UTC)


 * Hyenas have huuuge ones! --Sonjaaa 07:41, 19 February 2007 (UTC)

Herring gull getting raped?
Just browsing the gull videos on YouTube when I discovered this video, which appears to show a herring gull being raped (by another herring gull, not a human!) - I find the last few seconds, showing the victim sprawled out on the rocks particularly harrowing.--Kurt Shaped Box 23:46, 21 February 2007 (UTC)

I know that some creatures have been known to rape others of their own kind (mallards for example) but I was not aware that gulls were one of those species. Has anyone here ever seen/read/heard about gulls doing this? I've spent a lot of time observing the gulls over the years and I have never noticed any behaviour that I could obviously interpret as 'sexual violence'. Without trying to anthropomorphise things too much - if you guys had been there to see that, would you see it as your moral duty to step in to stop it, if possible? --Kurt Shaped Box 00:01, 18 February 2007 (UTC)


 * Say you're on safari in Africa and see a lion about to spring on its unsuspecting prey. Is it moral to shout and alert the animal to its danger? Clarityfiend 00:50, 18 February 2007 (UTC)


 * Good question. I don't honestly know what I'd do in that situation. I have saved small creatures from domestic cats before because it seemed like the 'right thing to do' at the time. I don't think my conscience would allow me to stand by whilst a violent rape occurred. --Kurt Shaped Box 01:03, 18 February 2007 (UTC)


 * I'm inclined to think that it's just part and parcel of Mother Nature, neither right nor wrong in itself. Based on that premise, I don't see that it's moral to interfere, no matter how right it feels. (Unless of course the gull is wearing a mask.) Clarityfiend 02:20, 18 February 2007 (UTC)


 * Same here, and I also wouldn't want to jump to the "human" rape. If the birds are in season, aren't they all fair-game? Are there actual life partners? [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 07:37, 18 February 2007 (UTC)
 * As long as we're getting philosophical, I would advise against invoking natural utilitarianism; the idea that there is a certain "natural" order of the universe which should be respected leads to particularly brutal and violent conclusions, like racial survival struggles, moral rape (as mentioned), cannabalism. Morality is a creation of human nature, it isn't "natural" - I say we should keep it that way.    --Bmk 08:06, 18 February 2007 (UTC)


 * AFAIK, many gull species pair up for a long time, if not for life. From the vid, it's clear that the female gull (okay, it may be a male - it's hard to tell) is in distress (looks like the rapist nearly drowns it). Nature is red in tooth and claw but I (as part of nature myself) hate to see unnecessary suffering and sheer cruelty. --Kurt Shaped Box 08:12, 18 February 2007 (UTC)


 * Personal observation: My parents keep chickens. I think all the sexual encounters in the chicken yard can be described as rape and sometimes gang rape.  I see no moral duty to try to prevent this, sure you may intervene if you happen to notice one of the hens getting harrassed excessively. You can't be out there 24/7 for the sake of moral duty, so why even try to enforce your own morality. Diletante 18:48, 20 February 2007 (UTC)


 * Didn't you see how the rapist nearly drowned the victim in that video? That's just wrong as far as I'm concerned. I mean, what is the point of that? I know that animals sometimes rape other animals so that they don't have to bother will all that 'courtship' hassle - but what good does it do for the rapist's genes if the rapeee is dead? --Kurt Shaped Box 23:46, 21 February 2007 (UTC)


 * More importantly, the question is, is it rape or instinct? I think it is likely the one herring's severe distress came from nearly drowning, not from the intercourse. Also, as a "dumb" herring, the other was not aware that it was killing the first; it simply wanted to complete the mating process. The non-consensual behaviour in the first few seconds, before the first one went into the water, is fairly common among many species, including birds.

Two questions that just popped up in my head
First, and I don't really have a better way of wording this, is farting good for you? When you hold a lot in, it doesn't feel very good, and when you fart a lot, it feels, for lack of a better word, fantastic. Is it as good for you as it feels to rip a big one? Is holding many in bad? Second, why do I love the smell of burnt meat? In human evolutionary history, wasn't the use of fire to cook food a late development? So why would I have such a strong physical reaction to the smell of cooked meat? I can smell it from a great distance, and can tell what type of meat is cooking, and I crave it all. Why? Thanks, 70.108.199.130 06:20, 18 February 2007 (UTC)


 * The flatulence article will probably answer your first question. Flatulence is a natural thing and there is no physiological reason why you should hold it in. As to your meat question. I would say that it is in fact a evolutionary thing. Cooked meat is less likely to carry dangerous bacteria, and thus evolution has taught our bodies to crave cooked meat. - Akamad 07:06, 18 February 2007 (UTC)


 * But how could we evolve to like cooked meat back in the days when there was no cooked meat around? A.Z. 23:11, 18 February 2007 (UTC)
 * If God had meant us not to eat animals, why are they made out of meat? Was a joke that I thought was pretty funny:) But seriously, taste evolution need not be a process that took millions of years, there were bacteria that evolved to eat byproducts of nylon production in just a few decades. Cooked meat keeps a lot longer and would make you sick a LOT less then anything but the freshest raw meat, it was obviously a great advantage to cook meat before eating it, so we developed a 'taste' for it.Vespine 00:34, 19 February 2007 (UTC)
 * I get your theory, but let me understand it better. You are saying the first man which cooked an animal didn´t like the taste of it and then, after a lot of generations of humans dying from eating bacteria in raw meat and yet cooking some meat once in a while (for some reason), the ones which had some mutation which made them like cooked meat were selected and survived and those mutations became spread among all humans? Is it what you say? A.Z. 03:55, 19 February 2007 (UTC)

Or it might not have been a mutation like that, everyone could have already liked cooked meat, but not known as they had never tried it before:)


 * Perhaps your liking of the smell of meat is a result of the fact that in your lifetime, you've eaten meat regularly and learned to enjoy it. It smells good to you, so you respond by feeling hungry. It need not be a genetic trait...I think the word is conditioning? I have a strong positive reaction to the smell of baking cookies, but I don't think that comes from a genetic mutation. Someone from a culture that doesn't have cookies might not like the smell. --Grace 01:09, 22 February 2007 (UTC)

yoghurts left out of fridge for 24 hours
can I still eat them?


 * I would. But I have a strong stomach. Nimur 20:35, 18 February 2007 (UTC)
 * If they were unopened I would too - I'd put them back in the fridge so they were cool again - that's how I've learnt to like them.87.102.9.240 20:43, 18 February 2007 (UTC)
 * Well, check for any traces of mould, or any foul or unusual smell. If there are any, then best to throw it out. A  stroHur  ricane  00  1 (Talk+Contribs+Ubx)

I put them back in the fridge and then ate them, they seem all right but taste a bit odd:) What actually was the point of putting them back as all the bacteria will have already multiplied:?


 * It was, I think, to cool them down so that they taste nicer. :) D  aniel  (‽) 16:24, 21 February 2007 (UTC)


 * Yoghurt is made of milk+bacteria. Since those forms of bacteria produce acid which kills other organisms, making yoghurt is a way of preserving milk without refrigeration.   On the other hand, if your yogurt was contaminated by dirty spoons, it might grow some salmonella and lead to food poisoning.--Wjbeaty 04:02, 23 February 2007 (UTC)

= February 19 =

Global Warming
It has been determined how much more ppm carbon dioxide has been added to the atmosphere. How much more oxygen would there be in he atmosphere if we had not burned fossil fuels?


 * I don't know the answer - but it's not a particularly relevent question - global warming is nothing to do with running low on oxygen - it's that we have too much CO2. If even 0.5% of the air was CO2, humans would die from breathing it.  But the oxygen needed to make that much CO2 is a very tiny fraction of the oxygen available in the air - not even enough to be noticable. SteveBaker 00:31, 19 February 2007 (UTC)


 * While 0.5% CO2 sounds like a miniscule amount, it is more than 10 times the current concentration, which is 0.04%. There are no current threats to tne environment that will make CO2 concentrations multiple 10 times very quickly. --Kainaw (talk) 00:35, 19 February 2007 (UTC)
 * Carbon dioxide content in fresh air varies and is between 0.03% (300 ppm) to 0.06% (600 ppm) The earth mean is about 420 ppm. Also, we don't know for sure how much carbon dioxide has been "added" to the atmosphere—there are many carbon cycles and we hardly have a grasp of them if at all. We don't know for sure how much oxygen there would be if we never burned anything— there are far far far too many factors that determine gas concentrations in the atmosphere. [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 00:41, 19 February 2007 (UTC)


 * You might be interested in the very tiny graph inside the upper-left graph at http://www.grida.no/climate/ipcc_tar/wg1/fig3-2.htm (direct link to picture). (I'd expect an updated version of that graph when the full IPCC 2007 report comes out in May, I think.)  It shows that oxygen levels have dropped about 10 ppm - whether that means we consumed the oxygen has to be determined.  Also, 10 ppm is tiny compared to the total oxygen in the air, so we're not in danger of running out of oxygen to breathe.
 * Also, to clarity, whether or not we added CO2 has been determined, just not exactly how much (it may be more or less than the amount of measured increase, due to either positive feedback or negative feedback cycles). —AySz88\ ^ - ^ 04:50, 19 February 2007 (UTC)
 * See Carbon cycle. There are lots of sources and sinks for carbon dioxide.  --Tbeatty 05:19, 19 February 2007 (UTC)
 * To quote me from before, on September 26th:
 * The carbon cycles can be described as follows:
 * Break the earth into carbon reservoirs. i.e. atmosphere, hydrosphere, biosphere, geosphere, carbonate rocks, fossil fuel deposits, marine sediments—you can go into as much detail as you want.
 * For n reservoirs, there are n-1 carbon fluxes between the selected reservoir and the other reservoirs, combinatorially, (n2-2n+1) total fluxes.
 * Measure the n2-2n+1 fluxes, and analyze their chemistries (organic, inorganic, solid, liquid, gas—as much detail as you want)
 * Calculate residence times T for carbon in each reservoir, the mean time an atom of carbon resides in the reservoir. Time is reservoir content C (assumed to be constant, although it is not) over by the sum of rates at which C is added, or the sum of rates at which C is subtracted, to or from other reservoirs. One must be consistent in the use of the reservoirs one defines (Kevin E. Trenberth's research at NCAR is a good example of how not to do this—atmospheric reservoir suddenly turns into all "mobile" C on the planet when calculating T of fossil fuel derived CO2 in the atmosphere)
 * [...] most reservoir and flux data are order of magnitude estimates.
 * "Lots" is a nice word for this! [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 07:51, 19 February 2007 (UTC)
 * Well, to answer the oxygen question, the Earth is depleting from oxygen in some areas. Deforestation also reduces the amount of oxygen, but more carbon dioxide can encourage more trees, since there should still be enough oxygen. Hope this helps. A  stroHur  ricane  00  1 (Talk+Contribs+Ubx) 00:33, 20 February 2007 (UTC)

Toes like fingers medical condition name
What is the name of the medical condition in which the toes are separated through three joins like the fingers? I was talking to a football player from Southern Mississippi who played with Brett Farve and he said that he believes Brett's powerful balance comes from his "weird finger toes". As a trick, he'd curl his toes around a baseball and throw it. So, I was wondering what this condition is called. --Kainaw (talk) 00:56, 19 February 2007 (UTC)
 * Hyperphalangy GB 02:10, 19 February 2007 (UTC)

Chocolate through the mail
What would be the effects on a bar of chocolate being sent through the mail in a small package? Would the US postal service be likely to melt it partially or fully? [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 03:44, 19 February 2007 (UTC)


 * I´d say it depends on various factors which may or may not be present. Why don´t you send a bar of chocolate through the mail and see what happens? A.Z. 04:12, 19 February 2007 (UTC)


 * It's only one data point, but I sent several bars of chocolate through the U.S. Mail as a Christmas present and I'm told they got through just fine. —Steve Summit (talk) 04:55, 19 February 2007 (UTC)


 * Because they don't sell Milka anywhere in the U.S. that I can find, I have to order it from Germany. I would order from Norway (tastes better, but far more expensive).  Each case always arrives just fine. --Kainaw (talk) 05:09, 19 February 2007 (UTC)
 * Ah, thank you :) I want to send some chocolate to one of my friends in Illinois, I think it will get there just fine. I knew Godiva (chocolatier) sent chocolate through the mail but wasn't sure if they did anything special in packaging to prevent melting. [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 07:54, 19 February 2007 (UTC)


 * I'd worry more in the summertime, of course. —Steve Summit (talk) 13:33, 19 February 2007 (UTC)


 * I'm pretty sure that most food sent through a catalog comes through fine. I know that Williams-Sonoma sends sausages through the mail... - AMP&#39;d 13:57, 19 February 2007 (UTC)


 * Some mail order candy companies have disclaimers about sending chocolate through the mail in warm months, but other than that, chocolate gets through generally unharmed. Corvus cornix 19:34, 19 February 2007 (UTC)

bath to completely relax muscles?
what's the best thing I can put in a hot bath to relieve muscle tension from sendentarism? are there salts or herbs or something that help make muscles relax completely?--Sonjaaa 07:39, 19 February 2007 (UTC)
 * I'm not sure that the chemicals actually directly "relieve muscle tension" but more, relax your mind, which lets you ease. [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 07:56, 19 February 2007 (UTC)

Try Epson Salt. PitchBlack 17:09, 19 February 2007 (UTC)
 * Yeah, there's some evidence that Epsom salt functions by replenishing lost magnesium ions. There is some information  here and  here.  Also, try stretching when your muscles are "warmed-up".  Good luck! --Cody.Pope 18:08, 19 February 2007 (UTC)

Wavelength
Which has the longest wavelength of the following?? a) radio waves b) sound waves c) X-rays d) infrared rays —Preceding unsigned comment added by Pujhitha (talk • contribs)

Try looking at Electromagnetic Spectrum MHDIV ɪŋglɪʃnɜː(r)d  ( Suggestion? | wanna chat? ) 11:56, 19 February 2007 (UTC)


 * You will also need to look at sound, and possibly infrasound and ultrasound, to get your answer. Spiral Wave 12:25, 19 February 2007 (UTC)


 * Seems to me this is an insufficiently precise question, as two of these categories of waves have a significant overlap in wavelengths. Gandalf61 13:23, 19 February 2007 (UTC)

The answer is radio...by far. AM commercial radio has wavelengths of hundreds of meters. The US and Russian navies use 'ELF' radio waves with wavelengths of thousands of kilometers for communicating with their submarines at sea. Sound waves in the range of human hearing (excluding ultrasound and infrasound) are a few meters so they are longer than some of the highest frequency radio waves but shorter than others, X-rays are down in the picometer range - very short wavelengths. Infrared is micrometers. There are longer wavelengths in 'infrasound' - but then you start to get into things like ocean waves and seismic wave (which are really "sound" at lower frequencies than our ears can pick up) SteveBaker 16:01, 19 February 2007 (UTC)


 * Well, sound waves can have arbitrarily long wavelengths, so your question doesn't really have an answer.  --bmk
 * I guess electromagnetic waves can be arbitarily long too. Pick up a magnet and wave it around really slowly and you'll end up with electromagnetic waves ("radio") that could be millions of kilometers long. But long wavelength "sound" is really just bulk motion - you don't get the perception of sound.  When you see a pendulum swinging once a second, you don't think in terms of 1Hz "sound".  When a hurricaine spins around once per day or so, we don't think of it making a sound at a frequency of a few microhertz.  So, like so many of these things, it all comes down to an arbitary "what is it called" question rather than any kind of scientific "what is it really" kind of a question.  But the answer I feel happiest with is that if we are talking sound that is audible to humans - then the answer is definitely radio. SteveBaker 05:15, 20 February 2007 (UTC)

My OJ froze!
I had a carton of orange juice in my sub-zero Celcius fridge. It's alright, really - I just place milk and OJ on the door shelf of the fridge, and this way they never really freeze. I think OJ and milk also only freeze at slightly less than -0, like -0.8 or something like it. Anyway, I forgot about the door-shelf, and put the OJ in the main compartment. Is it safe for me to drink the OJ when it in the future... uh, thaws? 81.93.102.185 17:40, 19 February 2007 (UTC)


 * Yeah - it's fine. Lots of people sell frozen OJ.   Make sure it's all defrosted though - if there is a lump of ice in the middle and you pour some of the liquid out, it'll be really concentrated - but then when the rest of it melts, you'll have weak-tasting OJ. SteveBaker 17:56, 19 February 2007 (UTC)

No its not safe for you send it to me! nah jk. anyways thaw it if you cant wait but dont forget to shake it so that the flavor returns to normal. Maverick423 19:01, 19 February 2007 (UTC)


 * Indeed it is safe. According to the movie trading places they even trade frozen orange juice on the Commodity markets. (Update): See New_York_Board_of_Trade ny156uk 23:33, 19 February 2007 (UTC)


 * From the label of some random orange juice on my desk - "Keep refrigerated. Once opened, consume within 2 days. Freezable. If freezing, freeze on the day of purchase, and consume within 1 month." Frozen orange juice makes good ice lollies too. --h2g2bob 14:00, 20 February 2007 (UTC)

Beetle Identification
I am trying to identify a beetle that has invaded my yard. It looks identical to the firefly but does not have a luminous abdomen. I am talking thousands.

a picture would be nice to help you out Maverick423 18:51, 19 February 2007 (UTC)
 * Note to original poster: please sign your posts with --~
 * Posting a picture to whatsthatbug.com might be more successful than posting here. --TotoBaggins 18:59, 19 February 2007 (UTC)


 * Could well be a firefly: "Many fireflies do not produce light". --Shantavira 08:18, 20 February 2007 (UTC)

venus flytrap
hi i got a venus flytrap the other day but since its winter i cant got out side and catch bugs for it.So i was wundering if there are any other thing i could feed it besides bugs that i mite find in my house such as some sort of meat product or some thing like that? Thanks alot 22:10, 19 February 2007 (UTC)
 * I personally love this thing we got going here, it like this big collection of interesting articles, and they can be searched for, sort of like your iPod. Click on this link Venus Flytrap.  --Zeizmic 22:31, 19 February 2007 (UTC)

as a former owner of a venus fly trap i can suggest that you go to a pet shop and buy those really tiny crickets. make sure that what you feed it is less then 1/3rd the size of the leaf if not then cut the cricket or food source in half with a surgical knife or blade. Remember never feed the traps anything bigger then 1/3rd the leaf size they cant handle it. it might be icky having to cut the bugs but hey if you truly love them you would do it right? my traps have already broken the 3 inch leaf mark =D they are getting quite big. I wish you luck and if you need any more help you can check the article that zeizmic has for you up there or you can also ask me =)Maverick423 22:43, 19 February 2007 (UTC)


 * I think you'll find ground beef is another Venus Flytrap taste treat. In all honesty, I don't think they're too picky ;-). Well, except maybe for this one: Tim Reid.


 * Atlant 18:32, 20 February 2007 (UTC)

Scientific Thoery
Hi I was wondering if someone could tell me what the theory that attempts to explain how populations change over time is. Brittney H. —The preceding unsigned comment was added by 72.191.106.131 (talk) 23:12, 19 February 2007 (UTC).


 * "The" theory? There's a penultimate theory that describes how "populations" change?  Could you be more specific?  Your question as stated could have anything to do with subjects from anthropology to mathematics to evolutionary biology... -- mattb


 * The study of real human population change is a very complex matter - too many factors interacting in too many ways most of which are poorly understood. You can have a nice prediction of population growth - then have some random element like a poor choice of political leader causing a massive war with population shrinkage - followed by a 'baby boom' nine months after the war ends.  There have even been recorded cases of small, localised baby booms happening exactly nine months after a power outage.  So imagining you could find anything other than the most simplistic model is just ridiculous.  However, if you are looking for a simplified model, a very popular demonstration is called 'Foxes and Rabbits' - and it's interesting because it can show predictable behavior or random chaotic behavior depending on the initial conditions that you choose.  There are a bazillion online descriptions of it - and doing a Google search will probably be the most productive way to find out more.  But here  is one reasonable description of this classic thought experiment. SteveBaker 03:41, 20 February 2007 (UTC)


 * Wait twenty or thirty thousand years for Hari Seldon to devise the theory of psychohistory. &#x2013; b_jonas 14:01, 21 February 2007 (UTC)

How cold fire can be?
How cold can fire be? What kind of fire is the coldest? What stuff I have to burn to have cold flame?

I am interested in this because I wonder what some will o' the wisps might be, and I would like to make a will o' wisp by my own. Some will o' wisps are propably not fire, but some are told to be like small blue or green flame close to surface. People sometimes see those at a swamp nearby, but I haven't seen such yet. Those never cause forest fires so they must be cold. That kind of will o' wisp might be explained by burning of some stuff that is coming from ground. But what stuff makes cold blue peaceful flame? Methane just blows up. Nitsimagoi 23:20, 19 February 2007 (UTC)


 * I think those come about from methane production from rotting vegetation under the marsh which is somehow ignited on the surface of the water with each bubble of gas producing a brief pale blue flame. The flames certainly produce heat - but I imagine the reason they don't cause forest fires is that it's really, really hard to set light to a swamp because everything is totally soaked in water!  So - returning to the original question - how cold could a flame be...hmmm...tricky.  Well, I guess what's going on is that rapid oxidisation of the fuel is causing ionisation of the resulting gasses - which makes them glow.  So there has to be enough energy in the flame to cause ionisation - or else no flame.  Oxidisation without a flame isn't what we'd call "fire" - it's more like "rusting" or "corrosion".  So I think the answer is that you can't have cold flames because you need a certain minimum amount of heat to actually cause a flame.  I have no clue as to what temperature that might be - it's certainly under 400 degrees C...but how much less, I don't know. SteveBaker 04:05, 20 February 2007 (UTC)
 * Here's an interesting discussion about this topic. DMacks 04:11, 20 February 2007 (UTC)
 * Yep - seems to agree with what I said - except they put the lower limit on temperature at 425C - my mental arithmetic put the answer below 400C based on black-body assumptions and the range of wavelengths for visible light. SteveBaker 04:58, 20 February 2007 (UTC)
 * I dont believe that coldest possible flame is 225c. I have touched flame that was not hot. 193.167.45.242 14:22, 20 February 2007 (UTC)
 * Also, blue flames are the hotest, not the coolest--Honeymane Heghlu meH QaQ jajvam 04:21, 20 February 2007 (UTC)
 * Yes - just take a look at the flame you get from a welding torch or something - compared to (say) a candle. SteveBaker 04:58, 20 February 2007 (UTC)

Color is not the best way to determine temperature of the flame. See flame test for some chemical causes for colors which have nothing to do with the temperature. Also, see Fahrenheit 451 for the the classic literary work - a reference to the temperature at which paper burns. That's an easy way to remember ballpark figures for fire. Nimur 01:21, 21 February 2007 (UTC)

y wont my venus flytrap eat?
i got a venus flytrap the other day so we went and bought some of those small crikets at a pet store. I put a plastic see throught cup over the flytrap (cup had a hole in the top) so that i could just leave the crikets in there and they wouldnt get out. but its been a few day now and it still hasnt eaten the crikets. y hasnt it eaten any of the crikets yet? thanks alot 23:54, 19 February 2007 (UTC)


 * I learn from reading our venus flytrap article that the plants don't eat very much -- the article says "the trap rarely catches more than three insects in its lifetime.". Remember, they can't hunt anything down; they have to wait for a live insect to land on one of their traps.  So maybe none of the crickets has happened to do that yet.  Also, do we know for sure that they eat crickets? I think I remember reading that the traps are scented with something that smells sort of like rotting meat -- which is of course attractive to flies.  But it might not be attractive to crickets. —Steve Summit (talk) 00:21, 20 February 2007 (UTC)

i know but wat i mean is that they wont close even if i rub the crikets on the trap or even if i rub the trap/triger hairs


 * Those hairs are delicate and work in a particular way. (Read the venus flytrap article for an explanation.)  They're designed not to be triggered inadvertently, that is, not by raindrops, and probably not by clumsy humans with well-meaning but unnatural offers of food, either.  I'd caution you against rubbing those hairs at all -- I suspect it's quite possible to damage them such that they'll never work.


 * Even though we all know how venus flytraps are supposed to work, and about the only reason for keeping them as pets houseplants is to watch them do it, it can be very frustrating to actually see them do it. (The one I had when I was a kid never did anything, either.) —Steve Summit (talk) 00:49, 20 February 2007 (UTC)

is it possible that they wont eat if thay wernt hungy or sumthin like that lol01:00, 20 February 2007 (UTC)


 * Bear in mind that these plants only need meat because they normally inhabit very poor soil. If they have good soil, they won't need to catch prey. Crickets are far too large and tough. As explained in the article, they eat small spiders and flies.--Shantavira 08:31, 20 February 2007 (UTC)

if you really want your plant to eat or are afraid it will die if it doesnt (which wont happen as long as you got the right soil and moisture) then kill a cricket make sure its not any bigger then 1/3 the size of the leaf (trap) and place it gently on the middle. with a peice of paper rub the hairs in the trap softly untill it closes. you might need 2 peices of paper to touch 2 hairs (which is why the plant is triggred) and make it shut. AVOID TEASING THE PLANT! do not make the traps close without food in it as they lose many fluids and nutrients in doing so! Maverick423 14:31, 20 February 2007 (UTC)

Did I got AIDS,and what to do??
I just had oral sex with a prostitute.I know it is very dumb thing to do,but I havent used condom,since she told me HIV can not be transmited through oral sex.What are the chances of me getting it from her? And is it true that Post-exposure prophylaxis can help??? ANd one more question,how can I check myself in London,because Im just here for 4 weeks,and I dont know where should I go,but it is very,very important,since I understand PEP can only help if it is being taken hours after getting the virus.So what are your advice,and please answer this honestly cause I am really worried,Im only 18 years old and I really dont wanna get aids and shit,so if is it possible that I got it through oral sex and what should I do?? Thank you


 * We can't really give you medical advice. But yes, oral sex can transmit the disease. I'm not so sure about where you can go, but you should definitely check it with a doctor. &mdash; Kieff | Talk 04:28, 19 February 2007 (UTC)
 * As the above states, definitely can't give you medical advice here, but I can tell you that Aids isn't the only thing you need to worry about, there are a whole list of sexually transmitted diseases which you have just potentially exposed yourself to. Statistically there probably isn't a very high chance a prostitute has Aids, maybe higher then the average "non prostitute", but I guatantee not as high as say hepatitis or herpes. The chance you caught something is still probably quite small but you have definitely put yourself into the risk group. Go see a doctor. Vespine 04:43, 19 February 2007 (UTC)
 * That may not be the case, depending on what type of prostitute (escort vs. street prostitute) he picked up. I worked in Vancouver's downtown eastside about 15 years ago (as a counsellor). Most of the street prostitutes were HIV positive. According to records, at least 20 of the victims alleged to be victims of Pickton were supposedly HIV positive. 20 out of approx. 49 is not a tiny percentage. -- Charlene 15:58, 22 February 2007 (UTC)

I have just called a free aids information number and they have told me that I should go to the hospital first thing in the morning and then recive Post-exposure prophylaxis.But they also say that aids test can not be done in less then 13 weeks after getting it.So is it a smart thing to go to hospital,even though it is possible that i havent got HIV at all?? And how do you mean that it is not likely that prostitute have aids,isnt it the most likely thing in the world?? I just hope that I got hepatitis or herpes,if that is a so I will be the happiest man in the world,cause it is nothing compared to aids


 * You should definitely go to the hospital. The doctors and nurses there will be much greater help than anyone on this reference desk. - Akamad 05:56, 19 February 2007 (UTC)


 * Though I have no statistics to back this up, I would be inclined to believe that prostitutes are only as-likely (and perhaps even less-likely) to have AIDS as compared to an equally promiscuous non-prostitute. Given the nature of their work, one would hope that they are at least informed of the precautions necessary to reduce* (*not prevent) disease transmission.  They might also be more likely to regularly schedule medical checkups for their reproductive health, since they are aware of the danger of their work.  The biggest problem with HIV transmission is the spread due to people who are unaware that they are carriers (thus they remain sexually active). Nimur 06:30, 19 February 2007 (UTC)
 * It appears that the statistics depend on the country (not surprisingly, there is a lot of variability in the reported results). In Africa, prostitutes have higher incidence rates because "Despite relatively good knowledge about AIDS and STDs, the reported preventive behaviour was poor.".  I have not been able to find relevant statistics for the US or UK. Nimur 06:35, 19 February 2007 (UTC)


 * Well, I hope you have no STD, since you're almost sounding like you'd be glad to have herpes or hepatitis. --Wirbelwind ヴィルヴェルヴィント (talk) 06:32, 19 February 2007 (UTC)


 * I hope you sought medical advice; like others have said, Wikipedia is not a doctor. The good news, however, is that the chances of catching AIDS from oral sex are pretty low, as our article explains.  While you're there, ask your doctor for some information on sexually transmitted diseases.   --Robert Merkel 06:38, 19 February 2007 (UTC)


 * A few things here:


 * The risk of getting HIV is not as high as you might think. If you are a man and received oral sex the chance is theoretically zero but some people have open cuts or something and it is a 5 in 100000 chance, which would be 0.0005%. You can roughly approximate the probability by multiplying the value of your location on the map by the value in the table.
 * HIV/AIDS is not the only disease. I'm not sure why people tend to think it is, is it because there are no visual cues and from media publicity?
 * Get a test, just because you're already so freaked out about it.
 * Learn about STDs while you're at the hospital. Information is power!
 * There you go, I haven't provided any advice but to see a doctor, and have only given objective information, and I hope this follows the new unofficial guidelines from medically-related questions. Good luck. [' Mαc Δαvιs '] X ( How's my driving? ) ❖ 07:38, 19 February 2007 (UTC)


 * Yes, there is a chance you haven't contracted it, but for the sake of your health it's best to have it checked. If you did get it, you'll be kicking yourself if you didn't visit the doctor. - 10:27, 19 February 2007 (UTC)

Be happy it isnt falling off (as a joke states here where we live) =) Maverick423 17:06, 19 February 2007 (UTC)


 * You say you are visiting London; are you a UK citizen? I only ask because I'm not sure quite how it works if you're not. Either way, you probably want to visit an NHS Walk-in Centre, or maybe a family planning clinic (?) , unless the helpline recommended a particular hospital? If they recommended some other sort of hospital, you should be able to navigate from the links I provided to find your nearest. Skittle 21:38, 19 February 2007 (UTC)

If you start post-exposure prophylaxis soon after an exposure, it will reduce the chance of getting the disease. --Spoon! 22:12, 19 February 2007 (UTC)

Minimalist Pancakes
So what are the ABSOLUTE BARE MINIMUM ingredients to make pancakes? Many recipes call for eggs, baking powder, blueberries, butter, etc.

Is it possible to make a simple pancake batter with nothing but flour and sugar and butter and milk? These guys say baking powder helps with the gluten. What else should I know? Nimur 05:18, 19 February 2007 (UTC)
 * Actually, they say without the baking powder they were "gluey". Baking powder doesn't affect the gluten (which is the elastic material in wheat flour), and in minimally-mixed pastries like pancakes, the gluten is hardly developed anyway (you don't want it to be, since it makes the final product tough and chewy).  The baking powder is there as a leaven, which means "thing that makes bubbles".  Bread-making usually uses yeast as the leaven, but very liquidy doughs (like pancake dough) need something faster-acting.  The alkali baking powder mixing with the dough's natural acidity releases carbon dioxide to provide the bubbles quickly.  Sometimes yeast is used in pancakes, but that's more for flavor than for leavening. --TotoBaggins 15:12, 19 February 2007 (UTC)


 * I successfully used only Flour, Sugar, Salt; Milk, Butter;  Cinnamon, and Blueberries.  This is only one data point, but I think it could be brought down from there.  (1 Cup flour, 3 TBSP sugar, 1 TBSP salt; 2 TBSP butter, 3/4 Cup Milk, if you're interested).  Nimur 06:19, 19 February 2007 (UTC)


 * You could, but usually the result wouldn't be called pancakes. If you email me on my userpage, I'd be happy to dig through my cookbooks for you. - Mgm|(talk) 10:24, 19 February 2007 (UTC)


 * You can make perfectly good pancakes with nothing but eggs, milk and flour, plus a little oil for frying, but you'll need something (sweet or savoury) to sprinkle or pour on the final product. Spiral Wave 13:32, 19 February 2007 (UTC)
 * Definitely - my standard pancake recipe is 1 egg, 1 cup of milk and 1 cup of self-raising flour - mix it all together then add a little more milk to thin it out a tad before pouring. You don't even need oil if you use a non-stick pan. What else would you call such things, Mgm, if not pancakes? Natgoo 18:22, 19 February 2007 (UTC)
 * Self-rising flour contains two ingredients, though - flour and baking powder. -- Charlene 16:05, 22 February 2007 (UTC)
 * With a few ingredients missing from that list you could make tortillas. They're flat and baked, but technically not pancakes. - Mgm|(talk) 08:34, 20 February 2007 (UTC)
 * Yep. Eggs, flour, milk. And, even while you're being minimalist, you could whisk it up tonight for tomorrow morning, or tomorrow morning for the evening, and leave it in a covered bowl in a fairly cool place. Something happens with the flour (probably involving gluten?) and the pancakes work better. Skittle 21:23, 19 February 2007 (UTC)


 * You might also want to subsitute seltzer (or maybe club soda) for the water in the mix. The carbon dioxide in the seltzer will act as a leavening agent, producing light and fluffy pancakes.


 * Atlant 18:28, 20 February 2007 (UTC)

You could just buy premade pancakes, which only have one ingredient-pancakes


 * Pancakes were originally a way to turn flour into food without perishables such as egg, milk, yeast (a perishable item before dry yeast was invented) and the like in the absence of an oven. Many old recipes call for nothing but flour, water, and baking powder. Using egg and milk make the pancakes tastier and more nutritious, but it's not an absolute necessity. -- Charlene 16:05, 22 February 2007 (UTC)

Dogs Tilting Their Heads
Why do dogs tilt their head when they percieve something as strange or confusing? PitchBlack 17:07, 19 February 2007 (UTC)
 * It might have something to do with that this is simply body language. You might as well ask why humans put on a puzzled face during the same circumstances. :) 81.93.102.185 17:40, 19 February 2007 (UTC)
 * They have such teeny little brains that they need to tilt their heads so that the bits of brain concentrate in one place. --jpgordon&#8711;&#8710;&#8711;&#8710; 17:54, 19 February 2007 (UTC)
 * This question came up before on the ref desk I think. Not sure when, but I recall someone suggesting it was to better locate the source of the unusually sound.  That seems plausible IMO. --Cody.Pope 18:02, 19 February 2007 (UTC)
 * Please don't post jokes as answers to reference desk inquiries. Some people may not realize you are joking. Thanks! Diletante 18:02, 20 February 2007 (UTC)
 * Some people do it too. I suspect (without evidence) that they are trying to get their ears into a more favorable position to catch the sounds they are trying to sort out. I suspect this because they move their ears around at the same time. I don't think it's just body language because they seem to do it even when they think nobody else is there...but who knows what goes on in those little furry brains? SteveBaker 18:03, 19 February 2007 (UTC)
 * Maybe for the same reason they sometimes cross their paws when lying down: their evolutionary strategy is to be unbelievably cute to humans. :) --TotoBaggins 18:57, 19 February 2007 (UTC)
 * Actually, that's not altogether a stupid answer - in an evolutionary sense, the genes that survive into the next generation are the ones that have the property of being the most pleasing to humans - so yeah - it's perfectly possible that the head-on-one-side thing is an evolutionary adaptation to their environment (ie to an environment where humans breed dogs). Certainly that is the case with floppy ears - which are entirely useless in any other survival situation. SteveBaker 03:21, 20 February 2007 (UTC)
 * Tilting the head would be something dogs evolved due to inadvertent pressures to be "cute", then. Floppy ears were deliberately selected for through centuries of dedicated breeding by humans - floppy ears have definite advantages for dogs tracking scents (they stir up the dirt, which can get more of the scent into the air). -- Charlene 16:10, 22 February 2007 (UTC)
 * Yeah, I would go for that along with providing for themselves a slight alteration in perspective. Sometimes when you call a dog that is interested in say a cat in a tree it will turn to let you know its coming  and  to see if you are really  calling them and if you really mean it. So it might really be part of doggy-to-human language and intelligence. 71.100.174.200 06:41, 20 February 2007 (UTC)

When Was The Last Planetary Alignment, & When Is The Next Planetary Alignment?
A response on my talk page would be greatly appreciated; thanks!100110100 19:47, 19 February 2007 (UTC)
 * Well I'm going to answer here anyway, planetary alignment is a bit of a misleading term. People consider 'alignment' to mean all in a straight line, but in astronomical terms, alignment can mean in the same region, or even just 'on the same side'. For example, there was a 'planetary alignment' in 1982 where all the planets were on the same side of the sun. Also, 'planetary alignment' can mean even just 3 planets are somewhat aligned, or just 2 planets and the sun. So planetary alignments of various significance are happening all the time, here is an article which treats the subject quite accurately. Vespine 21:53, 19 February 2007 (UTC)
 * When was the last perfect planetary alignment, & when is the next perfect planetary alignment? Thanks!100110100 22:13, 19 February 2007 (UTC)
 * If by perfect, you mean when all the planets were in the same line, then never. Since some orbits are tilted with respect to others it is not possible for them to really align.  As above, "alignment" is usually meant to indicate that several planets are in roughly the same part of the sky but it is not a very precise thing.  Dragons flight 22:18, 19 February 2007 (UTC)
 * How bout on the same plane.198.166.241.14 11:49, 20 February 2007 (UTC)
 * There are several types of alignment; as already said, they don't all have to be in a straight line. There was a grand cross sometime around the most recent turn of the century, for example. I think 5 or 6 planets were involved, and a straight line through planets on both sides of the Sun, so it was a fairly major astrological event, for those who are into that kind of thing. Spiral Wave 23:54, 19 February 2007 (UTC)
 * Just for completeness, planetary alignment says more or less the same thing as Vespine.--Shantavira 08:22, 20 February 2007 (UTC)

So what actually is the answer


 * The 'answer' depends on what specific question you're asking. As said, there is no such thing as a simple "alignment". It depends on what type of alignment you mean. If you mean "all the planets at exactly the same spot in the sky", as Dragons flight said, never. If you mean they're all in the same half, or quarter, or one-eighth, or one-sixteenth, other answers apply. -- Charlene 16:53, 22 February 2007 (UTC)

Venus flytrap redux
One of my co-workers has a venus flytrap on his desk. Ever so often, I'm devilishly tempted to stick my finger in it, just to tease it and see what happens. Just as a matter of interest, how hard are they capable of clamping down? --Kurt Shaped Box 23:00, 19 February 2007 (UTC)


 * Hard enough to take bothersome coworkers' fingers off. Why else would he keep such a thing around?  Seriously though, don't harass your workmate's plant. -- mattb


 * Please don't post jokes as answers to reference desk inquiries. Some people may not realize you are joking. Thanks! Diletante 17:59, 20 February 2007 (UTC)


 * You do understand that 1) most people do have a functioning sense of humor and 2) we're all volunteers here so there has to be some reward for everyone, questioner and answerer alike, right?


 * Atlant 18:39, 20 February 2007 (UTC)

very true a venus fly trap can only clamp shut about 8 times per leaf. each time it does it waste a massive amount of energy and fluids. the plant clamps shut cause it thinks there is food in the leaf however if there isnt food you just made the plant lose vital fluids and energy. doing this repeadtly will kill the plant as it is not getting any nutriunts back and is wasting alot of them. please do not tourture the poor little plants. i think your friend would be crossed if he ever found out that his little plant is being or is killed by you. Maverick423 14:23, 20 February 2007 (UTC)


 * Okay guys, I'm not going to mess with his plant - I swear. Just as a matter of interest then, how hard can they 'bite' down? --Kurt Shaped Box 17:45, 20 February 2007 (UTC)


 * Not at all hard, and it's fairly slow in action. Just trigger three little hairs...


 * Atlant 18:39, 20 February 2007 (UTC)


 * Yeah - it doesn't have to be fast or hard - just so long as the spines around the edges of the trap are interlocked, the insect is in a prison from which it can't escape. It doesn't die from being dramatically squashed - it basically dies from  starvation/dehydration much later on. SteveBaker 04:05, 21 February 2007 (UTC)


 * Thanks, guys. For some reason, I imagined a bear trap type situation (which is why I've never deliberately placed my finger inside one - I'm not *that* stupid). --Kurt Shaped Box 23:50, 21 February 2007 (UTC)

= February 20 =

venus flytrap reproduction
now i know u need a female and male reproductive orgin if i want to get some seeds but do i have to use up some of my money just to go buy another venus flytrap and thanks alot sumitt u'v helped alot uv probubly relized by now that im kind of desperet thx

01:13, 20 February 2007 (UTC)01:13, 20 February 2007 (UTC)


 * Venus fly traps are incredibly hard to grow from seed. They are pretty hard to keep alive anyway.  The biggest problem is that they need soil with relatively poor levels of key nutrients.  That's why they evolved the carniverous lifestyle - they need certain key nutrients that they aren't getting from the soil.   That also explains why they don't eat many bugs - in a well looked after condition with high nutrient levels in the soil - they just don't need to eat insects. SteveBaker 03:25, 20 February 2007 (UTC)


 * Why do you think you need to get a second one? Was this plant part of a science fair project or something?  Were you counting on being able to show it eating bugs?  Did my comment about damaging the trigger hairs make you afraid that your first plant is beyond saving?


 * If this is part of a science fair project or something, my advice to you is: change horses in mid-stream. This can feel like you're abandoning your goal, and it may make you feel like a quitter, but: this is exactly what happens in real Science all the time.  When an experiment isn't going the way they expected it to, successful scientists don't keep bashing their heads against the same brick wall.  They take a step back and ask, "Is there something else going on here?"  Sometimes, a failed experiment teaches us more than a successful one would have.


 * If, for example, your project was something along the lines of, "Why (or how) do Venus Flytraps eat flies?", you could stand this question completely on its head and appropriately ask, "Why does my Venus Flytrap not eat flies?" That's an interesting question, too, and you can find some good answers in the venus flytrap article, or right here in this thread.  Your flytrap may not have eaten anything, and that's too bad, but you're learning a lot anyway, and that's the important part. Good luck! —Steve Summit (talk) 03:43, 20 February 2007 (UTC)


 * Yes, indeed - there is a tendency to think that because you didn't get a spectacular result - or the result you expected - that you failed. But science isn't about that.  So long as you planned a valid experiment, carried it out correctly and recorded and interpreted the results - then the experiment is a success.  So - if your flytrap doesn't eat an insect - that's every bit as valid a scientific result.  In fact, the only really interesting scientific experiments are the ones that don't come out like you expect - because those are the ones that actually teach you something and start you off on a new line of research.  When Rutherford fired high speed particles at a thin sheet of gold foil - he was massively surprised to find that some of them bounced off - this was not at all what he expected - but it lead him to discover the atomic nucleus - which isn't bad for an experiment that didn't do what he hoped.  On the other hand, if you are a technologist and you need to produce a specific result in order to make something work - then you'll be pretty upset if you don't get the result you were hoping for...but that's the difference between doing science and making technology! SteveBaker 04:50, 20 February 2007 (UTC)

thx but no its not part of a science prject its just that i bought a venus fly trap but it wont eat or even close its trap for that mater. And i no that u need a female and male reproductive orgin but does the opposite sex orgain have to be from another plant or can it be from my original VFT. thx --Rsivad 01:25, 21 February 2007 (UTC)
 * It's just as well, really, since after they trap a fly or a bit of ground beef the trap turns black and falls off and in general detracts from the aesthetics of the plant. - Nunh-huh 01:48, 21 February 2007 (UTC)

Lorentz Force
I was trying to calculate the Lorentz force for a charge in a magnetic field of 0.9 tesla orthogonal to an electric field with 30 amperes of current. However, I keep coming up with very large forces. Should these numbers be this high? Around 10^16 newtons for the electric force alone. I'm trying to find what current I would need to push an electrically conducting fluid through a 1 cm diameter tube at a reasonable rate, maybe 10 cm/s. Does 30 amperes seem like overkill?


 * Without running any numbers, 0.9 tesla and 30 amperes are generally very large values. They seem reasonable for the scale of fluid pumping you seem to be after, but you're going to have some fun challenges building a system capable of generating and sustaining that much magnetic flux density and current. -- mattb


 * Yeah - 0.9 T is like the best neodymium magnet money can buy - or a really, really big iron magnet. A 1-T neodymium magnet can lift about 10 kg!  If you get your finger trapped between it and a chunk of iron, you are going to be in an awful lot of pain! SteveBaker 04:13, 20 February 2007 (UTC)

From Magnetic field

 * $$F = I B l \,$$

where
 * F = forces, measured in newtons
 * I = current in wire, measured in amperes
 * B = magnetic field, measured in teslas
 * l = length of wire, measured in metres (assume yours is 0.1 meters long)

so in your case you get
 * $$F = 30 * 0.9 * 0.1 = 2.7 Newtons \,$$

The longer the wire the more force you will achieve. So if your wire is 10 grams say, you will get an acceleration of 270 ms-2, and the wire will be flicked out of the field (I don't expect you can sustain your field over a very large volume!) GB 04:49, 20 February 2007 (UTC)


 * He was talking about fluid propultion (ala MHD) using Lorentz force. The equation for a wire segment is of limited utility here. -- mattb

The strongest electromagnets I know of are about 3 tesla, and are used for certain MRI and medical applications. I understand they can rip keys from you pockets through the fabric. --h2g2bob 13:49, 20 February 2007 (UTC)
 * I've seen 9 and 12 tesla magnets for MRI and similar scientific studies (I think something to do with high resolution mass spectrometry. But those were supercooled with liquid nitrogen (I don't know if they were electromagnetic or if they were just very powerful, but I do not believe they needed power to operate). Nimur 01:25, 21 February 2007 (UTC)

Dehydration reactions
Does adding sulfuric acid to sucrose to obtain charcoal count as a dehydration reaction? If so, since this is a pretty common demo, shouldn't it be in the article? --M1ss1ontom a rs2k4 (T 04:39, 20 February 2007 (UTC)


 * The Dehydration reaction is still a stub, so you cannot expect there to be too much detail, or many examples. The examples are all synthesis, turning sugar into charcoal is not a synthesis, but quite destructive.  The total reactions and atom rearrangements in this reation are quite complicated, even if the end result is simple carbon.  GB 04:55, 20 February 2007 (UTC)

It is a dehydration reaction and is counted as a synthesis of a particular form of carbon. There's no reason why a non discrete synthetic method shouldn't be added.87.102.36.28 14:49, 20 February 2007 (UTC)
 * I've addedd it therefor - feel free to add a link to a better demonstration/explanation if you have one.87.102.36.28 15:00, 20 February 2007 (UTC)

I have appended C6H12O6 + H2SO4 → Cgraphitic foam + 6 7 H2OGaseous + SO2

Beware that this reaction produces toxic sulfur dioxide and should only be performed in a fume-hood or well ventilated area.

I realize that this reaction is not balanced (it's been awhile for me, I'll try to work out the chemistry but if someone else gets to it first, please correct it). Nimur 01:37, 21 February 2007 (UTC)
 * I think I figured it out, but a chemist should check my work :) Nimur 01:39, 21 February 2007 (UTC)


 * Yikes, it seems I got the whole thing wrong. Apparently there is no SO2 produced at all.
 * I've done this experiment many times and I think possibly a small amout of SO2 is made - by some side reaction.83.100.252.90 13:40, 21 February 2007 (UTC)
 * I've re-edited it - the sulphuric acid water reaction was too specific to be used.83.100.252.90 13:46, 21 February 2007 (UTC)

Vitamin B
Why does vitamin B turn your urine yellow so quickly after taking a tablet of the vitamin? Why does it do this at all?

I'm not ill. I'm not seeking medical advice. I'm just seeking medical information. Dismas |(talk) 05:17, 20 February 2007 (UTC)
 * That's the color of the surplus vitamin B you're pissing away. When you excrete it, unchanged, through the kidneys, it colors your urine. - Nunh-huh 05:38, 20 February 2007 (UTC)


 * It works along the same scientific principles that cause a glass of water to turn red when you mix cherry koolaid into it... &mdash; BRIAN 0918 &bull; 2007-02-20 16:53Z
 * So how does the body know so readily that you don't need that Vit. B that you're pissing away? Dismas |(talk) 04:59, 21 February 2007 (UTC)
 * The body doesn't "know" anything! You absorbe the vitamins from your intestines into your blood. Your blood is filtered through your kidneys as fast as the heart can pump it there, and anything that isn't actively resorbed is pissed out. The B vitamins (other than B12) aren't stored anywhere or resorbed. Whatever isn't bound on the first pass through the body is lost. - Nunh-huh 07:02, 21 February 2007 (UTC)

Light Bulb
If a light Bulb produces heat, then if we were to enclose the entire light bulb in a high temp transperant vacuum chamber,would it not be more efficient as no heat leakage would arise towards the surroundig atmosphere??? —The preceding unsigned comment was added by 210.212.194.209 (talk) 05:38, 20 February 2007 (UTC).


 * By putting the bulb in a vacuum, I imagine all you'll be doing is causing the light bulb to heat up more than usual, since it can no longer lose (or is it loose? I never know...) the heat via convection. Basically, it doesn't matter what environment the light bulb is put in, it will always output a certain percentage of it's energy as light, and that percentage is dependent on what's inside the light bulb, and not what's outside. - Akamad 06:16, 20 February 2007 (UTC)


 * If the heat in the light bulb cannot escape into the surrounding environment then basically the amount of heat will increase over time. So eventually the light bulb will literally melt down. 211.28.127.77 07:03, 20 February 2007 (UTC)


 * The filament IS in (nearly) vacuum, and thus most heat that you feel (and the light that's coming out of it) is transferred as infrared light. There's no point in putting it in yet another vacuum. --antilivedT 07:14, 20 February 2007 (UTC)


 * Modern lightbulbs don't have a partial vacuum inside. That was the case back in the early days of domestic light bulbs - but modern bulbs are fulled with a fairly inert gas instead: Nitrogen, Argon, or Krypton.  But still - you can't alter the ratio of light in the optical part of the spectrum to that put off as infrared by enclosing the thing in anything - so you can't improve the efficiency that way.  What you'd probably do would be to dramatically increase the operating temperature - which would shorten the life of the bulb horribly. SteveBaker 08:00, 20 February 2007 (UTC)


 * The gas is at a very very low pressure, which still means it's in partial vacuum. Also, reflecting the infrared back in is already used per Lightbulb. --antilivedT 08:05, 20 February 2007 (UTC)


 * Most heat coming from a lightbulb is radiated as infared rather than transfered by convection. Much of the lightbulb's energy is lost as heat, and energy efficient lightbulbs are much cooler. See lightbulb for more details. --h2g2bob 13:43, 20 February 2007 (UTC)


 * I know that modern bulbs are not at atmospheric pressure with some inert gas inside, because they hiss when I carefully open the little glass tip inside the base, So what is the pressure and what are the gasses inside a modern bulb? In the 1870's/1880's the goal was to get the state of the art lowest possible pressure inside the bulb, and earlier attempts with inert gases failed miserably, with the filament burning out in 4 hours or less. Edison 17:15, 20 February 2007 (UTC)

The basic problem is that any practical material used as a filament has a certain melting point and it isn't very high, even for tungsten. The end result is that you end up with a black body radiator operating at a pretty low temperature and emitting most of its energy in the infrared portion of the spectrum rather than as visible light. No matter what you do, you're ultimately up against that problem of the melting filament. The best efforts to date have been with envelope coatings that selectively reflect the IR back into the lamp, allowing the filament to stay hot with less energy input (since less IR is leaving the system).

Atlant 18:47, 20 February 2007 (UTC)

Heat CAN transfer through a vacuum! This is called radiation. You are correct in assuming that convection would be eliminated, but that would not increase efficiency. Nimur 01:51, 21 February 2007 (UTC)

What's the name?
Where can I find the article fort those rotating lights one use to put on top of trucks and tractors to warn motorists with bad vision? Cops has them too, just they are blue. --Boongoman 08:02, 20 February 2007 (UTC)
 * light bar? --Spoon! 08:24, 20 February 2007 (UTC)
 * Tnx.. Was perfect. --Boongoman 08:34, 20 February 2007 (UTC)

Tsunami question
In the movie "Deep Impact" a megatsunami is caused by a comet fragment (picture of tsunami hitting New York: http://www.savelivesinmay.com/slimdocs/art-deep-impact-may-2006-En_files/image009.jpg or http://www.zdf.de/ZDFde/img/49/0,1886,2439985,00.jpg) and the wave gets as far inland as Ohio/Tennessee. According to the image from the movie, how high approximately is this tsunami, and could it theoretically really get so far inland? --AlexSuricata 11:01, 20 February 2007 (UTC)
 * I find that movies do not necessarily hold to anything scientific. I would assume that in the movie, an evil Harry Potter wizard made things worse... --Zeizmic 13:31, 20 February 2007 (UTC)

well if i remember correctly i recall hearing that any impact on earth with a reasonable size astroid like the one in deep impact will cause a wave of about 1000 feet high. gotta love discovery channel =) Maverick423 14:42, 20 February 2007 (UTC)


 * Well, the smaller chunk of comet (Biederman) is 1.5 miles (about 2400 m). According to this site, the amplitude the tsunami 1000 km from the impact point is $$h = 7.8 \times ((\frac{D}{406})^3 \times (\frac{V}{20})^2 \times (\frac{M}{3}))^{0.54}$$ where D is the diameter (metres), V is the velocity (km/s) and M is the density (g/cm3). Assuming the comet is pure ice, the density is near enough 1 and D is 2400. I don't remember them giving a velocity for the comet, but according to the article, the worst case scenario (this is a movie after all!) is 70 km/s. Plugging these numbers in gives an amplitude of 296 metres for a max tsunami height of 592 metres (height = 2 x amplitude). From what I remember, the water doesn't quite cover the World Trade Center, which would put the wave height at about 400 metres, so in face the wave should be even higher than in the film! Note however that the formula is meant for deep water: the land would probably cause a lot of friction and cause the wave to break. Laïka  17:46, 20 February 2007 (UTC)

Check out this site http://www.lpl.arizona.edu/impacteffects/ - you can enter the size, speed, etc of your comet or meteor - tell the program whether it's going to hit land or water - and what depth of water - and it tells you all about the dire consequences. It's a lot of fun to play with. SteveBaker 20:46, 20 February 2007 (UTC)

Thanks very much Steve & Laika! --AlexSuricata 15:14, 21 February 2007 (UTC)

LED torches and depth perception
I've noticed that when using an LED head torch (flashlight), my depth perception (particularly when looking at the ground) is noticeably less than when using an incandescent bulb light. Why is this? My best guess is that the blue-ish colour of the LEDs decreases my ability to pick out details and thus my eyes have more difficulty finding features to focus on. Does anybody know more? Maelin (Talk | Contribs) 12:40, 20 February 2007 (UTC)
 * The article Depth perception has some good explanations on this. --Zeizmic 13:33, 20 February 2007 (UTC)
 * It might be to do with the colour of the LEDs because we percieve different wavelengths of light at different focal lengths which might give us some really subtle depth cues. LEDs generally only produce light at a few specific wavelengths rather than all over the spectrum as an incandescant lamp does.   But that seems like a pretty hokey explanation to me - I don't buy it at all.  I strongly suspect it's because the light is mounted on your head.  Having the only source of light be very close to your eyes means that you can't see any shadows (they are all 'hidden' behind the object that's casting the shadow) and every object is lit from exactly square-on to your line of sight - which washes out the shading that you get when  you light something from off to the side.  Both of those things would certainly do bad things to your depth perception.  Try holding the same torch in your hand instead and see if things get better. SteveBaker 16:59, 20 February 2007 (UTC)

Accounting Policies & Procedures
Will anyone help me in getting a brief of the Accounting Policies & Procedures to be set before starting an accounting department in an organisation.

Just I need the minimum requirements in a para or 2, for a normal business unit.

Thanks


 * The United States Securities and Exchange Commission has dozens of tutorials. This question probably does not belong on the Science Desk, though. Your actions probably have legal implications in the United States .  Wikipedia cannot give legal advice.  Consider consulting a professional licensed attorney.  Nimur 02:12, 21 February 2007 (UTC)

Images of predicted sea level rise
hello,

Does any one know where i can find any, satellite images in particular, of what the world would look like with different amounts of sealevel rise, eg what land would look like with a rise of 10metres for example. (In particular the UK and Europe please).

thanks, --84.65.187.216 17:26, 20 February 2007 (UTC)


 * This may help . However, it is worth noting that satellite digital elevation maps generally have errors of +/- several meters, so the effects of small sea level rises should be taken as qualitative rather than highly precise.  More precise ground based measurements are available in some regions, but not globally.  Since sea level predictions for 2100 are less than 1m, it is basically impossible to generate reliable maps of what that will actually look like.  Dragons flight 18:12, 20 February 2007 (UTC)


 * NASA did a radar survey of about 80% of the earths surface (excluding the polar regions) from the shuttle several years ago. That data is vertically accurate to around 10cm and horizontally accurate to a few meters - and it's freely available to anyone who needs it.   But one of the things that makes this hard is that the weight of the oceans pushing down on the land causes it to squash a bit - as sea levels rise, the ground will be squashed - and that's really tough to predict. SteveBaker 20:38, 20 February 2007 (UTC)


 * Ummm, please provide a link. The ASTER 2006 DEMs, which are the most recent NASA product as far as I know, quote an accuracy of >= 7m .  I am fairly confident no one has 10cm elevation resolution from space.  Keep in mind that would be 1 part in 10,000,000 accuracy for a craft at a mid-level low earth orbit of 1000 km.  Dragons flight 21:12, 20 February 2007 (UTC)
 * The NASA web site is screwed up right now - it's timing out and taking HOURS to load a single page! When it gets back to normal, I'll try to dig out my source.  You may be right in what you said to me on my user talk page though - there is a big difference between 'absolute' and 'relative' precision.  I'm 100% certain they had 10cm relative precision - but I don't recall what the absolute number was.   I was using the data to generate 3D terrain visualisation - and for that, relative precision is what matters - but in answering this question, the absolute precision is all-important - so I may yet have to concede the debate to you on this one!  We'll see when NASA's site comes back up. SteveBaker 04:00, 21 February 2007 (UTC)

Tongue anatomy
What is the name of the part of the tounge that is the thin piece of flesh connecting the bottom centre of your tounge to the floor of your mouth? Zoobtoob 06:59, 20 February 2007 (UTC)
 * Look at Mouth (human), expecially the additional images. I think the section under the tongue is labeled with a name, there. --Mdwyer 18:23, 20 February 2007 (UTC)
 * And wouldn't you know it - it even has its own article! --NorwegianBluetalk 19:12, 20 February 2007 (UTC)

Chemoluminescence at home
I tried to read chemoluminescence article but I did not understand much. Could you tell me without complex science terms how I can make chemoluminescence at home and is there materials to make chemoluminescence in normal shops. Thanks! 193.65.112.51 19:12, 20 February 2007 (UTC)


 * You can buy those emergency lights at garages and in sports/camping stores. They are six inch long clear plastic tubes with a small glass tube inside that.  When you bend the tube, the glass breaks and the chemical inside the glass tube mixes with the chemical outside of it and the result is a fairly bright glow that lasts maybe 10 to 12 hours.   At the end of that time, you simply throw the whole thing into the trash.  No heat is produced.  The chemicals they use tend to be a mixture of hydrogen peroxide (which you could probably get a hold of) and some fairly esoteric chemicals (which you probably can't). SteveBaker 20:18, 20 February 2007 (UTC)

Loss of car's anti-lock braking system
Driving a Ford Mondeo yesterday, I realised that I could lock up the wheels when braking on the snowy road, even though it is equipped with anti-lock system (ABS). Also, the ABS light was on, as if something was malfunctioning. The anti-lock was absent for a whole trip but came back the next time I started the car. What can cause this? Was it something I did during the startup sequence (I'd like to be able to do it again)? It was freezing outside, but not extremely cold (between 0 degrees Celcius and -10 degrees Celcius). —Bromskloss 18:22, 20 February 2007 (UTC)

the break fluid is warmed by the engine so most likely this isnt the problem. perhaps a leak? but that would mean your breaks dont work period. ABS is something important. if you were to go out of control and your brakes lock you wont be able to stear your vehical. if the problem is corrected now i suggest you go and take it to a mechanic. also the ABS light tends to turn on whenever you put the emergancy lights on (since you wanted to recreate it) however it doesnt turn the ABS off. Maverick423 18:27, 20 February 2007 (UTC)
 * I don't think the Mondeo is an American model -- I'm using experience of American cars, here. They may be different wherever you are.  The ABS light will turn on when an error is detected in the ABS system.  Usually, the ABS system is disabled when the light is on. This will record an error code in the computer which can be recovered by a repair shop.  A self-test happens on every start of the car and throughout the drive.   In my truck, for instance, the light is off and the ABS works.  However, once I hit about 30MPH, a self-test happens that detects a fault.  The ABS light turns on, the system turns off, and it will stay disabled until the vehicle has been turned off for a day or more. --Mdwyer 18:37, 20 February 2007 (UTC)
 * ABS electronics generally work on the same principles regardless of country. A Hall Effect sensor on each wheel hub senses the rate of rotation, and when the computer senses that the wheel has locked up it lowers the braking pressure to allow it to grip.  If the computer thinks anything is amiss, such as a bad sensor (hall effect sensors are ideal for self-diagnosis) or bad solenoids, it will disable the system.  See a mechanic about diagnosis and repair.  --66.195.232.121 18:48, 20 February 2007 (UTC)
 * Lots of things can fail, but some common items are:


 * The four wheel speed sensors (mounted one at each wheel)
 * The main vehicle speed sensor (probably somewhere near the transmission/transaxle)
 * The hydraulic pump (if you have one)


 * And nowadays, in ESP-equipped vehicles, there are more sensors that tell the system about the current attitude of the car, steering inputs, accelerator position, etc.


 * With Bosch ABS, I know trouble codes are not locked up and you actually need to visit your dealer with the ABS light on or they can't use the computer to learn anything useful. This is a problem when the fault is intermittent.


 * Atlant 18:55, 20 February 2007 (UTC)

Thanks for your answers so far. I'd just like to point out that I know how the ABS system works and that a different braking technique is appropriate without it compared to with it. I want to recreate it simply because I want to try driving manouvers that aren't really possible with ABS turned on. Are there a startup sequence I can use for that? —Bromskloss 19:24, 20 February 2007 (UTC)


 * Some cars certainly do let you turn off the ABS. My MINI Cooper has a dashboard switch for turning off all of the traction control, ABS, electronic brake distribution, etc - so you can drive the car without electronic assistance.  When you next turn off the ignition, the ABS reverts to being 'ON' again the next time you start the engine.  On the other hand, my wife's Mazda Protege doesn't have such a switch.   If you can't find the instructions on how to do it from information in the owner's manual then you could try calling the nearest dealership - or perhaps look for an owner's club.  It's common to want to turn off the ABS and traction control for driving  on ice and for some motorsports - so there might be a way to do that. SteveBaker 20:10, 20 February 2007 (UTC)


 * If you want to disable it, I'll bet there's a fuse you can pull! Of course, you need to realise that driving without the ABS is more hazardous, blah, blah, blah... Like SteveBaker's MINI, my old Audi had a switch you could press; my new(er) Audi lets you turn off ESP but not the ABS (AFAIK). But remember that if you're trying to accomplish a bootleg turn, you can always use the hand brake/parking brake/emergency brake; it's not susceptible to the ABS system ;-).


 * Atlant 20:26, 20 February 2007 (UTC)

Where's the ICZN list of names?
I added Infobox Scientist to Frédéric Cuvier, and the author abbreviation used on many pages is "F. Cuvier". However, I couldn't confirm that anywhere; the ICZN site appears not to have any list of zoological author abbreviations the same way that there are reliable lists of botanists from IPNI? grendel|khan 19:36, 20 February 2007 (UTC)
 * It seems to be a paper book The Official Lists and Indexes of Names and Works in Zoology (published in 1987 in a single volume - ISBN 0-85301-004-8) gave details of all the names and works on which ICZN had ruled since it was set up until 1985; more than 9900 names were listed. Earlier editions go back to 1915. From .  Zoobank is an attempt to record all species names online, but you can't query by original author.

Faster than Light
hello,

If you had a rocket in space and you had say unlimited fuel, would there be any reason why you couldnt just keep accelerating up to the speed of light?

thx, --84.65.187.216 17:44, 20 February 2007 (UTC)


 * Sort of. At least, you could get close. Did you check the relativity article? Mdwyer 18:10, 20 February 2007 (UTC)


 * Basically, according to Einstein, as you speed up, your mass increases. As you approach the speed of light, your mass would tend to infinity. In order to move an object of infinite mass, you would need infinite energy, and there is not enough energy in the whole universe! Laïka  18:14, 20 February 2007 (UTC)


 * The closer you get to the speed of light, the more energy you need to get closer still. So you can (theoretically) get close to the speed of light - but you can't ever quite reach it no matter what you do.  Roughly, you could imagine that it takes 'X' amount of energy to get to 90% of the speed of light - then another X units of energy to get to 99% and another X units to get to 99.9%.  If you expended 10X units of energy, you might get to 99.99999999% of the speed of light - but you could never quite get past that last little bit no matter how much energy you have. SteveBaker 20:34, 20 February 2007 (UTC)


 * Well he does have unlimited fuel and thus he has infinite amount of energy and thus he CAN go at the speed of like. --antilivedT 04:09, 21 February 2007 (UTC)
 * Might take an infinite amount of time to get that fast. DMacks 04:14, 21 February 2007 (UTC)


 * It doesn't make sense to start with an argument like "infinite fuel". To start with, infinite fuel means you have infinite mass, which means you're not moving at all but that's really difficult to imagine because all movement is relative, so in what manner are you not moving? Never mind the fact that the entire galaxy would collapse instantly. OK so lets assume that you have infinite fuel but you're somehow weightless. Now you can travel at the speed of light no problem. Hell, you can get rid of most of the fuel. Why didn't you just try being weightless in the first place? 61.25.248.86 06:35, 21 February 2007 (UTC)


 * You might well be able to travel at the speed of light if you had unlimited fuel, but the fact we live in a real world where unlimited few is impossible kind of prevents that from ever happening, so the theory of special relativity still stands. - Mgm|(talk) 10:51, 21 February 2007 (UTC)
 * No, you really couldn't. Even the hypothetical case falls apart due to general relativity.  The best way we know how to travel at the speed of light is to consider a body with zero rest mass (for example, a photon). -- mattb
 * Oh, and we forgot about having to overcome collisions with misc cosmic particles, solar wind, radiation pressure, and gravity, so it would take more energy than just "accelerate to c". Oops. On the other hand, would be cool to reach c in the (relative) vacuum of space then smash into the atmosphere of some planet and get to experience the brilliant Cerenkov radiation of oneself slowing down. Um, for the instant before you burn up as a plasma. DMacks 11:35, 21 February 2007 (UTC)
 * The good news is that in order to hold infinite fuel, your spaceship must be infinitely large, and therefore some part of it has already reached your destination. :) --TotoBaggins 17:17, 21 February 2007 (UTC)
 * Well, in fact, your destination is already sitting there somewhere inside your gas tank! If you have infinite fuel but finite size, your spaceship is going to undergo sudden and spectactular gravitational collapse - so instead of that shiney red spaceship. you'll have a small, smoking black hole sitting out in the parking lot.  But - even with infinite fuel - you still need an infinite amount of time (presuming you have finite sized rocket engines. SteveBaker 20:08, 21 February 2007 (UTC)
 * This is approaching infinite silliness. Clarityfiend 22:20, 21 February 2007 (UTC)

End of humanity, as we know it
Hey guys, just some morbid curiosity here, If a nuclear war were to occur, what are the chances of the human race carrying on? I understand that any survivors (if there were any) would have a totally different lifestyle, but could anyone actually carry the species on, or would the number of survivors be so few that we would be functionally extinct? If nuclear war were to occur, what would survivors eat and drink? Important officials (eg. the president of the USA) may be safe in their bunkers, but how long would they have to remain down there? If longer than a few human generations, how many would have to enter the bunker to make a viable 're-population program' to repopulate the earth without inbreeding. In other words what number of a species do you need to make a gene pool large enough? Thanks, in advance, for any replies,

Dave 88.111.82.185 17:56, 20 February 2007 (UTC)

Discovery channel once stated that it would take 214 people in a space capsule to reproducefor a 120 year journy in space without inbreeding. in this case to repopulate the world we would need well over 2000 or more. the human race is very much like a parisite that you cant get rid of easy. if we survive a nuclear winter then the race should go on. as far as food or water is concerened boiling water purifys it. fire can be made from rubbing sticks (or matches) and some rocks. insects are likly to survive the winter (especally cockaroches) which are edible. we will have shelter from homes that survive the blast. some power plants might survive as well. really when you look at it it doesnt signify the end of the world just a new begining. the only thing you should worry about is surviving the inital blast. after that your insticts will take effect and darwins law will start to take over Maverick423 18:10, 20 February 2007 (UTC)
 * Check out the generation ship article. --Cody.Pope 18:12, 20 February 2007 (UTC)


 * Thanks guys, this is pretty interesting stuff. I remember hearing about cockroaches being particularly likely to survive, but do you think they could really be used as a source of nutrition? I do not know how quickly they reproduce to be able to contain enough 'meat' to sustain a balanced diet. The generation ship is also a great idea/point, one that i had not thought of, for surviving after nuclear war, it could potentially be put in orbit instead of using bunkers to house people, for a few generations, very clever. Again thank you, i must also comment on how amazed i am at the quick response, this is the first time i have used wiki reference desk, it has really impressed me, i will be sure to use it in future for any points i wish to discuss or need information on, its good to have a community of like minded people who are willing to help :D thanks
 * (oh any further points which people have, are still appreciated, go ahead post them, they may lead to further trains of thought for me)


 * Dave 88.111.82.185 18:55, 20 February 2007 (UTC)

not a problem acctually cockaroches reproduce quite rapidly. it is said for every roch you see running around your house there are 1000 hidden withen the walls (saw this on National Geo's nightmare creatures) Rats are also a good example as per the roches 1 rat = 12 withen the walls. food sources will be qite numorus everywhere we just have to know where to look. Maverick423 19:10, 20 February 2007 (UTC)


 * The reason that small, short-lived creatures are particularly suited to survival is that they are pretty much unaffected by moderate levels of radiation. If you expose a human to moderate amounts of radiation, then 5, 10 years later, they develop some kind of nasty cancer and die.  That's pretty serious because we don't reach breeding age until mid-teens.  If the same thing happens to a cockroach, it's irrelevent that it's going to develop a cancer 5 years later if it's going to be dead of old age by then anyway.  Warm-blooded creatures are also a problem because we can't do without food for very long.  A crocodile can live for six months to a year without eating by lowering it's metabolic rate and simply lying there until food comes along.  Warm blooded creatures like us need food pretty much every day in order to run our 'always-on' metabolism.   So we're pretty terrible at surviving hardships biologically.   However, we're also smart and very adaptable - it seems really unlikely that we'd go totally extinct no matter what. SteveBaker 20:27, 20 February 2007 (UTC)


 * The BBC film documentary Threads tries to paint a realistic picture of what might happen and I recommend it. Better to make sure that it doesn't. --Seans Potato Business 23:57, 20 February 2007 (UTC)


 * I'm still of the opinion that our planet already survived nuclear holocaust. It was pretty intense and a lot of people died tragically, but it's hardly the global apocalypse that science fiction alarmists would have us believe. Nimur 02:17, 21 February 2007 (UTC)
 * There is a very good reason for that. That was just two bombs - one of a mere 13 kilotons and the other of just 21 kilotons.  Read about the Bombing of Dresden in World War II - about 10,000 tons (ie 10 kilotons) of conventional high explosives and incendiaries were dropped on Dresden - so whilst it took longer to deliver them - the results were pretty comparable to Hiroshima.  But both of those explosions in Japan were tiny by 'cold war' standards.  Both US and Russian arsenals contain 50 megaton weapons - 2,500 times more powerful than the Nagazaki bomb, 3,200 times as powerful as the Hiroshima bomb!  The effects of letting off dozens or perhaps even hundreds of those would make the horrific annihilation of those two cities look like a minor skirmish.  There was no nuclear winter following the two bombs that were dropped on Japan - no long lasting radioactive fallout drifting halfway around the world.  Yeah it was bad - but that's just NOTHING compared to what we're talking about here.  SteveBaker 03:54, 21 February 2007 (UTC)


 * I'm merely saying, we have exactly two data points in the entirety of human history by which we can gauge nuclear war. A lot of fiction has been written about a global nuclear missile strike with hundreds or thousands of weapons obliterating our entire planet. Yet, in the context of real history, the actual use of nuclear weapons seems to be only as a last-resort measure in the closing stage of a very long, very large conventional war.  In light of numerous wars fought since the development of nuclear weapons, a valid conclusion is that none have been severe enough to warrant ANY nuclear strikes, let alone "hundreds" of ICBMs.  Though many people tout mutually assured destruction as a realistic policy, it does not seem necessary, realistic, practical, or in tune with what actually has played out throughout more than 50 years of available nuclear weaponry.  Once again, we have very few data points on which to gauge nuclear war.  Yet, the "sparse" use of nuclear weapons in Japan as a final solution to a long and bloody war seems more plausible than an unrelenting global missile strike. Nimur 05:20, 21 February 2007 (UTC)
 * Another way of looking at that "sparsity" is that the US used every last nuclear weapon it had available. --TotoBaggins 17:22, 21 February 2007 (UTC)
 * Exactly. The usual assumption for a full scale nuclear exchange between super-powers is that around 3,000 Megatons would be unleashed within a few hours.  Compared to 34 kiliotons...well, there simply is no comparison.  Now - you might well argue that now that the "cold war" is essentially over, we don't have to be too concerned about this happening - but that's a different argument.  These days, we should be more concerned about India and Pakistan lobbing a few 10 kiloton weapons around - or North Korea "losing it" and dumping a couple of their 1 kiloton devices onto Japan - or maybe Iran dumping one of similar size onto Israel.  It's hard for any of those to escalate into the hundreds of megatons disasters we contemplated during the cold war - and the consequences of such events probably would be pretty similar to Hiroshima and Nagasaki - with little of consequence happening to the rest of the world as a direct consequence.   Of course many of these new nuclear powers only have a tiny handful of these low-yeild weapons.  They know that if they use them - the can't easily replace them - and the retaliation of the rest of the world would be unacceptable to them...so maybe this is still a stand-off. SteveBaker 20:00, 21 February 2007 (UTC)


 * You sure it was the Discovery Channel? I could have sworn I saw the 214 people in space capsules in a Naked Science episode on National Geographic. --Wirbelwind ヴィルヴェルヴィント (talk) 03:21, 21 February 2007 (UTC)

I guess, just like all war, it would depend on the severity. --Tbeatty 04:51, 21 February 2007 (UTC)


 * Bon soir to all, i read the article on mutually assured destruction, again some very interesting points made in the article, made me think somewhat about the futility of it all, but now we are getting into the ethics and philosophy not science. Is there any articles or links people have on advice for people (normal citizens) in the event of nuclear war, not that i expect one anytime soon, but it would be interesting to see what combats radiation in the home, thanks to all.--Dave 88.111.82.185 19:33, 21 February 2007 (UTC)


 * A few notes. Threads was produced in 1984 at the height of the "second" Cold War. As this graph shows, that was one of the peak times of total stockpile highs (60,000 warheads, primarily between the US and USSR). Current global stockpiles are considerably less, and the total megatonnage has dropped quite a bit (though I don't have that figure at hand); now it is more around 26,000, or a reduction by 60% or so. That being said, if we were to assume an all out exchange between the US and Russia, the results would be quite horrible still, even if they only targeted military installations. Would it cause extinction? Not immediately. It could potentially disrupt resource networks and even things like the climate and lead to quite a long period of very, very unpleasant times — even without contemplating the political and economic effects in any detail — but I don't think it would likely lead to extinction, per se, at least not immediately. --24.147.86.187 05:01, 22 February 2007 (UTC)

Magnetic Field Density
I can't seem to figure this out from the the magnetic field article, how can I calculate the magnetic field density purely by calculations? I only know the pull force on a steel alloy, 74.2 lbs, and the distance between magnets, about 1/2 a cm.


 * I don't think that would be particularly easy to calculate. You'd need the alloy's permeability and the magnet's field strength, and even then I think you'd only be able to work out a rough estimate. -- mattb


 * I went through four years of university physics and I never learned the answer to that exact question. It had plagued me since early in grade school.  They have such a nice law for electrostatics, but there's no easy one for magnets!  Magnetic fields are much less ideal, in general; they curve in weird ways, they interact with their source; time-varying properties are probably larger than the static effects... field lines don't even terminate on the magnet!  Your best bet is to use an engineering approximation and perhaps make a table of the force, distance, and any other control variables you find useful. Nimur 02:24, 21 February 2007 (UTC)

Look at magnet. It has the force equation.


 * $$F={{\mu q_{m1} q_{m2}}\over{4\pi r^2}}$$

where
 * F is force (SI unit: newton)
 * qm1 and qm2 are the pole strengths (SI unit: ampere-meter)
 * &mu; is the permeability of the intervening medium (SI unit: tesla meter per ampere or henry per meter)
 * r is the separation (SI unit: meter).

I think in your case, qm1 and qm2 reduce to q2 and a single unknown. --Tbeatty 04:29, 21 February 2007 (UTC) --Tbeatty 04:29, 21 February 2007 (UTC)


 * I must respectfully disagree with this equation. This is a common "analogy to Coulomb's law" form, but it is not a real physical equation (nor is it particularly accurate).  Most importantly, there is no way to measure the qm in either a practical or theoretical way. Nimur 04:01, 22 February 2007 (UTC)