Wikipedia:Reference desk/Archives/Science/2008 January 14

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< January 13 << Dec | January | Feb >> January 15 >
Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.


January 14[edit]

Why does food taste delicious?[edit]

If a kind of pizza evolved that was really bad-tasting, nobody would eat it, so it would eventually dominate all kinds of pizza cause those kinds would run out, you know? So why doesn't that happen in nature? Everything tastes so delicous! It's just begging to be eaten by predators! Like lettuce.. it's buttery and sweet and goes great with a strong vinaigrette. Why doesn't it get edged out by a spiny lettuce that gives you indigestion? --f f r o t h 00:06, 14 January 2008 (UTC)

Many yummy foods actually exist to be eaten. More specifically, they contain seeds that are sufficiently robust to survive attempts at being eaten, either because they are too hard to consume (think peach pits) or because they don't mind passing through the digestive tract of their naturally occuring consumers (think watermelon seeds). The act of being eaten (or trying to eat) helps the plant by moving the seeds farther from the parent. Such dispersal can increase the odds that some of the seeds will eventually find furtile ground. If you just dump your seeds year after year on the same spot, that will generally do little to advance the species.
That said, other plants, including lettuce, do not have seeds in their yummy parts. I don't know what advantage (if any) lettuce gains by being yummy. I will however note that iceberg lettuce and some other varieties were actually bred by man from ancestors that were comparatively bitter. Dragons flight (talk) 00:28, 14 January 2008 (UTC)
Whatever function iceberg lettuce may have, it's certainly not to taste good. Someone once opined that there's nothing wrong with the stuff; it had just been misidentified: It's not a food, but rather a building material. Something along the lines of fiberglass insulation.
I'll take a pure arugula salad--without even any oil, if ncessary--over iceberg any day of the week. --Trovatore (talk) 05:34, 14 January 2008 (UTC)
Vegetables store energy and nutrients for the plant. Like plants, animals require energy and nutrients, so out bodies have evolved to appreciate their taste. Nevertheless, plants do make efforts to make their nutrient stores unattractive, making tannins and alkaloids, spines and thorns to discourage animals from eating them. The reason so many of the plants we eat today appear, on the face of it, to be so evolutionarily disadvantaged is because they are. We made then nice and tasty by selective breeding, breeding out the bitter chemicals, the spines and the selecting for the juicy flesh. Wild vegetables are very different from the cultivars we eat today. Rockpocket 00:49, 14 January 2008 (UTC)

moreover, if a kind of pizza was bad tasting, it would remain on the shelf till midnight, yes. But would Dominoes make the same pizza again the next day? Kushalt 01:04, 14 January 2008 (UTC)

Yes of course. Dominoes make bad pizza every day. And hundreds of times a day. All their pizza is terrible, at least in Australia. Rfwoolf (talk) 05:26, 14 January 2008 (UTC)
It doesn't surprise me that dominoes make bad pizza. But who would think to make pizza out of dominoes in the first place? --Trovatore (talk) 02:48, 17 January 2008 (UTC)

I think that you'll find that most of the deliciousness is the product of thousands of years of artificial selection. Wild variants of most of the things in your salad would not be nearly as yummy. This is why animals are so interested in getting into your garden. There isn't anything nearly that yummy on their side of the fence. APL (talk) 01:07, 14 January 2008 (UTC)

Unfortunately, taste is not the only selective factor in the history of cultivation. Other aspects, such as yield, climate and disease resistance, or preservability got factored in as well. In my opinion, wild strawberries taste so much better than those big watery blobs sold at grocers. The same goes for other berries, not to mention the variety and tastes of wild-growing mushrooms compared to shiitake and champignons. </rant> ---Sluzzelin talk 02:15, 14 January 2008 (UTC)
There are also many examples of symbiosis between the vegetable and animal kingdoms. For instance, consider navel oranges and clementines. These plants have, most paradoxically, disevolved their own ability to independently reproduce. Yet this peculiar adaptation ends up conferring such an advantage in tastiness that certain animals are willing to artificially reproduce the plants for them, in order to enjoy fruit without seeds. Paradoxically, the seedless varieties end up reproducing more profligately than their seedful brethren, and are thus selected for (at least in the niche consisting of tended orchards). —Steve Summit (talk) 02:12, 14 January 2008 (UTC)

The reason those plants dont get edged out is that the gardeners pull out the horrible tasting stuff, like dandelions, summer grass, couch, wire weed, spurge etc that for example shows up in my vege plot. I leave the tomato and lettuce plants. But rabbits come and eat the lettuce! Graeme Bartlett (talk) 06:25, 14 January 2008 (UTC)

Dandelion greens aren't horrible tasting!--The Fat Man Who Never Came Back (talk) 06:32, 14 January 2008 (UTC)
Another way of looking at it is that all the animal species who didn't find at least something tasty to eat have all gone extinct from hunger. --Sean 14:03, 14 January 2008 (UTC)
See how well being delicious has helped lettuce! It’s grown on six continents and is in no danger of dying out. Compare this to all the awful tasting wildflowers that are at the brink of extinction. Same thing with dogs; they’re cute and cuddly so they live everywhere with our help. The gray wolf isn’t quite so lucky. --S.dedalus (talk) 02:21, 15 January 2008 (UTC)
Seems to me this assumes facts not in evidence. Who exactly thinks lettuce is delicious? I mean, romaine and radicchio are OK, I guess, but iceberg is appallingly horrible, and none of them are as good as spinach or arugula or "field greens" in general. --Trovatore (talk) 01:50, 17 January 2008 (UTC)
Iceberg may not be tasty, but it doesn't taste of much. It provides a structural matrix to many salads that tastier lettuce just can't support. Combined with not tasting of much, I find this makes it a perfect choice in certain salads, spacing the tastier ingredients and ensuring even coating with the dressing. Skittle (talk) 17:28, 17 January 2008 (UTC)
Well, de gustibus, dude. To me crunchy, wet, and tasteless equals gross. The thing that's not a matter of taste is that iceberg has essentially zero nutritional value -- at best it takes up room in your stomach, which possibly could keep you from eating worse things, but given that most people slather it with some disgusting sauce, even that's a dubious proposition.
As for me, give me a salad of bitter greens with just a little olive oil, salt, and lime, and possibly some red bell pepper, tomato, and/or very ripe avocado, and I'm good. If I'm feeling extravagant I might throw in some feta or kalamata olives. --Trovatore (talk) 18:31, 17 January 2008 (UTC)

What will happen if...[edit]

What will happen if you add a fluid to magma?98.224.10.129 (talk) 01:07, 14 January 2008 (UTC)Brain

What sort of fluid are you thinking of?--TreeSmiler (talk) 01:11, 14 January 2008 (UTC)
The natural fluids in magma, are the magma itself, water, Hydrogen chloride or carbon dioxide and maybe sulfur dioxide. Under pressure, these gasses can become liquids and dissolve in the molten rock. However if a volcano errupts under water, you get pillow lava as themolten rock is instantly frozen. without pressure the liquids will be vapourized. Some other kinds of liquid like petroleum will not be miscible in magma, and will decompose to simpler hydrocarbon gasses and carbon. Graeme Bartlett (talk) 05:59, 14 January 2008 (UTC)

Odd question[edit]

One day in my science class, being the smartass that i am i asked my teacher what would happen if hypotheticly you could swallow lava without dieing. well she basicly just ignored me and went on teaching which led me to wonder what would happen to it. Would it harden or would you eventually piss lava out? Also if it would harden could u survive by like having surgry to have your stomach competly cut open? BonesBrigade 02:26, 14 January 2008 (UTC)

Well, do realize that it's a question so absurdly hypothetical that it's nearly impossible to answer with anything remotely approaching "correctness". Obviously, in the real world, if you tried to drink hot lava, you'd burn your mouth and probably your whole head off before a drop of the stuff ever reached your stomach. We have to suspend so much disbelief (or, rather, ignore so many laws of nature) in imagining that you could drink it like any old thick, hot liquid that in that altered reality, there's no telling what would happen next.
My best answer is that you'd end up with a big chunk of solidified rock in your stomach which you could neither digest nor pass, and which would therefore lead to rather severe gastric distress. Or maybe, if you happened to have a relatively full stomach already, when the hot lava hit the rest of the food and liquid in your stomach, it would sputter and solidify in lots of separate little fragments, which you could try to pass (but which would probably only end up causing different kinds of gastric distress further down). —Steve Summit (talk) 02:39, 14 January 2008 (UTC)
(after edit conflict and lava break) Interestingly, your question isn't that odd. See "Would it be physically possible to drink lava?" Your caveat "without dying" makes the question very difficult to imagine. Lava "is a liquid at temperatures from 700 °C to 1,200 °C (1,300 °F to 2,200 °F)". Maybe the question needs to be rephrased for a non-toxic substance with a melting point somewhere between body temperature and very hot coffee. Of the elements, rubidium, white phosphorus, and potassium fit the temperature frame, which leaves us with their toxicity. ---Sluzzelin talk 02:44, 14 January 2008 (UTC)
Those three would mainly leave you with the fact that they would explode if you tried to eat them. Someguy1221 (talk) 02:55, 14 January 2008 (UTC)
Other metals I can think of would be cesium (which would also explode) or gallium. I'm not sure what would happen if you drank gallium. Someguy1221 (talk) 03:01, 14 January 2008 (UTC)
I imagine you could probably swallow very small amounts of lava and survive. I say this because my grandfather was a welder during WWII and once when welding in a small enclosed space inside the hull of a ship, managed to get a pea-sized globule of molten metal catapult into the back of his mouth. Before he could react it slipped down his throat, still as a liquid. He told me he has burns to his throat and a bit of moderate stomach pain for a day or so, but apart from that was fine. He passed the metal - now solid - a few days later. Rockpocket 02:49, 14 January 2008 (UTC)
I'm a bit skeptical of your grandpa's story, specifically the part about it being "still liquid" when he swallowed it. I suspect it cooled enough to solidify during it's flight through the air, but was still hot enough to burn him. After all, how would he know it was liquid when he swallowed it ? The ability to detect the difference between a solid and a liquid would certainly be lost due to the high temperature of the object. StuRat (talk) 13:34, 14 January 2008 (UTC)
I expect he couldn't know for sure it was still liquid when swallowed, however he had been scarred with enough globules of liquid metal that had hit his skin (to which I can testify, even 50 years later, those scars remained) to be familiar with what the state of those globules are. It seems fair to assume that if they hit your skin still liquid, then they would probably hit your throat still liquid. Rockpocket 18:01, 14 January 2008 (UTC)
....AWESOME!!! BonesBrigade 02:58, 14 January 2008 (UTC)
A Google search brought up the statement that crematoriums use temperatures of about 1500 degrees Fahrenheit for several hours. There was also a mention of the fact that soft tissue burns at a much lower temperature than bone though. My guess would be that lave would not instantly sear through your cheeks or whatever. Your muscles would probably be instantly disabled though making swallowing difficult (assuming we’re not talking about the apparently very small sample of molten material in Rockpockets example). Wow, this topic’s very macabre. --S.dedalus (talk) 05:05, 14 January 2008 (UTC)
You'd probably be spending a lot of time in the lavatory. --Sean 14:09, 14 January 2008 (UTC)
You'd be shitting bricks passing rocks for a week ! Astronaut (talk) 03:14, 15 January 2008 (UTC)

Name of medical condition ?[edit]

I seem to recall that consuming too much of some mineral causes nodules to form under the skin containing that mineral. However, I forget the mineral and the name of the condition. Does this sound familiar to anyone ? --StuRat (talk) 03:53, 14 January 2008 (UTC)

Agyria is caused by silver deposits under the skin. Gout also sometimes progresses such that tophi grow under the skin. --Mdwyer (talk) 20:17, 14 January 2008 (UTC)

A delicious 9V battery[edit]

OK so a 9 volt battery will shock you if you put its terminals on your tongue. So what would happen if you swallowed it whole? Assuming it fell into a position where both terminals were touching your stomach lining, would you feel the shock? Would it damage your tissues? Would the shock last until evacuation? HYENASTE 04:03, 14 January 2008 (UTC)

Amazingly, this seems to be a popular pastime there are many google links. This is just one [1]--TreeSmiler (talk) 04:13, 14 January 2008 (UTC)
A standard 9V battery is a cardboard case with six tiny 1.5V batteries inside of it. Those have a very thin casing that is easily crushed between your fingers. So, the battery will not stand up to stomach acid for very long. I did an experiment with putting one in a glass of water. The battery turned to mush rather quickly. I strongly suggest you try it in a glass of water instead of swallowing it. It is simply stupid to risk your life so you can say you swallowed a battery. -- kainaw 04:40, 14 January 2008 (UTC)
Cardboard? I have here a 9V battery. Just as with any other 9V battery I remember handling, the casing feels like metal. If I look at how it's crimped, it looks like metal. And if I scrape off a bit of the paint then my ohmmeter shows that it conducts electricity. So I don't think it's cardboard! The two ends of the battery do seem to be cardboard, though. --Anon, 07:03 UTC, January 14, 2008.
I'm in England. I've looked at three makes of 9v battery, all are certainly metal-cased but the two end pieces seem to be plastic. I doubt they would be cardboard. So not very digestible!! - Adrian Pingstone (talk) 08:35, 14 January 2008 (UTC)
This confusion arises because there are two styles of 9V batteries. The modern style is, indeed, 6 cylindrical alkaline cells (smaller than an AAA cell) wired in series and enclosed in an outer steel container. But an older style of 9V battery was made from six flat, rectangular carbon-zinc cells stacked up to form the series circuit. These older batteries of cells were then coated with wax and wrapped in paper or cardboard.
Atlant (talk) 19:02, 14 January 2008 (UTC)
That makes perfect sense. When I did my "experiment", I was in the Marines. Everything we received was old junk given away from some other military branch. For example, my M16 had a stamp inside the grip marking it as a reject from the Air Force. So, it is no doubt that we had old batteries - or even new ones that were so cheap that they used cardboard instead of plastic. -- kainaw 20:22, 14 January 2008 (UTC)
Don't get carried away playing with the battery—see Steve Baker's link to the Darwin Awards. -- Coneslayer (talk) 13:45, 14 January 2008 (UTC)
See also pica. --Milkbreath (talk) 18:57, 14 January 2008 (UTC)
Atlant: even modern Zn-C 9V batteries are made of rectangular cells, at least in the UK, except that the wrapper is now metal and not cardboard. (Example here) --Heron (talk) 19:27, 14 January 2008 (UTC)
What an excellent example of detailed forensic? work by J. Broncks. Now I dont have to do the same!--TreeSmiler (talk) 19:43, 14 January 2008 (UTC)

Body Language[edit]

Dear Sir/Ma'am,

Do you know of someone who can clean up the page on body language. I asked one of the moderators of the category but they sent me here. —Preceding unsigned comment added by Dez82 (talkcontribs) 08:26, 14 January 2008 (UTC)

If you haven't already, you could also try the Humanities desk here [2] since this may be a Behavioural science and/or psychology related article. Julia Rossi (talk) 09:22, 14 January 2008 (UTC)

water and fire[edit]

OK. possibly a daft question, or more likely one that's asked on a very regular basis. If hydrogen is flamable, and oxygen is fuel to fires, why is water not flamable? How can it be one of the best things for putting out a fire? Also, why is it wet (liquid) when its components are gasses?

thanks 83.104.131.135 (talk) 10:46, 14 January 2008 (UTC)

When you add hydrogen gass and oxygen gass together and add just a little bit of heat you get a big woosh (or a plop depending on who you ask). A lot of energy is released in this reaction. The reason for this huge amount of energy is that water(H2O) is a very stable state for hydrogen and oxygen to be in. Thus water doesn't really feel like reacting with anything else anymore.

Another way of looking at it is that burning is a form of oxydation. But the hydrogen in water has allready been oxydized (by oxygen) thus it won't react any further.

Why is water a liquid and not a gass? well the answer lies in hydrogen bonding. If there was no hydrogen bonding water would be a gass.PvT (talk) 11:20, 14 January 2008 (UTC)

To clarify, hydrogen and oxygen tend to attract each other (see hydrogen bonding). This means that the water molecules will try to stick together as the hydrogen bonds pull them together - this stops the molecules from flying around freely (as happens in a gas). Laïka 12:46, 14 January 2008 (UTC)


thanks everyone for the answers so far. Laika - your explanation of the water/gas thing was very clear - thanks. As to the others, if you're saying that when the oxygen and hydrogen combine, the hydrogen burns. Once this is 'spent' then what's left is water which won't burn because they hydrogen has run out of energy. Does this mean then that (outside of a labortatory perhaps) no new water is created? (in terms of rain/seas whatever) Because there's a distinct lack of explosions when it rains (which, thinking about it, might be fun!) cheers! 83.104.131.135 (talk) 13:05, 14 January 2008 (UTC)

Some water may be created during events like lightning strikes high in the atmosphere where there may be some free hydrogen. Very little water is created per year, but it can add up over billions of years to quite a bit. One theory is that most of the water came from early in the solar system's history, either created on Earth during that violent period or created on meteorites and comets as ice, with these objects later hitting Earth and delivering the water that way.
Also, the use of water to fight fires is because it uses up a lot of heat energy to boil water, thus hopefully cooling the fire down below combustion temperature and putting out the fire. StuRat (talk) 13:26, 14 January 2008 (UTC)
It's not quite true that no new water is being produced - every day, your body makes about 0.4 litres (just under a pint) of water out of fats, sugars and proteins. It's not much on a global scale, but it's enough for many animals (such as many arthropods and desert animals) to survive on - see Fluid balance. Likewise, burning chemicals such as petrol or sugar releases a bit of water as the hydrogen in the fuel reacts with oxygen from the air. This happens because although the hydrogen loses some of its potential energy when it reacts to form the fuel, it still has more energy than it would if it became water. Laïka 16:12, 14 January 2008 (UTC)

Traditional Japanese sitting arrangement[edit]

Before martial arts lessons, and while eating in some Japanese and possibly other Asian arrangements, people kneel with one foot slightly overlapping the other. Is this actually sensible or liable to cut off circulation? I also tend to get a cramp in my foot if my toes are bent towards the sole (downwards with respect to the foot as opposed to upwards). If I've oversimplified the posture somewhat, someone more worldly might set the record straight shortly. ----Seans Potato Business 12:41, 14 January 2008 (UTC)

The position is known as seiza. Our article states that among those with little experience of seiza, "maintaining it for more than a minute or two tends to lead to loss of circulation, with the accompanying 'pins and needles' feeling, followed by painful burning sensations, and then eventually complete numbness in the legs. However, the physical discomfort lessens with experience as the circulation of the blood improves". Much like any other unusual posture, repeated practise improves flexibility and circulation. Special cushions are also available which support the legs and buttocks and relieve pressure on the feet, reducing the risk of cramp. Laïka 16:16, 14 January 2008 (UTC)

9V battery on the tongue again...[edit]

Yes, we all know it tingles and maybe hurts a little bit - but what's the deal with that foul taste afterwards? --Kurt Shaped Box (talk) 12:44, 14 January 2008 (UTC)

Are the conditions they are made in very sanitory? I would guess it is just the taste of the metal. (Also did you have to go do this to discover this - be honest :) ). I think licking coins produces a similar taste without the electrocution. Lanfear's Bane | t 13:02, 14 January 2008 (UTC)
Didn't *have* to - but there's a lot of things that we don't strictly *have* to do when we're kids... ;) --Kurt Shaped Box (talk) 18:31, 14 January 2008 (UTC)
To be pedantic, it isn't electrocution when it does not result in death. Bovlb (talk) 21:16, 14 January 2008 (UTC)

With the voltage and whatnot, I wouldn't be surprised if some of the metal on the cathode/anode (forget which it would be) is oxidized, so that you could taste the metal ion. From a biological standpoint, I don't think it should be possible to taste neutral metal particles - they have to be charged, so that taste receptor proteins can detect the size and charge density of the ion.18.96.6.248 (talk) 14:04, 14 January 2008 (UTC)

FYI, it's a very similar taste to the one you experience when (purposefully or not) chewing on tinfoil. It's hard to describe - but it's a 'sharp' sort of taste. --Kurt Shaped Box (talk) 18:31, 14 January 2008 (UTC)
There are only five tastes that the human being can distinguish: sweet, sour, salt, bitter and umami. I suspect its not sweet, salt or umami, so that leaves sour or bitter (or a combination of the two). I suspect that the taste is caused by acids or alkalis being produced on the tongue. Now which of these tastes bitter or sour?--TreeSmiler (talk) 19:22, 14 January 2008 (UTC)
Ah Alkali tastes bitter and acid tastes sour. So now you know.--TreeSmiler (talk) 19:27, 14 January 2008 (UTC)

Insect maturbation and animal in general[edit]

Some time ago I saw an insect hovering in air for some time and ejecting some fluid after a while. Now seeing as insects should only expel feaces in semi-solid form, I concluded (with the help of the embarassed expression of my biology teacher when I asked her about it) that this insejt was masturbating(please correct me if I'm wrong). I wanted to ask which animals don't mastubate? And why?Bastard Soap (talk) 13:57, 14 January 2008 (UTC)

Our article on Animal sexual behaviour gives examples of similar behaviour in most species of mammal - it doesn't mention insects, but presumably there's nothing to stop them. Laïka 16:26, 14 January 2008 (UTC)
For some reason, I just can't imagine tortoises masturbating... --Kurt Shaped Box (talk) 02:19, 15 January 2008 (UTC)
  • I'm no biologist, but why can't insects expel liquid waste? --M@rēino 16:39, 14 January 2008 (UTC)
  • And some insects spit, saliva to digest, or nasty chemicals to kill or repell, and some have a sting with liquids to poison, and then some produce liquid silk to make a thread. There are many liquid possibilities. Graeme Bartlett (talk) 19:56, 14 January 2008 (UTC)
Female fish lays unfertilized eggs. Male fish expel sperms to fertilize them. Would you call this masturbation? NYCDA (talk) 22:33, 14 January 2008 (UTC)
No, I’d call it birth control. --S.dedalus (talk) 02:14, 15 January 2008 (UTC)
Yes. Yes I would. I hope that God is watching them too. --Kurt Shaped Box (talk) 02:15, 15 January 2008 (UTC)
The ceiling kitten is definitely watching them. --Dweller (talk) 15:20, 16 January 2008 (UTC)

Electrical question[edit]

Some time ago I was replacing an electrical socket and had a scary experience: I turned off the power at the switch box, verified that it was off by 1) hearing a radio that was plugged in go silent when I cut the power, and then 2) testing it with a doodad that lights up when you hold it near a power source, and then 3) by swatting the wires with the back of my finger: all negative. Then when I was wiring the new plug in, I happened to touch both wires with one hand and felt a definite tingling go through my fingers. I wasn't burned, and it scared more than hurt me. What could have caused this small amount of current to be going through the wires? A short circuit somewhere? Inductance? --Sean 14:47, 14 January 2008 (UTC)

It may have been stored charge - perhaps in a capacitor somewhere else in circuit, or even just in the wires; I've had a nasty shock from touching the live and neutral pins of an unplugged blender. Laïka 16:20, 14 January 2008 (UTC)
One possible reason is that some switch boxes only cut off the live wire. If the neutral is not properly earthed, you could still get a shock when touching the neutral wire and earth.--Shantavira|feed me 17:17, 14 January 2008 (UTC)
What country did this happen in? With proper house wiring in good condition, this could not happen in the US. You had a radio plugged in, so that would have bled away any mysterious phantom charge that might have impossibly been there. A length of non-coiled wire will not develop an appreciable induced voltage under any normal conditions; that would take a nuclear strike or a lightning bolt or something. If I were you, I'd make sure I had a good earth ground to the house, anyway. (If you get between the earth and the house, it can kill you if things aren't right, so let an electrician look at it.) Then I would check every connection in the house for good ground and correct wiring, both at the box and at the other end. Something is wrong. --Milkbreath (talk) 17:45, 14 January 2008 (UTC)
In the USA. The house is about 30 years old. I'm not the owner, but I'll let her know. Thanks, all. --Sean 19:15, 14 January 2008 (UTC)
I've seen Americal wiring and it scares me. DuncanHill (talk) 19:28, 14 January 2008 (UTC)
With regard to With proper house wiring in good condition, this could not happen in the US., I'm not so sure about that. There's at least one situation where you might be able to feel something: Imagine a cable that is carrying two different circuits fed from two different breakers. De-energize one circuit and work on it. The circuit is sufficiently isolated from power that there's no hazard, but capacitive coupling within the cable might put voltage (sourced from a high impedance) on the otherwise-open wires. This situation should be pretty rare, though. In the U.S., two circuits sharing a common neutral conductor are supposed to have their supply breakers mechanically-tied together so both are energized and de-energized together, but it's also allowed to have cable with two hots and two neutrals; this rare sort of cable doesn't require mechanical-tying of the supply breakers.
Atlant (talk) 19:42, 14 January 2008 (UTC)
Atlant, I dont think capacitive coupling at 60 Hz has any chance of creating a dangerous voltage unless you are talking miles of cable. No, the answer is clearly given in my earlier post just below: It is Common impedance coupling On which we dont seem to have an article.--TreeSmiler (talk) 21:18, 14 January 2008 (UTC)
Please note that I don't claim that a "dangerous" amount of current is available, only that a "sensible" amount could be present. And I think if you do the math, you'll reach the same conclusion that I did; 26 nF has a capacitive reactance of 100Kohms (that is, approaching dry skin resistance) at 60 Hz and it's not inconceivable that a cable might have capacitances approaching at least a few nF. And thanks to gadgets such as phase-control dimmers, power lines often have noise components at frequencies much higher than 60 Hz, reducing the amount of coupling capacitance needed to allow someone to "sense" something.
Atlant (talk) 14:15, 15 January 2008 (UTC)
Atlant, the capacitance of twin and earth cable used here is 100pF/m. I dont know where you got your figure of 26nF, but that would equate to a wire run of 260m of good old British cable. I know houses tend to be quite big in the US, but this sort of run is, shall we say, quite large. Assuming a more conservative run of, say 26m, this would give a capacitive reactance of about 1Megohm. At 120V rms this obviously gives 120uA rms through the body( neglecting the 700R or so internal resistance of the human being). According to PD6519 Part1:1988 [3] (an IEC/BSI document), body currents below 500uA usually have no reaction effect. Also dont forget that the neutral wire would probably be earthed at the distribution board AND the OP said he had removed the fuse for the circuit in question. Capacitance effects are therefore completely eliminated and the only possibility is that the neutral was elevated and he touched neutral and earth at the same time. However, the neutral would need to be elevated by more than about 50v for him to feel anything I think.--TreeSmiler (talk) 23:25, 15 January 2008 (UTC)
Addendum. After a bit of Goggling it appears that about 1 mA is the threshold sensitivity on the skin [4]--TreeSmiler (talk) 23:43, 15 January 2008 (UTC)
Whatever Google might say, I can detect currents much smaller than 100 microamps, possibly down to 10 microamps in some conditions. In my younger (and more foolish) days I used to experiment with the effects of different currents on skin, flesh and muscle. I don't advise anyone else to repeat my experiments - I didn't use mains voltage for the higher current tests! 3 mA is considered the safe limit anywhere near the heart, but it takes about 10 mA to stop muscles working. dbfirs 09:48, 19 January 2008 (UTC)
It is possible to get a small voltage between neutral and earth because there may be a small voltage drop across two end of a neutral wire passing a large current. This should not amount to more than a few volts and should not be enough to present a shock hazard. If you have received a tangible shock, then you should get the wiring checked out by a qualified electrician. Here lies the danger of DIY electrical work!--TreeSmiler (talk) 19:38, 14 January 2008 (UTC)
You probably felt a slight shock because appliances that were still connected to the line gave a feed back. Generators are motors in reverse. If you had a fan still connected and it was still turning, it would in effect become a generator. Any appliances could also be causing the feed back. Next time you replace a recepticle, connect a incadecent lamp to it. Confirm the light went out and wait a few more minutes for the light to drain the residual charge from the appliances. BTW TreeSmiler I think you mean inductive not impedance coupling. The chances of capacitive or inductive coupling is extremely remote to be case here. NYCDA (talk) 22:23, 14 January 2008 (UTC)
Yeah, that's true. A big fan spinning down would do that. So, it can happen a little. But I still don't like it, and I'd want to verify the cause. --Milkbreath (talk) 00:13, 15 January 2008 (UTC)
This is why utility workers say "It ain't dead til it's grounded." Perhaps somehow the switch killed the neutral instead of the hot phase. That would make the radio go dead but leave jolting voltage between the phase wire and the ground. The neutral to ground voltage is usually not all that high. I would bet that if you had checked it with a voltmeter you would have seen a steady voltage between conductors or between one of the conductors and ground of at least tens of volts. Perhaps there was a problem with grounding. Many power quality problems wind up being such. I doubt is was a motor winding down and acting as a generator. There could be a sneak circuit through another appliance which put some voltage on the phase conductor which you isolated from the mains by opening the breaker. Edison (talk) 03:34, 15 January 2008 (UTC)

Permanent Marker[edit]

Strange question but...Is the ink from permanet markers flammible? If I colour in something around a fire-place with permanent marker would it be liable to set on fire? —Preceding unsigned comment added by 194.221.133.226 (talk) 15:32, 14 January 2008 (UTC)

it shouldn't be flammable after having dried...18.96.6.248 (talk) 16:11, 14 January 2008 (UTC)
It depends what the something is. There are usually strict regulations about what materials can be used in a fire surround. Marker pen ink is unlikely to make it worse though (whereas some paints are flammable).--Shantavira|feed me 17:21, 14 January 2008 (UTC)

Feline Breeding[edit]

There is a void of information about becoming a cat breeder. For first timers it would be really helpful to have some solid information about the ins and outs of cat breeding. I've gleened some info and put it on my site, Alien Encounter Cattery but I cant find a single source for the intricacies of breeding, genetics, in-breeding and the actual physical labor involved with cat breeding in general. If there is anyone out there who could point me in the right direction and/or provide this info that would be great!

Sara —Preceding unsigned comment added by 63.200.184.126 (talk) 18:14, 14 January 2008 (UTC)

Where have you looked? Amazon, for example, have plenty of books on the subject, including such titles as The Complete Book of Cat Breeding, Breeding Pedigree Cats, Proven Marketing Tips for the Successful Cat Breeder, A Handbook of Pedigree Cat Breeding, Cat Breeding: A Complete Guide, and many more. I wouldn't expect to find much information on such a specialist subject for free on the Internet. It's not as though someone can usefully write just the odd webpage about it. Why would they when it's their livelihood?--Shantavira|feed me 17:22, 15 January 2008 (UTC)

Spice effects[edit]

Why do hot spices make people have runny noses and make people feel hot? How and why do hot spices cause those physiological effects in humans? —Lowellian (reply) 18:38, 14 January 2008 (UTC)

Gene synthesis[edit]

Is it possible to synthesize an arbitrary DNA sequence? As in, I send a document reading "AACGTACTACGATCGACTACGTGATC..." off to a lab and they return to me a sample of DNA with that sequence. If this is possible, how is it done? --Rannovania (talk) 19:47, 14 January 2008 (UTC)

Yes, you can read about it in Oligonucleotide synthesis. Someguy1221 (talk) 19:54, 14 January 2008 (UTC)
I do it all the time. You can order DNA primers from many biotech vendors. Invitrogen has some info in a FAQ that you might find useful. — Scientizzle 23:14, 14 January 2008 (UTC)

Blood Clot[edit]

question removed

The Wikipedia Reference Desk is not able to offer medical advice. Please consult your (or your mom's) physician or seek assistance from appropriate emergency medical services. Dragons flight (talk) 21:58, 14 January 2008 (UTC)

Question and replies re-removed. --Milkbreath (talk) 03:47, 15 January 2008 (UTC)

Diet Coke/Pepsi, ice, and foam[edit]

As part of a New Year's resolution to drop a few pounds, I recently switched to drinking only diet sodas (don't worry, I am exercising and have made other dietary-related changes). I couldn't help but notice that Diet Coke and Diet Pepsi seem to create MUCH more foam when added to a glass full of ice than their non-diet cousins. I have to wait much longer for the suds to die down before I can continue pouring very much at all in. Why would this be? I'm just curious. --24.147.69.31 (talk) 23:03, 14 January 2008 (UTC)

I don't have an answer, but I suspect that whatever the reason is, it's related to why the Mythbusters determined that Diet Coke was the ideal choice of drink for the Diet Coke and Mentos experiment. Confusing Manifestation(Say hi!) 01:31, 15 January 2008 (UTC)
Poke you finger into the foam. Works wonders. —Nricardo (talk) 01:44, 15 January 2008 (UTC)
I've been curious about the stability of foam is sodas as well. I've noticed that the foam produced when making an ice cream float with coke is extremely stable. I could leave it for minutes and a lot of it would still be there. I wonder if it has anything to do with the fat content of ice cream making a stable film. (I'm sorry for talking about coke floats in a diet related discussion by the way... :P Perhaps this can be attempted with sugar free ice cream and diet coke?) 152.3.44.183 (talk) 01:54, 16 January 2008 (UTC)

Ripply heat effect[edit]

What's the name for the effect when you can see the heat rising over something and it looks all ripply? Bellum et Pax (talk) 23:20, 14 January 2008 (UTC)

The basic physics involved is called refraction. I don't know if there is a name for the ripply effect per se, since that is just atmospheric refraction with turbulence. See also: mirage. Dragons flight (talk) 23:43, 14 January 2008 (UTC)
An astronomer would call it "really bad seeing". -- Coneslayer (talk) 01:31, 15 January 2008 (UTC)
It's called heat haze, but that just redirects to mirage. --Heron (talk) 19:24, 15 January 2008 (UTC)
Schlieren lines? DMacks (talk) 19:43, 15 January 2008 (UTC)