Wikipedia:Reference desk/Archives/Science/2008 November 12

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November 12

What shape is this?

I was thinking about this some time ago. Imagine a small room that has a door on each of its six faces. On the center is a flower pot and some clothes that I discarded. If I open and enter any of the doors in this room, I will enter a room with the flower pot and the same clothes that I discarded earlier. My question is, what is the shape of the room? I'm pretty sure it is not 3 dimensional. --Lenticel ^(talk) 00:37, 12 November 2008 (UTC)

I think you have been trapped in a game. In many old 2D games when you went off one side of the screen you reappeared at the other side. Obviously they have upgraded your game to ake advantage of a graphics processor to do 3D. On the other hand you might like to read the bit at the end of Shape of the Universe,we may be in something far weirder. 01:10, 12 November 2008 (UTC)

A room with 4 walls, a floor, and a ceiling could be considered as a cube with six faces. CBHA (talk) 02:43, 12 November 2008 (UTC)

This reminds me of a hemicube. Anyway, I'd say either the room is three dimensional, but the geometry isn't Euclidean, or you're on a three-dimensional analogue of a torus. That is, the surface is three-dimensional. — DanielLC 01:22, 12 November 2008 (UTC)

Topologically speaking, if the room has six walls in addition to floor and ceiling, the floor of the room could be a sphere, a torus, or a projective plane, for example. If it has four walls + floor and ceiling, then the room could be a three-torus or any number of weirder manifolds. Algebraist 01:31, 12 November 2008 (UTC)

Wow, this weirder than I thought. --Lenticel ^(talk) 01:37, 12 November 2008 (UTC)

We could narrow it down further if we knew whether or not going through any of the doors changes you from being right-handed to left-handed, or vice versa (or, equivalently, makes everything else in the room turn into its mirror image, but changing you sounds more fun!). --Tango (talk) 01:46, 12 November 2008 (UTC)

We also want to know whether going through a door changes your "up". —Tamfang (talk) 07:56, 14 November 2008 (UTC)

I wonder whether you got this idea from Cube 2: Hypercube which has similarities (but limited logic). PrimeHunter (talk) 01:56, 12 November 2008 (UTC)

Well I got the idea while I was taking a bath earlier today. The cramp bathroom inspired the idea. By the way, the movie seems to be cool. Maybe I'll try to find a DVD version later.--Lenticel ^(talk) 02:18, 12 November 2008 (UTC)

There are ten finite Euclidean 3-manifolds.[1] —Tamfang (talk) 05:25, 2 September 2023 (UTC)

If the answer is "not 3 dimensional", then the word you're looking for is "Hexagon". APL (talk) 14:03, 12 November 2008 (UTC)

It's not a tesseract is it? It's a non-3-dimensional shape which is connected in ways I don't understand. AlmostReadytoFly (talk) 16:35, 12 November 2008 (UTC)

A tesseract is 4D, I don't think we have any reason to believe we're working in 4 dimensions. --Tango (talk) 16:42, 12 November 2008 (UTC)

Potential Energy

For the sake of simplicity, let's consider gravity. Now I understand why the gravitational potential energy of an object has to be negative (as it approaches the source of gravity its potential energy must decrease in order to allow its kinetic energy to increase), but isn't energy the ability of an object to do work? And so it seems odd that an object could have negative energy (when its, say, lying on a table). How would one resolve this apparent contradiction? Thanks. —Preceding unsigned comment added by 76.69.241.185 (talk) 00:46, 12 November 2008 (UTC)

It doesn't have to be negative, you can set the zero of potential energy to be anywhere you like. The maths is often easier if you set the zero to be at infinite distance and thus have it always negative, but it doesn't really matter. All that matters is the change in energy. For an object on a table it would probably make sense to set the zero to be when the object is on the ground, since that's the lowest it can get. If you do that, then when it's on the table it has positive energy and can do work as you would expect. --Tango (talk) 01:04, 12 November 2008 (UTC)

For an object A in a gravitational field of another object B, it makes sense to define a zero of potential energy at very large (infinite) distance between the objects, and to measure the velocity relative to the center of mass (CM) of the system of the two objects. Then, if the TOTAL energy of A is negative, then it is on the bound orbit around CM ; and if the TOTAL energy of A is positive, then it is on the open orbit. Gravitational potential energy of A is always negative. If A performs work, its total energy decreases, but its instant potential and kinetic energy may either increase or decrease, provided their SUM (the total energy) decreases and provided the potential energy stays negative. Now, for the AVERAGE potential and kinetic energies of A in the BOUND orbit, you can apply a so-called virial theorem. For a classical gravitating system, it states that AVERAGE kinetic energy Ekin equals minus half the AVERAGE potential energy, Ekin = -Epot/2 ; or, equivalently, Etot = Ekin + Epot = -Ekin = Epot/2 < 0 . In a two-body system the AVERAGE is determined over a closed orbit; in a many-body gravitational system the strict average is over an infinite time, but for a "very large" finite time the result holds with high accuracy, too. Anyway, since E = Epot/2, body A performing work DE > 0 changes E to E - DE, so makes Epot "more negative" (thta is, larger in its absolute value). That means that Ekin also becomes larger in its absolute value! What happens is, the body A, having lost some energy, moves to a tighter orbit where its total energy is indeed lower (larger in absolute value, and negative) but its mean-square speed is higher. Hope this helps. --Dr Dima (talk) 01:47, 12 November 2008 (UTC)

Camera red eye and white eye

I've noticed that my new camera often causes people to have one red pupil and one white pupil instead of the standard camera red eye. I thought that the red eye was caused by reflection of the red on the back of the eye. So, that doesn't explain how the white eye effect is produced. It never happened with any of my older cameras. So, I am left wondering if it is the camera. Has anyone else here had a camera do this? Is there a fix to make it stop doing it? It is a pain because the auto-removal of red eye doesn't work if the pupil is white. -- kainaw™ 01:41, 12 November 2008 (UTC)

Could it be some weird anti-red eye feature going horribly wrong? Try turning off any weird anti-red eye features and see if it stops happening. --Tango (talk) 01:50, 12 November 2008 (UTC)

Also, have you tried it with different subjects? Maybe the person you are photographing has a strange eye (in which case, they should probably see a doctor!). --Tango (talk) 01:51, 12 November 2008 (UTC)

I have noticed it with more than one person. About 90% of the times I've seen are with my son. But, about 99% of the photos I take are of him. So, there is no reason to think he is more prone to it. I've tried to turn off all weird functions on the camera. It isn't easy to use because it is designed to be so easy to use that it decides what you want and does it for you - refusing to let you decide what you want. Something I did got it to stop blinking the flash 4-5 times before snapping a photo - which often meant that the cool photo of my son would end up being him covering his eyes and turning away from the evil flashing light. -- kainaw™ 02:08, 12 November 2008 (UTC)

This site has any explanation of camera red eye and one reason for white eyes: [2] Rmhermen (talk) 02:11, 12 November 2008 (UTC)

Thanks. It commented on the reflection being common when the pupil is angled away from the camera, towards the nose. Looking back at the photos I didn't manually correct, I can see that the people with one white eye are looking away from the camera and towards their nose. -- kainaw™ 02:40, 12 November 2008 (UTC)

I suppose it's worth asking whether your son is cross-eyed? If the two eyes were not pointing in the same direction - then the reflection off the retina of one, would not occur on the other eye. It's hard to imagine any other reason. SteveBaker (talk) 04:41, 12 November 2008 (UTC)

It's also possible if the camera is close to the person's face, but they're looking at something well behind the camera. I don't know how close the camera would need to be for this. --67.185.190.46 (talk) 06:36, 12 November 2008 (UTC)

My understanding is that if the eye is looking straight at the camera the flash will produce a reflection of the vascular, and thus red, back of the retina. However if the eye is not directly aligned with the camera the reflection is of the less vascular parts of the retina producing a white reflection. I believe the phenomenon of 'red-eye' is a human problem associated with the particular vascular anatomy of the human retina. Perhaps it occurs in other primates. Richard Avery (talk) 08:13, 12 November 2008 (UTC)

Since this is occurring with photos of several people, a medical cause is unlikely. However retinoblastoma can give this appearance. Axl ¤ [Talk] 12:05, 12 November 2008 (UTC)

Now that I had some search terms for Google (thanks), I understand. This happens with children and isn't very uncommon. If a child is looking away from the camera (by about 15 degrees), the eye that is looking towards the nose will turn white. The other will be dim red - not a complete red-eye, but not white either. If you look at eye, you can see the main optic nerve is not dead center in the back of the eye. It is about 15 degrees off center. So, if the child is looking away at just the right angle, you get reflection off the optic nerve, not the nice red part of the eye. Further explanation that I've found from tons of Google hits is that this is limited to children because the size of the whitish area around the optic nerve is larger in relation to the size of the eye than it is in adults. Also, adults tend to look at the camera, not slightly away - so they don't even get in position for this sort of reflection. Since I've been mainly photographing my 1-year old son and his friends, I've been picking up a lot of kids at just the right angle to get the white-eye reflection. -- kainaw™ 13:41, 12 November 2008 (UTC)

Light Has Intelligence?

I saw a "documentary" recently in which a "scientist" stated that light has shown to anticipate experiments in which it is involved. The guy did not seem like a crack pot. What in the world could he be referring to? —Preceding unsigned comment added by 75.67.217.220 (talk) 01:52, 12 November 2008 (UTC)

Perhaps retrocausality? Jkasd 02:16, 12 November 2008 (UTC)

See also, freebasing and crack cocaine. Plasticup ^T/C 02:50, 12 November 2008 (UTC)

I suspect you're thinking of things like the "wave-particle duality" effect and quantum mechanics. Because of the wave–particle duality of light, the results of certain experiments seem to depend on how you are measuring the results - which leads one to kinda imagine that the light in the experiment "knew" how you were ultimately going to measure it - and changed it's behavior beforehand.

I recommend reading Double-slit experiment - and Quantum eraser experiment.

Suffice to say, the light isn't "intelligent" - but it does behave in ways that seem so far from our normal experience that it's almost impossible to get your head around the implications. This stuff leads us into the ideas of parallel universes and all manner of other weirdnesses.

SteveBaker (talk) 04:37, 12 November 2008 (UTC)

I'd guess the Elitzur-Vaidman bomb-tester is closest to what he might have been thinking of Dmcq (talk) 09:04, 12 November 2008 (UTC)

The deal with light is that it is not a particle or a wave, it is its own thing. Its just "light". We have models that treat it like a particle; and those models work to explain some of the behaviors of light. We also have models that treat it like a wave; and those models work to explain some of the behaviors of light. The deal is, that both models fall apart roughly 50% of the time; that is for any set of conditions in which light behaves as a particle, the wave model looks like it doesn't work, and visa-versa. The reality of light is that it doesn't have an analog in the "big" world. You can't say light is like _blank_, where _blank_ is any thing you have the ability to manipulate with your hands. Any "contradictions" in lights behavior, which make it, for example, appear "intelligent" as described (such as the aforementioned Double-slit experiment), are just the result of the faultiness of our models. Its our problem, not light's... --Jayron32.talk.contribs 17:24, 12 November 2008 (UTC)

The trouble is that this is simultaneously a correct - but also intensely frustrating - answer! You're absolutely right - light is something for which we have no analogs - which leaves us no way to explain it that does not tempt us into dangerous extrapolation-from-experience. Ordinary 'stuff' has a mass and you can stop it moving. Then you can stick it on a weighing machine and you know it's mass. When you push ordinary stuff towards light-speed, it gets heavier and heavier - and if you could somehow get it up to light speed, it's mass would be infinite. So the mass of normal 'stuff' is infinite at the speed of light and something reasonable all the rest of the time. Photons, however can only move at the speed of light - but yet they have actual sane, finite masses. Time is similarly warped - so for the photon, time doesn't exist...neither does distance. It's no wonder that it 'misbehaves' in every way imaginable compared to normal 'stuff'. The very nature of the zeroes and infinities that pop up at the speed of light in relativistic calculations pretty much guarantees that light is going to be weird. SteveBaker (talk) 22:05, 12 November 2008 (UTC)

How come garbage explodes only when it's buried?

The old lady told me to take out the garbage earlier (always naggin') so I jokingly said I'll chuck it in the backyard. Then she said "You can't throw it in the backyard, ass-h*le, it'll draw rats!" Then I said, "Fine, I'll bury it! That way I wont have to pay a goddam garbage bill!" Many colorful obscenities later she told me that garbage will explode if buried for a short time. I didnt want to agree with her at the time, but I vaguely remember hearing that's why landfills are vented and have flames shootin out of factory whistle lookin thingamajigs. My neighbor 3 trailers down has had garbage all over his yard for years that wasnt buried and he hasnt had no problems. Not even rats. What gives?Sunburned Baby (talk) 02:28, 12 November 2008 (UTC)

Maybe it explodes on Wednesdays while your friend is at work? —Preceding unsigned comment added by 83.199.126.76 (talk) 02:32, 12 November 2008 (UTC)

Much of our garbage tends to produce methane when it decomposes. When sitting in the open, the gas just floats away. When buried, it builds up in pockets. If, for some reason, the pocket of gas is ignited, it can make a small explosion. Venting natural gas from landfills isn't done just for safety. There are people who buy natural gas, so the landfill companies bottle up the byproduct for profit. So, why not bury your garbage, stick a hose down in it, and funnel off the gas into some empty wine boxes you have laying around. You might make enough to pay for a whole week's worth of lottery tickets. -- kainaw™ 03:06, 12 November 2008 (UTC)

The "some reason" for the gas igniting Kainaw mentioned is often an exothermic reaction in the decomposition process. I tried to find a nice link for you. Although several sites including our Composting page mention the fact that decomposition by anerobic bacteria generates heat, I've failed to find a nice concise description of the process. Anaerobic respiration holds some clues, but not much context. What you get is spontaneous combustion which has a dead end link to Fermentation (biochemistry). Don't get you hopes up for not getting rats when you bury the stuff. I used to live next to a former dump and the critters had no problem burrowing to the larder. You'd just get a chance to ignore what you don't see. Your neighbor who didn't get any might have had a local ecosystem (e.g. snakes, cats, owls etc.) that kept the rat population down to an unnoticeable/non existent size. The amount of biogas you get out of your household waste is not likely to reach marketable amounts unless you wish to build a Mount Trashmore in your back yard. The volume of easily digestible biomass in proportion to stuff that takes decades to break down is likely not very high. To reduce the volume of trash you put out you could deliver glass, plastics, metals and paper to a local recycling center and pepper your back yard with compost barrels (no access for rats) to use the compostable portion of your biodegradable trash. Depending on gas prices and local garbage collection policies and prices you might come out ahead or not. 76.97.245.5 (talk) 07:17, 12 November 2008 (UTC)

This begs the question of why Mount Trashmore doesn't explode? Let's see those skaters jump that one!Sunburned Baby (talk) 03:02, 16 November 2008 (UTC)

Methane as cause of global warming

Im looking for references that Methane in the atmosphere causes much more global warming than co2 and therefore that burning natural gas is good for the earth.--GreenSpigot (talk) 02:58, 12 November 2008 (UTC)

Woooaahh...be very VERY careful how you say that!!

Our Methane article does indeed say (correctly) that "Methane is a relatively potent greenhouse gas with a high global warming potential of 72 (averaged over 20 years) or 25 (averaged over 100 years)." (and there is a reference for that). CO2 has a 'global warming potential' of 1 - so clearly Methane in the atmosphere is a REALLY bad thing.

HOWEVER it is most certainly NOT a good idea to drill for natural gas and burn it in order to save the planet! It's far better to leave it underground where it belongs! Methane deep underground where it's been safely buried for millions of years - is just fine where it is! The only (exceedingly special) time when what you say is correct is if the natural gas is already in the atmosphere - then converting it to CO2 is better than waiting for many decades for it to degrade by itself.

So please don't go around saying "we should all be using natural gas because it's good for the atmosphere" - because nothing could be further from the truth! The kinds of situation we're talking about is when (for example) you have a herd of dairy cows and their poop would normally produce a bunch of methane that would do terrible things to the planet - then it is much better to use that methane as a fuel (both extracting some useful energy - and converting it into much safer CO2 in the process).

SteveBaker (talk) 04:22, 12 November 2008 (UTC)

Methane is more potent per molecule; however, in absolute terms we've added much more CO2 to the atmosphere than methane, so methane has had less of a global warming impact than co2. Dragons flight (talk) 05:53, 12 November 2008 (UTC)

Yes - I agree. This may change as the methane clathrate deposits in the deep oceans begin to melt. There has been some evidence that this exceedingly nasty situation is starting to occur - and (reluctantly) one has to say that burning the stuff as fuel (converting it to CO2) before it can ramp up the greenhouse effect (with the potency of methane) might be a last-ditch way to survive that situation. However, it's a decidedly "non-trivial" problem to do that - and we'd want to be very sure that the runaway melting of these deposits was really going to happen before we took such a drastic step. SteveBaker (talk) 14:57, 12 November 2008 (UTC)

Full moon on birthdays

Over the course of a lifetime of, say, 85 years, how often could one expect their birthday to coincide with the full moon? -- JackofOz (talk) 05:34, 12 November 2008 (UTC)

Three times on average. Dragons flight (talk) 05:54, 12 November 2008 (UTC)

Thanks. How did you work that out? -- JackofOz (talk) 07:29, 12 November 2008 (UTC)

A full moon occurs once every 29.5 days according to its article, so a birthday has one chance in 29.5 of coinciding with one. 85 is almost three times 29.5. (Something for werewolves to look forward to?) Clarityfiend (talk) 07:58, 12 November 2008 (UTC)

Yep, that's what I originally figured. It just felt way too low, so I thought I must have gone wrong somewhere. Depending on where the birthday falls, you might only manage 2 birthday full moons in an 85-year lifetime. Is there any way to work out, for any particular birthday and a given starting year, when the birthday full moons will occur, or do you have to use an ephemeris and do it "manually"? -- JackofOz (talk) 08:22, 12 November 2008 (UTC)

It probably sounds low because the moon changes size quite slowly and appears full to the naked eye (at least mine) for several nights a month. Algebraist 08:25, 12 November 2008 (UTC)

You probably would need an ephemeris; the 29.5 days varies a bit. However, there may be astrological software that can tell you when a solar return (birthday) coincides with a sun-moon opposition (full moon). You would also need to know the place of birth so that you could reduce the time to UT, the time used in most ephemerides.--Shantavira|^{feed me} 08:43, 12 November 2008 (UTC)

Pneumonia

What is the survival rate for untreated bacterial pneumonia if the victim is an otherwise-healthy young adult? --67.185.190.46 (talk) 06:28, 12 November 2008 (UTC)

Untreated, bacterial pneumonia kills ~30% of the afflicted [3]. Dragons flight (talk) 06:45, 12 November 2008 (UTC)

But it's occurrence and observation is, I assume, much higher in the sick and elderly. Being in good physical condition and having a robust immune system bacterial pneumonia may manifest itself as only a cough and I may not even go to the doctor. Any measurements (short of those from controlled experiments) is going to suffer monstrous selection bias. Plasticup ^T/C 15:05, 12 November 2008 (UTC)

Pneumonia describes an illness that necessarily has certain symptoms, i.e. fluid in the lungs, almost always accompanied by fever and some degree of difficulty breathing. If you only have a cough, then you might have an infection, but you do not have pneumonia. Dragons flight (talk) 16:22, 12 November 2008 (UTC)

It's certainly possible that a person whose only symptom is a cough has pneumonia. It's especially possible in the elderly or others with immune dysfunction, but not what you'd expect in the young: I think Darongs flight's point is that those with vigorous immune responses fight off infection before it becomes pneumonia. Since the question asks specifically about the young, we can't give a reasonable answer if the population studied includes the elderly and we don't have the data to correct for age. 30% is certainly high for a young population. - Nunh-huh 17:26, 12 November 2008 (UTC)

Lots of folks (especially kids) get so called walking pneumonia, otherwise identified as atypical pneumonia, often with mycoplasma as the causative agent. As a result of the slow growth rate of this organism, a generally healthy patient can exhibit nothing more than a nagging cough and certain degree of lethargy as they go about their daily business, which doesn't clear up after a long period of time. Most parents I know (who are reasonably frequent consumers of healthcare) are quite familiar with it. I'm not sure how it resolves itself if untreated, what I see is parents who see those symptoms in their kid for a couple of weeks, go to the doc and get the diagnosis, and get it treated with specific antibiotics. But if you're the type of person who avoids doctors unless absolutely necessary, for whatever reason, you probably wouldn't be worried enough to seek attention.Gzuckier (talk) 17:45, 12 November 2008 (UTC)

Query about today's featured picture.

What a fantastic picture, but that apart can anyone explain the blue/green light circle at the rotor tips. I understand that it is caused by lights but what is the purpose of the lights, surely they are not decorative. Are they part of some safety system that shows the position of the rotors at night to prevent..um.. unpleasant accidents? Richard Avery (talk) 08:23, 12 November 2008 (UTC)

Link to the image. Just in case this will not be answered today.--Lenticel ^(talk) 09:32, 12 November 2008 (UTC)

That's definitely an amazing photograph! This pdf linked from the V-22 Osprey talk page mentions "upgrading rotor tip lights & formation lights for improved night vision goggle (NVG) compatibility" and this page also mentions that the "prop-rotors have lights in the rotor tips for night safety." --LarryMac | Talk 14:23, 12 November 2008 (UTC)

See these pictures 1 and 2 of the B-25 Mitchell, an American bomber during the Second World War: it's long been a common practice to have something light at the edges of blades, although as you can see, 60+ years ago they simply painted the propellor tips rather than having lights at the edge. Nyttend (talk) 14:42, 12 November 2008 (UTC)

Certainly it's so that the pilot can visualise where the rotor tips are - that's especially important in this aircraft because it's a tilt-rotor craft - those engine nacelles swivel through roughly 90 degrees between hovering and forward flight. When hovering in confined areas - it's really useful to be able to see that your rotor tip is just about to whack into a tree limb or a lighting pole or something. I strongly suspect that they only turn them on in those specific circumstances because military aircraft don't generally want to be seen at night. SteveBaker (talk) 14:50, 12 November 2008 (UTC)

Thanks guys and gals, kind of what I thought but you have collectively sourced and expressed it so well. Richard Avery (talk) 15:21, 12 November 2008 (UTC)

Mars

How long could an unprotected human survive on the surface of Mars? —Preceding unsigned comment added by 195.188.208.251 (talk) 12:35, 12 November 2008 (UTC)

According to drowning, lack of oxygen takes about six minutes to cause brain death, so at most that long. I think that'll kill you before the cold does, but I don't know for sure. Algebraist 12:57, 12 November 2008 (UTC)

I'm not sure drowning is a fair comparison.

In any case the article on Time of Useful Consciousness, says for altitudes over 50,000ft, you've only got 9 to 12 seconds before you lose the capacity for rational thought. The surface of Mars would be similar or worse. So, you'd want to get back inside pretty quickly. APL (talk) 13:59, 12 November 2008 (UTC)

The atmospheric pressure on the surface of Mars is a shade less than one percent of the air pressure at Earth's sea level. For the purposes of sustaining life, it's better described as a low-quality vacuum than an atmosphere. In that vein, you'll probably be interested in our articles on the Armstrong limit, Human adaptation to space#Unprotected effects, and space exposure. Briefly, you would expect somewhere in the neighbourhood of 10 seconds of useful consciousness. Based on animal experiments, if your friends dragged you into the airlock and repressurized you within about 90 seconds, you'd probably survive without permanent injury. Beyond that threshold, you're probably toast. (I would expect rapid, serious damage to the lungs.) TenOfAllTrades(talk) 15:53, 12 November 2008 (UTC)

What would cause that damage? If you survive the initial decompression (most importantly, don't try and hold your breath), the barotrauma from a difference of (effectively) one atmosphere shouldn't be too extreme. I think it's hypoxia that would kill you by damaging the brain (it important to note that hypoxia is worse in hard vacuum than when drowning - the oxygen is kind of sucked out of you rather than just being used up, hence 90 seconds rather than the 6 minutes Algebraist mentioned). Since the Martian atmosphere isn't much of a thermal conductor (there simply isn't enough of it), the cold would take longer to affect you so we can probably ignore it. --Tango (talk) 16:10, 12 November 2008 (UTC)

From Space exposure : "But severe symptoms such as loss of oxygen in tissue (anoxia) and multiplicative increase of body volume occur within 10 seconds, followed by circulatory failure and flaccid paralysis in about 30 seconds.[1] The lungs also collapse (atelectasis) in this process, but will continue to release water vapour leading to cooling and ice formation in the respiratory tract." APL (talk) 22:13, 12 November 2008 (UTC)

Leaves changing color at different rates

Here in Beaver Falls, Pennsylvania, most leaves have fallen, but there's a large maple with large leaves (I'm guessing Norway Maple) behind my house. Reading Autumn leaf color, I note that the article says that "Often the veins will still be green after the tissues between them have almost completely changed color." However, this tree is odd, with leaves that are more extreme than this: some of its leaves are totally yellow, while leaves farther up the branch are almost totally green still. Is it simply because these leaves are closer to the trunk, or because they're (most of the time) shaded by the leaves at the edge of the tree, or some other reason? And is this an unusual phenomenon, or is it common and I've really not been paying attention all my life? I checked last night, by the way: they really are on the same branch, so it's not as if there are leaves from two trees intermingled. Nyttend (talk) 14:36, 12 November 2008 (UTC)

Leaves change color because the sap is "running", as they say in the maple sugaring industry. Basically, all of the sap (i.e. sugary water) is drained out of the tree into storage in the roots. This makes sense because the roots are insulated by the ground, where as the leaves are basically big heat-dissipators, and so are VERY suceptible to freezing. The process is relatively slow; it can take several days to weeks to complete, depending on the size of the tree. For very large trees, the leaves at the periphery (i.e. farthest from the trunk) are "drained" first, so the leaves there die off earlier. For very large trees, the leaves at the tippy-top can have changed and fallen before those near the bottom and close to the trunk have even begun to start changing. --Jayron32.talk.contribs 17:37, 12 November 2008 (UTC)

Not sure where there's stuff about this but the colour in those leaves is put there to protect the leaf from sunlight whilst the tree absorbs back anything useful. Putting in that golden colour costs the tree. So the outermost leaves and those facing south will be coloured most. You might notice leaf buds are often brown or red too to protect them whilst developing. Dmcq (talk) 18:02, 12 November 2008 (UTC)

human fat

in Volume how does a pound of human fat compere to lard —Preceding unsigned comment added by Seanbaguley (talk • contribs) 15:30, 12 November 2008 (UTC)

Both are slightly more than 0.9g/c^3, a little less than water. Lard is slightly denser. SDY (talk) 15:35, 12 November 2008 (UTC)

length of Vibrio cholerae

What's the typical size, i.e. length of a cholera bacterium? --Ayacop (talk) 16:21, 12 November 2008 (UTC)

2-3 microns in length, 0.5 microns in width. - Nunh-huh 17:15, 12 November 2008 (UTC)

Could you add that to the article Vibrio cholerae? Rmhermen (talk) 23:18, 12 November 2008 (UTC)

yeast need salt?

In order for yeast dough to rise does it need to contain salt? RJFJR (talk) 17:04, 12 November 2008 (UTC)

No. See fermentation. 93.132.179.55 (talk) 17:14, 12 November 2008 (UTC)

Salt is used in baking to control the rate of fermentation, but is not strictly necessary for fermentation proper. However, "without salt, the yeast acts very rapidly and peters out too quickly. Too much salt will stunt yeast activity" [4]. "Salt controls yeast activity to achieve a slow, steady rise and it strengthens the dough structure; eliminating salt can result in a baked bread that has collapsed." [5] - Nunh-huh 17:17, 12 November 2008 (UTC)

Thank you! RJFJR (talk) 18:22, 12 November 2008 (UTC)

Just as an aside, bread made with no salt tastes terrible. Robinh 21:53, 12 November 2008 (UTC)

The Tuscans would probably disagree with you. (Classic Tuscan bread is made without salt.) -- 128.104.112.72 (talk) 23:32, 13 November 2008 (UTC)

Strength difference men-woman

What is the strength difference between men and woman?--Mr.K. (talk) 18:52, 12 November 2008 (UTC)

Estimates vary, particularly based on how you define "strength". this USMC report suggests the average woman's strength is 40%-70% of her male counterpart's. This report (with a higher average age) notes 50%, and then proceeds to note that males are also heavier and that strength-per-weight (if you elect to use that sort of "strength" definition) has a completely different result -- they find that males and females are effectively equal in terms of strength-per-muscle-mass. — Lomn 19:41, 12 November 2008 (UTC)

No surprise there, though, right? I don't think it's headline news to announce that folks with bigger muscles tend to be stronger... Matt Deres (talk) 17:29, 13 November 2008 (UTC)

Animal abuse

Wikipedia is preventing me from linking directly to the image I'm talking about. But on that site, encyclopedia dramatica, when you search "Animal Abuse", at the bottom you see an animated gif of a cat in some terrible device that shoots some liquid from the bottom into a chamber that the cat is in. What is that device that the poor cat is in? 98.221.85.188 (talk) 21:06, 12 November 2008 (UTC)

Encyclopedia dramatica is basically a joke site; I would not judge anything I read there too seriously. --Jayron32.talk.contribs 21:12, 12 November 2008 (UTC)

The Pet Spa [6]. Hydromassage, bath, and blowdry machine for dogs and cats. Edison (talk) 21:23, 12 November 2008 (UTC)

That's kind of a relief. But why was the cat so upset when it was in there? Was the water too hot? Was the machine being misused? 98.221.85.188 (talk) 22:04, 12 November 2008 (UTC)

Most house cats can't stand getting their fur wet. There are exceptions to this rule, of course, but I have a hard time imagining your average house cat enjoying a "hydromassage". APL (talk) 22:09, 12 November 2008 (UTC)

What's the problem with linking to encyclopediadramatica? —Preceding unsigned comment added by 83.199.126.76 (talk) 21:51, 12 November 2008 (UTC)

If I'm reading the spam black and whitelists right, you can't link anywhere on ED except the Main Page, because (a) it's a haven for anti-Wikipedia trolls, and (b) it's a haven for trolls in general, and has tended to be linked only to harass someone or to act as a shock site. I may be wrong, but I suspect Main Page was whitelisted only after the actual article on the site finally passed its 1000th deletion review. Confusing Manifestation(Say hi!) 22:33, 12 November 2008 (UTC)

Why is 350°F the standard for cooking food?

Almost every recipe I see wants to be cooked in an oven that is 350°F. Some call for temps up to 450°F. But I've never seen any recipe that calls for a temp outside of these extremes. (I'm sure there are exceptions) What's so special about this temperature range and cooking food? --70.167.58.6 (talk) 22:21, 12 November 2008 (UTC)

Related article or place to start deduction from: Temperature (meat). Mac Davis (talk) 22:30, 12 November 2008 (UTC)

Actually, that article doesn't help.

I think the temperature has more to do with the smoke point or flash point of fats and oils. Lard, for example, has a smoke point of about 370°F. Vegetable shortening smokes around 360°F. You don't want all the fat burning away while the food cooks.

Higher temperatures are useful for different cooking techniques, such as searing the outside of a piece of meat so that the inside continues to cook after it is removed from the oven. ~Amatulić (talk) 22:48, 12 November 2008 (UTC)

Note the temperatures in the Temperature (meat) article are the meat temperatures when cooked, not the oven temperatures.

When oven cooking foods of any significant thickness (such as cakes, pies, roasts of meat, puddings, large potatoes) using too low a temperature will not cook them through to the middle, or will take an unnecessarily long time to do so. Using too high a temperature is likely to result in the outside being dried out or burnt before the centre is cooked. The recommended temperatures are compromises between these two problems. CBHA (talk) 23:04, 12 November 2008 (UTC)

If you'd like to use different temperature settings, try a convection oven. NB Acrylamide is produced in increasing amounts at temperatures exceeding 350 F. The temperature settings of ovens are not a reliable indicator of actual temperatures inside (and those tend to vary significantly from one point in your oven to the other). You may find recipes for conventional ovens that tell you on what rack / distance from the heating element to place your food. To be sure your food is cooked properly use a meat thermometer. To make sure baked goods are done, the traditional method is to stick a knitting needle in and declare it done when no dough sticks to the needle anymore. (OR by my granny :-) 76.97.245.5 (talk) 00:26, 13 November 2008 (UTC)

Generally, 350 deg F is a temperature which is hot enough to encourage the Maillard reaction to occur (aka "browning"), without causing substantial burning to also occur. If you get up into the 500 deg F range, the food will char or burn (i.e. produce ash) which imparts a bitter and unpalatable flavor. Below probably 325-350 deg F, and there is likely not enough heat for the vital Maillard reactions to occur; it's these reactions that produce those brown tasty bits that form when meat is properly cooked. Its also why most slow-cooking methods, such as "crock-pot" cooking, require you to brown the meat seperately before adding to the crock pot. The crock pot gets hot enough to cook the meat (generally up to around 180-190) but never gets hot enough to brown it; which means you miss an entire flavor component of the food. --Jayron32.talk.contribs 03:15, 13 November 2008 (UTC)