Wikipedia:Reference desk/Archives/Science/2007 May 15

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May 15

Can anyone identify this bird?

I took this picture of a dead hummingbird today. I know it's pretty low quality; but the number of hummingbird species that don't have images on Commons is staggering and I thought if anyone could identify it maybe it'd be useful someplace. So, does anyone know what kind of hummingbird this is? The picture was taken on the street in downtown Indianapolis. The bird is under a Honey locust tree. The nearest flowers are some Pansys in a pot on the corner. ~ ONUnicorn^{(Talk|Contribs)}problem solving 00:39, 15 May 2007 (UTC)

Realistically, I don't think there's any chance of a definite ID from that photo and it won't really be any use for illustrating articles. Maybe if you'd gone (much) closer with the camera... but at that level of detail it's not even very clear that it's a hummingbird. Sorry. --YFB ¿ 01:08, 15 May 2007 (UTC)

To add to that, for your own interest, a quick google suggests that it's likely to be a female Rufous hummingbird or Ruby-throated hummingbird, as they're the species with roughly this colouration most often found in Indiana. The female Rufous is near-enough indistinguishable from Allen's hummingbird, but there's no confirmed records of them in Indiana, although that could just mean nobody picked them out from the Rufouses. Cheers, --YFB ¿ 01:16, 15 May 2007 (UTC)

I'm pretty sure it wasn't a Ruby-throated hummingbird, and I don't think it was a Rufous hummingbird either. I've seen quite a few Ruby-throated, and even the females have more color then the dead bird in the photograph. Fewer Rufous visit my feeder, but I think the females of that species are sort of brown, aren't they? This one was pretty black-and-white, rather than drab brown. I know my keychain camera is shoddy, especially at close up, but while it looks like it could be blown highlights on the birds chest the feathers were white there. The bird caught my interest for a couple of reasons; first its location (no flowers around to speak of - and I hadn't seen hummingbirds downtown except by the canal and the state park), and second that I didn't recognize it as looking like hummingbirds that visit my feeders. Oh well. Thanks for trying. ~ ONUnicorn^{(Talk|Contribs)}problem solving 02:31, 15 May 2007 (UTC)

You may be right - I have zero hummingbird experience as I live in the UK. I've just had a look in my National Geographic Field Guide to the Birds of North America and I'm inclined to think it's an immature female ruby-throated. Based on location and markings, it's pretty unlikely to be anything else, as far as I can see. That would give it a whitish underside and throat, greenish-dark upperparts, probably less colour than an adult bird. Next time, try and get a closer photo! :-) --YFB ¿ 04:15, 15 May 2007 (UTC)

I hadn't thought about it maybe being imature... this time of year that's a good possibility. ~ ONUnicorn^{(Talk|Contribs)}problem solving 16:03, 15 May 2007 (UTC)

Can anyone explain me The mechanism by which sound wave propagates through air ?

interactive external links are welcome . —The preceding unsigned comment was added by 202.56.7.130 (talk) 01:52, 15 May 2007 (UTC).

Is our article on sound of interest? Splintercellguy 02:06, 15 May 2007 (UTC)

From looking at it, the article on sound isn't quite so helpful in explaining the propagation of the sound wave, but there's a bit of useful info in the article on longitudinal waves, of which sound is an example (and the external links look pretty handy, too). Confusing Manifestation 02:09, 15 May 2007 (UTC)

Sound waves are compression waves, they move through the air by quickly compressing and decompressing the surrounding molecules. Human ears are evolved to recognize certain frequencies of these compression waves as "sound". - 2-16 12:29, 16 May 2007 (UTC)

what is the aspect ratio of a normal human eye ??

Many computers monitors have a 4:3 but some, but some monitors have others, the aspect ratio of a cinema screen is not 4:3 is another one..... And the aspect ratio of your eyes what is what aspcect ration we see?? —The preceding unsigned comment was added by 201.8.100.1 (talk) 02:48, 15 May 2007 (UTC).

I don't think the concept of aspect ratio is applicable to the eye. Splintercellguy 03:07, 15 May 2007 (UTC)

Since the human visual field is circular, I suppose you could call the aspect ratio "1"; i.e. x = y. -- MarcoTolo 03:16, 15 May 2007 (UTC)

Conducting a little OR by staring at a wall and holding up my hands, it appears that, without moving my pupils, roughly 2/3 of the field of view of one eye is visible to the other. Head-mounted display says that the standard human interpupillary distance is 2.5-3", and visual field says that each eye can see -90° to +35°. I have seen standards for maximum recommended line length to make web pages comfortable, but I am not sure that that translates into any "most natural" aspect ratio. The fovea gives good detail and colour vision in the central 2° - taking a interpupillary distance of 7 mm and looking straight ahead, the fields of view of both fovea meet at a distance of one meter. Meaning that at that distance, the aspect ratio of your "good" vision will be 2:1 (as two tangent circles, not a rectangle), and closer in it would be two non-intersecting circles. Eldereft 04:40, 15 May 2007 (UTC)

OR: I measured the distance between the furvest points I can see to either side of, above and below my head, and it appears that my vision is an oval with a ratio of 8:3. but I expect this was distorted by the fact that I can see slightly backwards out of the very edges of my eyes. So I will see if I can find a better way to work this out.

I think I have worked out now that it is about 5:4, which seems a bit more likely. But in a way this is subjective. Maybe someone can work out an official test to see what shape we see.

The question has many answers, since the human visual system is very complex compared to a motion picture projection system, television display, or computer monitor. The human visual system includes in the retina a fovea, the area of most distinct vision, about 1 degree of visual field across, where cones, the receptors for color and for daytime vision, are most highly concentrated. This is smaller than the size of the thumb at arm's length and larger than the image of the moon. On a computer screen this is only a word or two wide at normal viewing distance. This foveal area of distinct vision is used to see by a sequence of largely automatic saccades or eyemovements, occurring several times a second, which are used to examine and analyze the visual environment. The area of distinct vision for a given fixation varies sightly between indivisuals, but is slightly wider horizontally than visually. Outside the area of distinct vision is an area which detects general shape and color and movement. [1] states that the binocular visual field (including less distinct vision) is 200 deg (w) x 135 deg (h), which sounds like an aspect ratio of 1.48. That source states that the area where the vision from the two eyes overlaps is 120 deg (w) x 135 deg (h), which would be an aspect ratio of 0.89 for actual stereoscopic vision. But in practice we look at something by moving the eyes in a sequence of saccades, and by moving the head when necessary, so the aspect ratio of vision is undefined. Edison 14:36, 15 May 2007 (UTC)

voltage

Suppose the reading on a voltmeter was "12 V". What would that mean, specifically? —The preceding unsigned comment was added by 68.20.221.168 (talk) 03:28, 15 May 2007 (UTC).

Well, it would mean that the potential difference between wherever the voltmeter probes have been placed is 12 volts. Also see the voltage article. -- MarcoTolo 03:48, 15 May 2007 (UTC)

There's also meter loading to consider (some current flows through the voltmeter), though it will probably be insignificant. If, for example, the impedance you place in shunt with the voltmeter probes is comparable to the internal resistance of the meter, connecting the meter will significantly alter the potential drop. The assumption that the meter reading accurately reflects the (unloaded) potential drop is valid if the internal resistance of the meter (typically a few megaohms) is much higher than the impedance over which the voltage is measured. -- mattb 01:22, 16 May 2007 (UTC)

Your car battery has a reasonable state of charge? But if you were measuring your mains electricity (wall voltage), it would mean it's time to call an electrician.

Atlant 14:11, 15 May 2007 (UTC)

Hmm. Just a warning that no one should attempt to measure their mians voltage without a proper safety voltmeter with fused leads and without proper training.

Energy from gravity

What would happen if you were far out in interstellar space tossing rocks trailing cable into the sun? Obviously the rock has (steadily increasing) velocity, so you should be able to capture mechanical energy from the cable and then let it "recharge" by allowing the sun to accelerate it again? A great distance from the sun the rock wouldn't accelerate much ("recharge" very rapidly) but eventually it would get close enough to produce considerable energy, right?

And of course, the obligatory black hole angle: what would happen if you were tossing rocks into a black hole? Would that be an infinite source of energy? It seems that if launching rocks into the sun would produce energy, it shouldn't be a problem if an event horizon is somewhere in between, as long as you don't expect to retrieve that rock..

I guess the question is: doesn't this violate the first law of thermodynamics? My guess is no, that you wouldn't be able to capture very much energy from the cable because fairly soon you're accelerated to the same speed as the rock. I suppose the more fundamental question is: where is this energy coming from that "enforces" the law of gravitation? Is it inherent in the mass? Does every combination of bodies in the observable universe have a potential energy to every other combination of bodies? And what about the uber-kilograms of mass that is revealed every second as the sphere of our observable universe expands at the speed of light? Shouldn't objects be wrenched out of orbit as black holes and quasars are "uncovered"? Or does our observable universe already have enough local mass to render insignificant any mass more than that distance away? --froth^t 04:26, 15 May 2007 (UTC)

How are you going to get usable energy out of this cable attached to the rock being pulled towards the sun? You'd have to be standing on something, otherwise the cable would pull you towards the sun too. Is that thing you're standing on also being pulled towards the sun? DMacks 04:35, 15 May 2007 (UTC)

Well presumably not as quickly as the rock, since the rock is much closer. But no you're not standing on anything, and that's why I suggested "you wouldn't be able to capture very much energy from the cable because fairly soon you're accelerated to the same speed as the rock". But obviously there is some energy to be had from the system of two bodies moving toward each other.. so where is that energy coming from? --froth^t 04:46, 15 May 2007 (UTC)

If you are on a planet then it's not a matter of simply throwing the rock, you have to launch it to escape your gravity first, which takes an enormous amount of energy, you will then probably spend the rest of the rock's trip to the sun recovering that energy. If the rock starts off in space, like a comet or something, then sure you could shoot a harpoon into it and then steal the energy from it, but since we have only just successfully landed the very 1st probe onto a comet, and the amount of energy and effort that required I doubt a rope with a generator on the end is going to recover even close to what was spent. Then the generator also would probably need to be shot back to earth somehow, using a lot more energy, or it would also just follow the rock into the sun. As to your question, yes I believe all mass has gravity as an inherent property and therefore there is potential energy between every mass in the universe, no matter how miniscule, it acts both ways, the earth exerts a gravitational force on the sun just as the sun does to the earth. Earth's effect on the sun isn't as noticeable, but Jupiter's effect on the sun is quite substantial, just as the moon's effect is very noticeable on earth. Vespine 06:03, 15 May 2007 (UTC)

One more thing for perspective, the point at which the gravity effect of the sun will outweigh the effect of the earth on your rock, only after which you can attempt to extract energy out of the rock without only getting back the energy you put in is called the L1 Lagrange point, about a million miles from earth. So your rope would need to be considerably longer then that, compare that to the circumference of earth is 25,000 miles, you can see another problem.. Vespine 06:12, 15 May 2007 (UTC)

Huh? You're not on a planet at all! --froth^t 06:39, 15 May 2007 (UTC)

All it does is shoot ya! 213.48.15.234 08:04, 15 May 2007 (UTC)

How about this for a contraption to get energy from gravity: Start with two asteroids which orbit one another at close range, tidally locked, in a highly elliptical orbit. Build a rigid connection between them with a sliding mechanism to adjust for the changing length between the two. This sliding mechanism will then be driven back and forth as they orbit one another. This motion can drive generators. Over time, this would change the orbit of the two asteroids, which would become more circular, I believe. StuRat 06:48, 15 May 2007 (UTC)

But wouold this produce more power than it took to make themechanism and find/get to the asteroids?

The Rance tidal power plant is a simply approach to the problem! Physchim62 (talk) 07:33, 15 May 2007 (UTC)

In any of these schemes, you are extracting mechanical energy from interactions between two or more bodies inside the gravitational potential field of the sun. This energy inevitably comes from a decrease in the total gravitational potential energy of those bodies - that is, their overall centre of mass must move closer to the sun as a result. The energy source is therefore not inexhaustible, although it's OK for a while. As Physchim points out, tidal power generators work on exactly this principle. Tidal power generation therefore leads inexorably to an increase in global warming!

Because of the inverse-distance law for gravitational potential, events in far-off galaxies fortunately don't affect us very much. --Prophys 08:57, 15 May 2007 (UTC)

AFAICT this is a question about how gravity works, but everyone seems to be sugesting ways to produce electicity from gravity :( The OP asks 'where is this energy coming from that "enforces" the law of gravitation? Is it inherent in the mass? Does every combination of bodies in the observable universe have a potential energy to every other combination of bodies?' :) Noone seems to have answered this, so I am asking it for them down here :] HS7 11:42, 15 May 2007 (UTC)

Asking how one gets energy "from" gravity is somewhat misguided. In a Newtonian universe, we can say that there is a gravitational potential throughout space, and that gravity is that variable energy (per mass); ${\vec {F}}:=-{\vec {\nabla }}U$, or "force" is simply the result of sitting on an energy gradient (you are accelerated down the gradient). Semi-classically, we can note that, just as a spring gains inertia from being compressed, so too does a mass gain inertia from being raised out of a gravity well (this is of course $E=mc^{2}$). Of course, we might then specify the rest mass of an object as its mass at infinite remove from all other masses; in practice, part of the rest mass of any real object is then "missing" because of its interaction with other mass.

So when you drop things toward a star (or whatever other convenient attractor), you are literally scavenging their mass energy for your own use (by letting the object represent some of its energy as kinetic energy, and then stealing that). If you drop them into a black hole, you do not recover infinite energy, but you can in theory recover their entire rest mass as they fall in (but note that this takes infinite time in any reference frame that does not fall in). This raises the interesting notion (although I cannot vouch for its literal correctness) that what mass is is one's gravitational potential energy as referenced against a handy Schwarzschild event horizon. In true general relativity, where gravity is not a force, this gets a bit more complicated: you are then taking advantage of a curved space to "circumvent" conservation of momentum: you have the object exert a force on you (and thus you a force on it) without accelerating it (although you are really accelerating the system of the star and the object). If one could in general get this "force without acceleration", simply tying a spring to a moving, unacceleratable object would allow you to get free energy forever.

As far as "new mass" in the universe, a simple explanation is that a (uniform, spherical) shell of mass exerts no gravitational influence whatsoever on objects within the shell. So the mass revealed by our expanding light cone, as long as it is at least approximately isotropic, has very little effect. --Tardis 15:47, 15 May 2007 (UTC)

Ah that last one's a good point, although I doubt it's anywhere near a constant increase in all directions since the speed of light is awfully slow and supermassive phenomena are so rare. Anyway, are you saying about black holes that since the rock has nowhere to go but down after passing the event horizon, you can capture as much energy from the cable as you want and the most that will happen is it will slow/stop until you let go again? Seems identical (though more efficient certainly) to using the gravity well of a star to do the same thing, although in that case you are able to recover the rock and it doesn't pull nearly as hard. But in either case, where's the energy coming from- is it only the rock's compromised potential energy within the system or does the very act of capturing the energy and accelerating along with the rock toward the star/singularity also contribute to the energy collected? --froth^t 18:05, 15 May 2007 (UTC)

1. About isotropy of the far universe: it has to be anisotropic in terms of the total distribution to have an effect; the individual blips are lost because of the inverse square law.

What about the Great Attractor? When that became causally connected to our universe, it must have caused quite a disturbance --froth^t 02:26, 16 May 2007 (UTC)

The Great Attractor's gravity at this distance is about $4\times 10^{-13}$ m/s², taking it to have $10^{4}$ Milky Way masses and the closest suggested distance of 150Mly. Next candidate? --Tardis 16:15, 16 May 2007 (UTC)

That number is impressively small, sure, but I've just realized a more fundamental answer: everything in the Milky Way experiences that tiny acceleration equally (remember that tides go as $r^{-3}$!), so it makes no difference in our local affairs. Moreover, we are always in free fall with respect to everything except the Earth, so a local experiment can't notice anything else's gravity anyway (and on this scale "local" is pretty big). --Tardis 16:23, 16 May 2007 (UTC)

1. About black holes: as I said, you can only get the mass energy of the rock. (For even a reasonably sized rock this is a lot, but it's not infinite.) All that happens is that, in your reference frame, the rock never stops falling (you never see it pass the event horizon, even), so you can keep running your pulley forever (but more and more weakly such that the total energy gained is, again, finite).
2. About the source of the energy: it's quite literally the potential energy the rock already had (and which already had inertia) before you started lowering it. In relativity "potential energy" is a particularly unfortunate choice of terminology because it is energy (and thus has inertia and gravity and such), not just some nebulous substance that might one day become real and start having an effect on the world. Gravity is simply a means of turning that kind of energy into the moving kind of energy — which still has inertia and gravity; this is "mass increase", although falling objects, until slowed down, are not changing in mass at all — and for distorting spacetime so that the falling object doesn't lose mass in its own frame. There really is no "source" for the energy; by dropping a stationary rock onto the surface of a planet, you are dropping a less massive rock than the corresponding rock that wasn't tied to a generator and landed hard, and you should not then be surprised that you have more energy on board your ship when you choose the former dropping strategy. The fact that the energy can be usefully extracted (we'd rather have a charged battery than an uncharged battery and a rock) is simply a result of the object's fall being reversible, which means that there is no entropy "bound up" with the energy released by the drop. --Tardis 23:04, 15 May 2007 (UTC)

Urgh - this is confusing. So you are in a spaceship - stationary relative to the sun and some large distance away. You have a large spool containing a few million miles of very thin cable - with the center of the spool attached to an electrical generator so you'll make electricity as the drum spools out cable. You tie the loose end of the cable to the rock - and toss it overboard. So to start with, the rock just floats slowly off into space at whatever speed you chucked it. But your spaceship is now falling towards the sun - you have to use your engines to stop it from falling. But now the rock is falling away from you...although it'll seem a lot like your engines are powering you away from it! However, your idea is that as the rock gets much closer to the sun than you are, the suns' gravitational field will increase and the rock will accellerate faster - eventually, producing more energy than your rocket is consuming to keep you hovering at the same distance from the sun. OK - that's probably a reasonable thought experiment. But what happens when the rock hits the sun (or melts or reaches the end of the cable or something)? At this point - you have no more energy income. All you can do is reel back the cable, tie another rock onto it and do it again. The trouble is that you don't have an infinite supply of rocks - because you have to use the power of your rocket engines to prevent both your ship and your supply of rocks from falling into the sun. So yes, you can extract energy from a falling body - but there is no free lunch here. It's no different from using a rope with a pulley and a rock on the end to generate energy here on earth. Your rocks have 'gravitational potential energy' by virtue of how far they are from the sun - when you drop them (attached to a cable), that turns into useful energy - but you've lost that gravitational potential energy - and the only way to get it back again is to haul the rock back up again - which takes more energy than you gained by dropping it. The fact that the gravitational field intensifies as you get closer to the source doesn't change that at all. If you change the experiment a bit and assume you are orbiting the sun instead of sitting still, you've saved the cost of keeping your engines running to stay in one place - but now the rock doesn't want to fall - it wants to stay in this nice zero g orbit. But if you pushed it out the door hard enough, and in the right direction (ie back along your orbit), the rock would start to fall into the sun and would unreel the cable - but you've still lost energy in the process because you don't have the gravitational potential energy of the rock anymore. If you are on a nice large planet instead of a spaceship - then you could certainly have an enormous supply of rocks - and powering your civilisation by launching large rocks into the sun with cables attached to them could theoretically work - but it's not "free" energy because the rocks you toss off of your planet don't come back. It might be a really cheap source of energy - and it might last you for a very long time - but it's not renewable - and it doesn't violate the laws of thermodynamics. SteveBaker 19:03, 15 May 2007 (UTC)

The worries about keeping your rock-dropping platform stationary are unneeded; just put your platform at some Lagrange point (between Earth and Sun, between Sol and Proxima Centauri, whereever) and you're set; then drop rocks a little ways away in equal amount in each direction and run two generators at once. The practical importance of this sort of technology would be taking rocks from reasonably high-potential areas (like the asteroid belt) and moving them (permanently) to a lower potential location like the Sun or a black hole; even the surface of Venus (where no one would mind the hail of rocks) would give you a specific energy of 54.7kJ/g, which is better than methane (not bad for "burning" a rock!). Obviously a black hole is the ultimate pit, and yields the full c² value of $8.9\times 10^{10}$kJ/g. No one's claiming that this is perpetual motion; indeed, I've tried to make it painfully clear that there is no "creation" of energy at all, even at some "expense" that would satisfy the first law. You're right, then, of course, that it's "non-renewable", but on the scale of civilization that we're talking about nothing is renewable, not even solar power! --Tardis 23:04, 15 May 2007 (UTC)

On a somewhat related note, I had a really weird dream last night. I dreamed that in the future, power was produced by "electrolysis towers". These towers were large columns with smaller pipes in the middle. Water would be produced by a hydrogen-oxygen fuel cells at the top of the columns, which would then flow down the pipe in the middle, generating hydroelectric power via generators as it traveled downward. The water was then electrolyzed into H2 and O2, which floated rapidly up to the top of the column due to the heavier gas (Think it might have been Xe or somthing in my dream, I forget. Lets call it UF6 just for kicks.) filling the columns. A high (90%) efficiency fuel cell (hey, come on now, its the future) converted the H2 and O2 into water, which then flowed down the column, starting the process over again.

Would this conceivably work, or would the columns have to be huge, 50 mi tall, and only make like 250W of power? Ninja! 23:44, 15 May 2007 (UTC)

No, I would expect the electrolysis of water to take more energy than you get back. StuRat 01:40, 16 May 2007 (UTC)

The solution is a Dyson sphere. - 2-16 12:31, 16 May 2007 (UTC)

StuRat, I realize that the electrolysis of water would use more energy (due to resistance and loss of energy to heat) than would be stored in the H₂, and that the fuel cell would also be somewhat inefficient, but, the idea is, that the energy of gravity uses hydroelectric power to create more energy than what is lost. Its really completely impractical, now that I think about it, but , as a thought experiment, you could either disprove the first law of thermodynamics, or.... prove that gravity is a continuous source of energy that is generated by the continuous loss of particle's mass to energy... O.o Ninja! 21:47, 16 May 2007 (UTC)

The failure of this device is that it takes energy to force the heavy gas aside at the bottom of the column (PdV and all that). That energy is what you're attempting to tap by having the falling water run a turbine. --Tardis 23:15, 16 May 2007 (UTC)

Antidepressants

What do they do to the mind? Chemical effects to the brain are I assume widely understood, but can anyone who's taken them tell me what they actually do to you? Does it just improve the disposition of the person or what? I certainly understand feeling good and readily laughing, etc, and also being depressed and inexplicably moody.. but do the drugs actually do anything besides affecting that aspect? Seems hard to believe that a person's reactions and general smileyness could be affected by something as insignificant as disposition instead of deeper-seated things like personal philosophy --froth^t 04:44, 15 May 2007 (UTC)

It varies. When I took Paxil (1994), my mother and my ex-wife both commented that I was more willing to approach people; that's the most striking effect I remember. Later I took Prozac and Wellbutrin, with mixed results; at best, they simply relieved me of the occasional attacks of despair. When I stopped taking Wellbutrin (because of palpitations) my mood actually improved for a few weeks. —Tamfang 05:18, 15 May 2007 (UTC)

Basically, they raise the level of serotonin and other neurotransmitters in the brain. I tend to think of hereditary depression as the diabetes of the mind. It hits a lot of males at 40 and gets progressively worse. People tend to self-medicate with alcohol and drugs. The anti-depressants are a better alternative than addiction and suicide, but they do tend to level things out, and reduce creative spurts. --Zeizmic 11:30, 15 May 2007 (UTC)

I think the most common kind now is SSRI's (Selective seritonin reuptake inhibitors), which reduce the rate at which Seritonin is removed from the brain, thereby increasing overall levels. I had a kind of messed up childhood up until about age 12, and was on SSRI's for about 2 years (age 10-12)- I assure you, not by choice. I never really understood this, as I never really felt depressed in the first place, I think it was mostly to due my percieved "behavioral disorder" which now seems to be more of a PG/ADHD-BD misdiagnosis (Huh, no article about that, think I might write one). But anyway, more to the point, most of my friends told me that it did improve my mood and disposition somewhat, at the expense of a loss of personality and creativity, it kind of mellowed me out. Oddly enough, I actually felt better for a time after I stopped taking the medicine, though perhaps I am a bad example as my doctor (but unfortunately still not my mother and the morons on my district's school board, but thats not the point) both agree that I was misdiagnosed. Hope I spent more time helping than I did whining about grades 5-7 :/ Ninja! 23:57, 15 May 2007 (UTC)

Oh, on another note, I think some of the newer antidepressants also work by affecting noropinepherine (oh boy, I misspelled that, I'm certain...) Ninja! 00:06, 16 May 2007 (UTC)

It's norepinephrine, also called noradrenaline. Icek 12:35, 16 May 2007 (UTC)

When I was younger, I was diagnosed with ADHD and Bipolar disorder, because it was the late 90s, and it was cool to be a kid on ritalin. I was given Ritalin and Depakote. I don't remember exactly what it was for, but I'm fairly sure that the Ritalin was to calm me down, and the Depakote to cheer me up, although oddly enough, my mother had taken depakote a couple decades earlier for her seizures. Anyway, I don't remember it very clearly, but I do remember that while I was on them (both of them), it actually made me more violent and angry. I "forgot" to take my pills one week, and was much more well behaved, and in general, normal. I know that once I quit taking them, I improved quite a bit. One side effect I definitely remember was weight gain, due to an incredibly unprofessional shrink. Still haven't fully gotten over that. I don't know if there's any medical proof behind it, but I firmly believe that one of the three drugs (Ritalin, Depakote, and Neurontin), or a combination of them, messed my memory up extremely badly, as I have very little memory of even huge things from then, and my memory still suffers some, mainly short term, although it's improving. I'll have memories I should have missing, like I can remember a name, but even when I'm given very detailed descriptions of people and how they act, I can't remember 'who' they are, or I can remember 'who' someone is, but their name is completely lost on me, and I'm not talking about random people here. Hell, up to a couple years ago, I had trouble remembering faces of even close family and friends, I still have times when I can't even remember what my own mother looks like. Obviously chemicals can have a very real effect on how people act or feel, look at narcotics, booze, any number of things. I still recommend against them though, if I had to go through it again, knowing what I know now, I'd much rather go to therapy three times a week than put that stuff back in my blood stream -- Phoeba Wright^OBJECTION! 02:35, 17 May 2007 (UTC)

electron and proton attract each other then why there are distance between them in an atom ?

consider a hydrogen atom which is simply made of a n electron and a proton ; but there are distance between these two . why these electron and proton do not simply touch each other to form an atom ? —The preceding unsigned comment was added by 202.56.7.134 (talk) 09:09, 15 May 2007 (UTC).

1. They're an atom without touching each other. Electrons and protons don't touch, and we still have atoms. Plenty of them in fact. Did you mean nucleus?

2. "Touch each other" doesnt really happen at atomic scales. The electromagnetic fields interact.

3. The Earth and the Sun are in a nearly identical situation, they are attracted by gravity. Why don't they touch each other to form the death of humanity^TM?

Have you studied Centripetal force?

(I know i'm using a Bohr model here, anyone care to explain it with QM?). Capuchin 09:16, 15 May 2007 (UTC)

Yeah it's certainly not centripetal force! The electron doesn't sit in one place in space, it really lives in a sort of probability cloud all around the atom. It's hard to picture, but effectively the electron can be found anywhere within this area around the nucleus, including 'touching' the proton, but is simply more likely to be found a slight distance from the nucleus. It's all a bit quantum. I am sure the article on hydrogen atom would help. 137.138.46.155 11:33, 15 May 2007 (UTC)

Also atomic orbital. DMacks 14:50, 15 May 2007 (UTC)

Unfortunately, none of the above seems to really answer the root question (which I'm reading as "protons are positive, and electrons are negative. Since opposites attract, why don't they smash together?" -- correct me if I'm wrong). It's an excellent question, and unfortunately doesn't have a simple answer. The best I've come up with is to reference quantum electrodynamics, which notes that at very small (i.e. atomic) scales, electromagnetic forces aren't really doing what we think they're doing at macro scales. That is, at their smallest most fundamental level, opposites don't attract. Rather, they swap mediating particles (in this case, virtual photons) that affect the nature of the originally exchanging particles.

So, as best I read all this, a proton and an electron aren't really attracted to each other. Rather, they bounce these virtual photons back and forth, which leads to the behavior described in the above referenced articles like atomic orbitals. By the time you get up to large scales, the sum total of the behavior is such that opposite charges, for all intents and purposes, do attract. It's weird, yes. And I don't know why virtual photons make electrons do the things they do. However, that appears to be the core of the answer. — Lomn 15:49, 15 May 2007 (UTC)

Two interesting issues come to mind here:

Sometimes something approximating the macroscale concept of "an electron colliding with a proton and sticking" does occur (electron capture decay).

One fundamental thing that's really hard to understand at all, let alone remember and see all the resulting effects, is that electrons are not really point particles. They can do all sorts of things that a macroscale object cannot, and they don't have definite positions and motion around the nucleus.

Even in atoms, the idea of electrostatic attraction is a good model for lots of behaviors (for example, decreasing atomic radius going across each row on the periodic table), but it's not the complete picture.DMacks 17:23, 15 May 2007 (UTC)

Electrons "orbit" like planets around the nucleus (protons + neutrons) of the atom. These electrons must orbit at a certain speed. If they went any faster, they'd escape into space (or move into a wider orbit). Any slower and they'd crash into the nucleus (or move into a smaller orbit). So faster electrons orbit farther from the nucleus.

To change speeds - and so change their height - they'd need to change their energy. This is not possible (due to conservation of energy) unless some additional force comes into the system. For example, a photon with enough energy can knock an electron completely out of orbit (this is ionization).

This explanation mirrors the Bohr Model, and is false but a good approximation. A better model uses quantum mechanics and modifies the picture in 2 ways. (1) The atoms no longer orbit, but are sort of fuzzily spread out (delocalized) along the entire path of the orbit, so the electron as a single point becomes an fuzzy circle or sphere. (2) It allows only certain heights (and paths) above the nucleus to be valid orbits (see atomic orbitals).

Electrons will try to get into the innermost orbit (remember, QM says only certain orbits are allowed). Electrons can move into smaller orbits if there's not an electron in that orbit already (Pauli's exclusion principle). To move into a smaller orbit, they need to have less energy, so they convert the excess energy into a photon and emit it.

To answer why the electron doesn't lose all it's energy and crash into the nucleus, I guess it falls out of QM, but don't ask me how. I guess that if it did happen, it would interact with one of the protons, and make a neutron (β+ decay). But this would require extra energy, so would not be possible.

This is really a brief overview, and a hand-wavey description, with many generalizations and omissions. Bohr Model is a good place to read more; the Standard Model is the currently accepted model. --h2g2bob (talk) 17:25, 15 May 2007 (UTC)

There are many answers to that question. Oni is that, on an atomic scale, electrons don't act like little balls or points but wavelike and thus don't have a pointlike coordinate position but an expectation desnsity.

A quite different answer is that if they fell into the nucleus and reacted with a proton to form a neutron, that would require additional energy, as a neutron is slightly heavier than the mass of a proton plus the mass of an electron. 84.160.233.3 19:12, 15 May 2007 (UTC)

of course all this could just be pseudoscience, and there might actually be a totally different reason that we haven't discovered yet.

final starch question

forget all my previous questions about starch (to which I didn't get answers). I just need to know a quantitative test for stach. Something I can do to something with starch in to see how much there is. Say I have a leaf grown in darkness somewhere and I want to see how quickly stach in it is replaced, I would need to do something to the leaf occasionally to see how much starch had been produced. How would I do this? Or you could refer me to another websight which can tell me if you prefer. —The preceding unsigned comment was added by 172.142.244.7 (talk) 11:33, 15 May 2007 (UTC).

Seeing you display such a stack of insite, I'd like to help. "quantitative test for starch" in a Mountain View search engine returns 979 000 answers. Some just use spectrometers and amylase. So this is my question : what kinda devices and products may you use easily in your job (or homework) ? -- DLL ^{.. T} 18:49, 15 May 2007 (UTC)

Not spectrometers. I am quite sure of that. I was hopeing there were chemicals that can change colour, or something. I have already tried searching the web, and didn't find anything apart from a few pages vaguely similar to my question. I am apparently not very good at getting computer stuff to work.

Well, the classic Iodine-KI reagent test will reveal the presence of starch - but not the quantity. I suppose you could somehow use a very dilute version of the starch and match the resulting colour to some kind of a colour chart. You could calibrate the chart with known quantities of starch in increasingly dilute amounts. It wouldn't be really exact - but maybe good enough for your test. SteveBaker 17:08, 16 May 2007 (UTC)

Hospitals

How many hospitals are there in the United States?170.232.128.10 14:31, 15 May 2007 (UTC)

As of 2005, 7,569. Hipocrite - «Talk» 14:42, 15 May 2007 (UTC)

That impresses me as a small number. --BenBurch 14:52, 15 May 2007 (UTC)

Average of 150 per state is small? I guess it's all about lies, damn lies, statistics, and one's frame of reference:) DMacks 15:00, 15 May 2007 (UTC)

According to the OECD, in 2003 the US had 2.8 acute care hospital beds per capita thousand, vs 4.1 for all OECD countries.[2] Thus, we are below the developed country average in beds-per-capita. Hipocrite - «Talk» 15:06, 15 May 2007 (UTC)

Hope you don't mind me editing your remark, but 3 beds per person would be a trifle excessive, I feel. Given the US spends $5,635 per capita per year on healthcare, more than twice the OECD average, I hope they're very comfy beds. Algebraist 15:26, 15 May 2007 (UTC)

A quick note: that's 2.8 beds per 1000, not per capita. Otherwise you'll be left wondering why anyone would care if a patient has a fourth bed or not (or why it matters). There's also the question of how the metrics should be applied. For example, this MSNBC article notes that the US is generally good with regard to timely access to major surgery and preventative care. Perhaps that affects the need for hospital beds per capita (or maybe it doesn't, or maybe it puts the US further in the hole). Point is, statistics in isolation can provide a dangerously unwarranted level of confidence. — Lomn 15:30, 15 May 2007 (UTC)

Thank you both for the correction - yes, it is, obviously, beds per thou. Hipocrite - «Talk» 15:38, 15 May 2007 (UTC)

Absolute Uncertainty of a mean

If you have a set of data, knowing the absolute error of each object in that data (e.g. 20±1cm), and then find the mean of that data, what is the absolute error of the mean, assuming all of the elements of the data had the same absolute error?

e.g.

18±1 17±1 15±1 14±1

The question is phrased as find the mean (obviously 16) and then the absolute uncertainty of this mean.

The mark scheme from the paper I am looking at is talking about finding 1/2 or 1/5 of the range, or 1/2 or 1/5 of the range ignoring the highest and lowest answers.

Can you please explain the methods for finding these means? Or point me in the direction of where to look?

Many thanks!

--Fadders 15:30, 15 May 2007 (UTC)

See propagation of uncertainty, although you should be careful about whether you are claiming by $z=x\pm y$ that "z is certainly on $[x-y,x+y]$, but may be anywhere in that interval" or that "z is probably at a remove from x no greater than y, but will often be significantly closer or somewhat farther away" or any other such formulation. (In the second case it is commonly assumed that z is normally distributed.) The values you are reporting are really probability distributions (in some interpretations), so you need to give them a shape (presumably described by your "error" value) before combining them.

In the likely-correct interpretation as a normal distribution with a standard deviation as the error, you should look at that page and at, say, the variance of a sum to find a rule for the mean of your data. --Tardis 16:07, 15 May 2007 (UTC)

Hmm I'm not sure that's what I'm after.

The question is at http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PHB3-W-QP-JAN05.PDF (page 3)

The mark scheme has the answer at http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PHB3-W-QP-JAN05.PDF (page 4)

Thanks! --86.156.40.31 18

40, 15 May 2007 (UTC)

hydroponics

I recently read that some grow hydrponics by filling a ditch (in the ground) with water, and then having some sort of pipe with water which is connected to the water in the ditch- in this "pipe" grow hydroponics.

What is the purpose of this way?

do the hydroponics draw any nutrition from the soil by way of the water?

Thanks for your help

Tirzah Segal

email removed to protect you from spammers —The preceding unsigned comment was added by 86.135.202.234 (talk) 16:31, 15 May 2007 (UTC).

Chemistry (In general)

Is the only way to understand Chemistry (other than constantly solving extremely complex mathematics via approximations) just knowing how each chemical element reacts ? Sure, for the first two rows of the periodic table, most of the elements are well behaved with respect to the duet-octet rule and many bonds can be understood with solely this rule. Of course some subtleties arise with considerations of electronegativity and ionization energies, but it doesn't really get too unpredictable (even though some molecules seem to be quite different (Al₂Cl₆)). But then it seems on the lower rows, no real predictions are made, just observations. Why is it so often Mg²⁺ ? Why can Mn be reducted to +7 and not Fe to +8 ? Why is Hg liquid at normal temperatures ? Even the predictions based on comparing between rows aren't always very true, and other oddities like Zn reacting to HCl and not Cu. Surely there are precise explanations of how one can expect species to react ? I understand most imaginable (but not absurd) molecules can exist, and then one has to evaluate how stable they are. But still, what are the best rules that suit all ? I just get confused with the different treatments for different elements (Transition metals, semi metals, non metals, etc...), even though it is understandable differences must exist. As it is now, I'm totally unable to say if such or such molecule is stable (a book I'm reading always comes up with new explanations each time of why such molecule is stable : one time it's with atomic orbitals and combinations, one time with hybridization, one time with redox principles, ...). Are all the elements so different that one has to differentiate them clearly to be able to study their behaviour ? And even so, how does it work, what makes it possible to not study individually all elements in most cases ? --Xedi 18:43, 15 May 2007 (UTC)

Chemical properties of hydrogen compounds can have vast differences depending on the state of matter (solid, liquid or gas). The difference in chemical properties is related to:

a. the dissociation of H+ from the hydrogen compound into solution.

b. the dissociation of OH- from the hydrogen compound into solution.

c. the energy threshold required to break the covalent bonds in the solid.

d. the slight cohesion of the liquid solvent forming the aqueous solution.

—The preceding unsigned comment was added by 72.64.128.23 (talk) 18:46, 15 May 2007 (UTC).

Well, yes, but that stays a quite basic description. I do understand how Brönsted acids/bases work in water, but that's just one infinitesimal part of chemistry. I quite like how the K_A/pK_A system works, as one can just write down a reaction and see how it evolves, just knowing the K_A/pK_A of some species. But this still depends on "knowing" how the molecules react (ie knowing their K_A/pK_A). For more general reactions, there isn't even this, and it seems difficult to predict how atoms will combine, without just knowing how they react from observation. --Xedi 19:22, 15 May 2007 (UTC)

"Physics is the study of how things behave similarly. Chemistry is the study of how things behave differently" - George Pimentel. Delmlsfan 19:43, 15 May 2007 (UTC)

Haha, well, quite true. Sadly physics are too complicated (mathematically) here. Oh well. --Xedi 19:47, 15 May 2007 (UTC)

Well, a couple things on this one.

• Mg is reduced to a 2+ ion because that allows it to have an ideal electron configuration, eg., eight electrons in its valence shell (2S and 6P)
• Mn and Fe don't reduce to +7 and +8; this is not ideal for them. Transition metals often prefer to either shed all of their D orbital electrons or about half of them, as these are both fairly stable; still other transition metals prefer to do only 2+. Except for Ag+; and I beleive Hg has a 1+ state as well, though I think its diatomic or something weird like that, I forget about that stuff, I do organic. Anyway, back to the point:

Mn does have a +7 oxidation state. And you're right that the Hg +1 state is diatomic; it's Hg₂²⁺. See Mercury(I) chloride as one example. Chuck 23:28, 15 May 2007 (UTC)

I suppose I hadn't thought of MnO₄^-. I was thinking more of just an Mn⁺⁷ ion floating around in solution, which of course wouldn't happen. Ninja! 21:28, 16 May 2007 (UTC)

• As far as Zn reacting with HCl, Zn is more reactive than Cu. There should be an explanation for this at Reactivity series (if there isn't let me know, I'd need to edit that article some)
• As far as what molucules can exist and what can't- this is a very broad area. I'd check out the article on Lewis structure for this one; they can be helpful for predicting if a certain species exists.
• I think I forgot to mention Hg being a liquid. This is due to Intermolecular forces, especially Metallic bonding. I would check out the article on Mercury for this one.

I think that answers most parts of your question. If you have questions about a specific element, I'm sure the article about that element would be quite helpful; if you have some question about something more specific feel free to drop me a message on my talk page; I'd be happy to help. Ninja! 23:06, 15 May 2007 (UTC)

Hi,

Sorry about the Mg²⁺ one, yes that one is quite simple. I actually meant Mn²⁺. So why do so many transition metals reduce to 2+ ?

That [Reactivity series]] is very interesting and shows well the differences in reactivity. But still, why would Zn be so much more reactive than Cu ? I mean, Cu and Zn are nearly the same, only that has both s and d full (and Cu's electron configuration also doesn't fit in with the general trend of filling s first : [Ar]4s¹3d¹⁰ (same for Cr I suppose) : this conforms to your explanation of prefering to half-fill or entirely fill the d orbital, same goes for Ag and Au underneath Cu that also don't react much). This seems to be another example of how chemistry works : we get tables of what reacts in general with what, as in that reactivity series or with redox potentials. But for some elements it seems really strange to me. I feel quite confident I could come up with many more questions and that finally it would be as if there was an explanation for nearly every element (Tc being unstable, B being strange, ...).

Thanks for the explanations still. Just that so many things seem strange to me.

http://img518.imageshack.us/img518/1899/ptinorganicxf4.gif

-Xedi 11:42, 16 May 2007 (UTC)

Dark matter

Most mass in the univers is in the form of dark matter, how is it that we don't see even the gravitational effects? With huge additional quantities of mass around, planetary orbits should be different, stars should collaps at a different rate, and, finally, black holes should grow at a different rate. (Even the 'darkest' matter should not be able to escape again.) 84.160.233.3 19:18, 15 May 2007 (UTC)

We do see the gravitational effects - that's how we know that what we can see doesn't tally with the mass that is measured to be there. →Ollie (talk • contribs) 19:25, 15 May 2007 (UTC)

As far as I know we see only effects about gravitational lensing. There should be other, more direct effects. 84.160.233.3 19:50, 15 May 2007 (UTC)

We see that the orbits of stars around their galaxies are not as either Newtonian mechanics or general relativity (quite similar predictions at those scales) would have us believe. The only possible explanations to this is that we are very very wrong about how much stars weigh, our theories of gravity break down at huge distances, or there is mass that we can't see (it is "dark"). Most astronomers agree (I actually don't know of any who don't, I'm sure dark matter is a good read for this) that the third possibility is the correct one. Someguy1221 19:57, 15 May 2007 (UTC)

We see no effects on planetary orbits in the solar system. The dark matter is probably just elswhere in the galaxy or spread very evenly around. However, see Pioneer anomaly for another possible gravitational effect of dark matter. —The preceding unsigned comment was added by 84.187.9.82 (talk) 20:16, 15 May 2007 (UTC).

Now that I look at it, Dark matter is a very good read on this issue. And dark matter is everywhere, dude. Someguy1221 22:29, 15 May 2007 (UTC)

Yea, it's a good read and the article can't be blamed if science can't do better as of now. Anyway, if dark matter isn't very hot (fast), it should gravitationally agregate insides big stars and significally influence the point of gravitational collapse. Even if it were extremely fast, it would be cought by black holes from where it is no escape. Black holes would grow much faster then. This effect should be detectable. Why isn't it? 84.160.233.3 00:59, 16 May 2007 (UTC)

How do you know this effect should be detectable, have you calculated the effect? We can barely detect black holes as it is (because they are black!) and rely on seeing their gravitational effects, we certainly haven't been observing them over a long enough time scale to see how they grow. Why Dark matter is spread evenly rather than following the patterns normal matter has collapsed into is unknown. But then we do not know really what makes Dark matter up at all, only that it's gravitational effects are detectable. There are three main ways we see this, Gravitational lensing, rotation curves (i.e. speed of rotation of matter in galaxies and galactic clusters) and through projects like WMAP which fit all the observables we have to the development of the universe as a whole. From this they deduce how much ordinary matter, dark matter, dark energy etc must be in the universe to make it how it is today. I guess the answer to the question is that dark matter tends to have large scale rather than small scale effects. And we'll get back to you when we know what it is, the LHC particle accelerator switching on 2008 could very likely see some particles which are dark matter candidates, so watch this space. Cyta 11:56, 16 May 2007 (UTC)

The answer is obvious. All ninjas are made entirely of dark matter. Since the dark matter is contained within ninjas, we can never detect it. Because ninjas are awesome. - 2-16 12:34, 16 May 2007 (UTC)

Lead-acid batteries

Do lead-acid batteries of the type used in UPS systems, power wheelchairs, etc ship charged or discharged? Also, is it normal for a lead-acid battery to make a fizzing sound when charging? 65.188.253.13 19:23, 15 May 2007 (UTC)

Read Lead-acid battery. I learned a lot reading it. They are always kept charged, and that's why my friend had a bum battery when he bought a show car; they have to charge every 2 weeks. Back to your problem: if it fizzes and inflates like a balloon, that's not a good thing! Since this answer is a bit late, let us know if you survived the explosion. --Zeizmic 21:50, 15 May 2007 (UTC)

A lead-acid battery only fizzes when it's fully charged and breaking down water via electrolysis. It's not a normal condition but if you have a long string of batteries in series, it might happen when you're first charging the string and the batteries are "equalizing"; that is, they may have initially been charged to different points and the batteries that reach full charge first begin to "boil". Assuming these batteries use ordinary unsealed cells, then after that first charge, just top off all of the cells in all of the batteries with distilled water. But if they keep fizzing after that first full charge, then something may be wrong.

Atlant 22:58, 15 May 2007 (UTC)

Sealed or valve-regulated lead-acid batteries used in many DC power applications are stored and shipped fully charged, and can hold a reasonable charge for over 3 months. Past 6 months, and breakdown can happen as the battery flat-lines and starts to chemically deteriorate. If your battery is fizzing and it's a sealed or valve-regulated (meaning nonspillable) then it is deteriorating and I would not trust it to work for very long. These types are not fillable so as they burn off water there is no way to put it back! --Jmeden2000 18:25, 16 May 2007 (UTC)

Exercising and Sweaters

Does wearing a sweater help get rid of fat or calories during exercise? Or does it just get rid of water weight? PitchBlack 19:40, 15 May 2007 (UTC)

Exercise that requires more energy uses more calories, because the calorie is a measure of energy. So what you are really asking is, "Does wearing a sweater during exercise make you work harder?" And the answer is: yes, but not much. Wearing a sweater requires you to work harder, since a sweater has weight; you must carry it around with you as you exercise, and that takes some additional work. But not much, since a typical sweater is not very heavy. And the same effect could be achieved by holding the sweater in your hand as you exercise. --Tugbug 22:18, 15 May 2007 (UTC)

It would make you sweat more, which requires slightly more work I suppose, but you're likely to become tired more quickly than just exercising without a sweater, which is obviously preferrable. --froth^t 22:27, 15 May 2007 (UTC)

Well, it's not going to "burn" or "melt" any fat off. The best way to lose weight through exercise is to actually exercise and not give up on it, which will be considerably easier if it's somewhat pleasant to do, which will be considerably more likely if you're not doing it in a sweater. --TotoBaggins 17:52, 18 May 2007 (UTC)

How many HP do humans have?

So, how many?217.95.9.251 20:27, 15 May 2007 (UTC)

Over nine thousand. --Xedi 20:31, 15 May 2007 (UTC)

There's an answer, surprisingly enough, on the horsepower page. DMacks 20:34, 15 May 2007 (UTC)

Geez DMacks, you could have made it easier. I finally found it: "a healthy human can produce about 1.2 hp briefly...and sustain about 0.1 hp indefinitely, and trained athletes can manage up to about 0.3 horsepower for a period of several hours." Clarityfiend 20:40, 15 May 2007 (UTC)

How many 'homepages' do humans have? What, each? Or collectively? --Manga 20:47, 15 May 2007 (UTC)

It changes with each level depending on your constitution. --Russoc4 20:58, 15 May 2007 (UTC)

Defense is more important anyway --froth^t 22:25, 15 May 2007 (UTC)

I thought Hit points when I first read this, haha. :) Vespine 22:30, 15 May 2007 (UTC)

Umm...doesn't it mean hit points? bibliomaniac15 00:19, 16 May 2007 (UTC)

I thought it was talking about Hewlett-Packard, although the article doesn't give an idea of the total number of HP products owned by people around the world. Then again, it could be anything on HP (disambiguation), in which case I would point out that humans have one hippocampus each. Confusing Manifestation 00:46, 16 May 2007 (UTC)

Whatever they are, they taste very good when liberally coated with HP Sauce. (That's small l liberal, btw; not wanting to offend any British parliamentarians out there.) -- JackofOz 00:53, 16 May 2007 (UTC)

You just need to balance your food recommendations to insult all POVs equally, might I suggest a nice chicken catch-a-Tory ? StuRat 01:22, 16 May 2007 (UTC)

Well, a human's HP depends on their STR and CON values, of course. And their level.

If we seriously consider the question of how many hit points a person has, we need to acknowledge that it's a flawed question in the first place. Different gaming systems have different amounts of hit points. In Fire Emblem, 60 is the absolute maximum, whereas in Pokemon, 60 hit points is incredibly weak, with the maximum being well over 300. The only way in which we can derive a "universal hit point scale" is to find the average endurance of a human being and convert it to a numerical value. Of course, many factors need to be considered in this ("endurance" is rather vague); Body fat? Stamina of running? Bench press? Even if we can find the average human's endurance, what scale will that be on? Will an average human have 100 hit points, where 50 HP would be one half, or will an average human have 10 hit points, where 5 HP would be half? Reexamine the question, methinks. - 2-16 12:39, 16 May 2007 (UTC)

resistance of copper to strong alkali

To cool or heat a 10L tank of liquid quickly I am considering immersing a coil of copper tubing in the liquid and running hot or cold water through it. The problem is, the liquid in the tank is pH 12 (fairly alkaline); I am wondering if the alkaline will cause a lot of copper to go into solution. I am not actually worried about mechanical failure of the tubing, I just would prefer not to add a bunch of copper to my solution.

Any ideas on how to find out effect of alkali on copper? Alternatively, can you suggest a coating for the tubing that wouldn't be too bad of an insulator? Or do you have other ideas for a small scale heat exchanger? ike9898 20:52, 15 May 2007 (UTC)

I'm Not sure about the reactivity of copper with a base, but alternatives would be: cool or heat the tank directly, use a metal less reactive than copper, or find out what the inside of the tank is made of and use that material. --Russoc4 21:01, 15 May 2007 (UTC)

The tank is glass. I have considered getting a pyrex coil made, but it wouldn't be as cheap and easy as the copper. I'm also interested in other methods for benchtop heat exchanging. I can spend a little money if I need to, say $1000. ike9898 21:06, 15 May 2007 (UTC)

I don't believe any significant reaction will occur between Cu and OH- (That is, alkali conditions). Cu(OH)2 (Copper Hydroxide) Isn't formed spontaneously by reaction of Cu with a base that I know of, as you have to put energy in via, for example, electrolysis. I'm fairly certain that the copper will hold up fine in this environment. Ninja! 23:29, 15 May 2007 (UTC)

Dark patch on hand

On my right hand, where my thumb is connected to the hand, there is a patch of skin quite a bit darker than the surrounding area. When I put my thumb against my hand, this dark area ison the right hand side of the "crease", and is about 2 pencil-top erasers wide. It goes up along the side for about 4-5 pencil widths. I am a white male, 15 years old, and have had adbominal problems in the past few months, and have had moles throughout my life (some removed). Is this something I should worry about? 22:46, 15 May 2007 (UTC)

According to the top of this page, "Do not request medical or legal advice. Ask a doctor or lawyer instead." Although you might get some good information about this from Wikipedia, if you're concerned it would be best to see a doctor instead. Ninja! 23:31, 15 May 2007 (UTC)

Agreed, see a doctor. Some moles can become cancer, so it is important to have a dermatologist check them regularly, especially if they change in size, color, or texture; or if they become painful or itchy. Moles with an irregular boundary are more likely to become cancer, so especially see a doc if you have those. StuRat 01:11, 16 May 2007 (UTC)

Definitely see a doctor, who might mention the ABCD guideline. --TotoBaggins 18:06, 18 May 2007 (UTC)

biology

what are the common characteristics between animals and all living things? —The preceding unsigned comment was added by 144.120.8.37 (talk) 23:50, 15 May 2007 (UTC).

They all like to avoid doing their own homework ? StuRat 23:32, 16 May 2007 (UTC)

Try a google search, there is a lot out there. David D. (Talk) 03:53, 16 May 2007 (UTC)

DNA - although viruses don't have it - it's debatable whether we should call them "living things". Cell structures are present in everything other than viruses - so probably there are a range of structures within the cell that are common to most life-forms. If you are talking about things other than physical structures, we have: Reproduction, Nutrition, Growth, Excretion, Respiration. SteveBaker 11:39, 16 May 2007 (UTC)

The ten unifying themes of life (if I recall correctly) are evolution, homeostasis, reproduction, movement, adaptation, reproduction, and a few others which I can't be arsed to dig up right now. - 2-16 12:41, 16 May 2007 (UTC)

The fundamental (basic) unit of life is the biological cell; although even some viruses (such as papillomavirus, which causes warts) have DNA, they are not cellular and require a host cell to replicate, so are not regarded as "alive". Bendž

|Ť 13:39, 16 May 2007 (UTC)

life. and death. but not taxes.

mouse

I have a mouse that has been living in my gorage that i want to catch for a pet ive been seting traps but its goten away with the food from all the traps with out seting them off. So far the only times that the mouse has goten the food from the traps was dering the day when im at school and at night when im sleeping. Is there a way i can find out if it is just taking care of babeys without takeing every thing out of my gorage. Because i dont want to trap it if it is taking care of young. thanks --Sivad4991 23:55, 15 May 2007 (UTC)

Catching a wild animal for a pet is often a bad idea. For one thing the animal is likely to be infested with a variety of parasites. You are better off getting a pet mouse from a pet store. The mouse itself will be quite inexpensive compared to the cost of the cage etc. that you will need for it. 169.230.94.28 00:04, 16 May 2007 (UTC)

I'm assuming you want to get the mouse out of your garage, but want to be humane about it, and keeping it for a pet was your idea of how to do that. Another suggestion is to catch it humanely, take it out into the woods, and release it, then get a disease-free mouse from a pet store to keep as a pet, if you want, as suggested above. There are special traps designed to trap mice but not harm them. As for the mouse having babies, you don't even know if it's female, so I think it's unlikely it has babies. Also, you probably have many mice, not just one. StuRat 01:04, 16 May 2007 (UTC)

Don't trap the mouse. Wild animals do not like to be contained. I have a garden with many fruits and vegetables, and squirrels have taken note of it. Now, I don't mind sharing the fruits of my labor (no pun intended) with a fellow animal, but the darned things just take a bite and leave the rest to rot! After a few months, I got tired and decided to get a squirrel trapper. I tried my best to find the most "benevolent" one. But the problem here isn't the trapper, it is the animal itself. When I caught a squirrel, the poor thing started abrading itself by banging its nose against the cage. Animals aren't that different from us. How would you like it if you were put in a cage, or kept as a pet? After that incident, I did not harm the squirrels again. But now I share with them. I specifically leave a few fruits out for them in a special corner in which they seem to enjoy sitting. And as another bonus, they chase away the small birds that peck at every single fruit (they don't even eat them, apparently looking for worms inside). As for your mouse, unless it is causing property damage, like chewing through wires, then it would be best to leave it alone. I have seen a few mice rummaging around in my garage myself! But there was one thing I noticed; ever since the mice moved in, I haven't seen any bugs in my garage, except for the occasional spider. But spiders are a different topic. I used to enjoy killing spiders, until one day I was bit by a mosquito. I chased that thing all over the house, and it flew into my bathroom and I couldn't find it. The next day, I looked in the corner of the cabinet under the sink, and there was a fat mosquito stuck in a spiderweb =). Moral of the story: Weigh the benefits of having so-called "pests" around.--Kirby♥time 03:19, 16 May 2007 (UTC)

If the mouse is suckling young, its nipples will be more pronounced. Of course getting close enough to see this would be a challenge in a wild mouse. It will only suckle its pups for about 3 weeks, though, at which point they can fend for themselves. Even if you trap the mouse, the pups will likely survive for a significant time (perhaps about 5 hours if they are young, a day or so if they are a little older) without suckling, so you could always release her again and she could go back to feed her young. Do be careful though, as wild mice do harbor disease and they can give a nasty bite. Rockpocket 05:15, 16 May 2007 (UTC)

Wild mice continuously have babies. You can't dig them out of the compost, or trap them without disturbing a nest. Think of hantavirus when you want to let them live a happy life in your house. --Zeizmic 12:28, 16 May 2007 (UTC)

If you are considering letting it (and its possible friends) live happily in your house, consider that a mouse can give birth to litters of 6-8 pups after 3 weeks of gestation, and can get pregnant again within 24 hours of birth, and that those pups themselves become sexually mature after 6 weeks [3]. Do the math: two happy mice very rapidly become an astonishing number of mice. --mglg_(talk) 16:18, 16 May 2007 (UTC)

Years ago I discovered that a mouse had gnawed its way into a plastic bag of birdseed in the basement. I don't mind setting a trap that kills a mouse instantly. I do not like seeing a mouse with a trap snapped on its hind legs, trying desperately to drag its crippled body away. I object fundamentally to gluetraps, which are right up there with crucifixion. Poison leaves a dead animal somewhere out of sight stinking up the place. I decided to just catch and transport the villain. I built Trap 1.0 by putting away the bag of birdseed where he could not get at it, then leaving a trail of birdseed along an inclined plank which would lead him up to the top of a sturdy cardboard box, where a 1 foot ruler was carefully balanced across a dowel rod across the top, with a trail of birdseed. The next morning, I found that he had snarfed up the seed along the plank and walked across the ruler past the fulcrum, causing him to fall into the box. Then he gnawed his way out. Trap 2.0 was the same except I used a 5 gallon plastic bucket. The next morning, there he was in the bucket. I took him far away and let him go in the woods. Note that this will be contrary to the law in many jurisdictions. If you just take him outside, he will probably be back inside before you are. Edison 16:08, 16 May 2007 (UTC)

Humane mouse traps are really easy to make: http://www.smithsax.btinternet.co.uk/products.htm ...for example. Trap the mouse - drive a mile from your home and release it someplace. Pet mice are so cheap that our local pet store gives them away for free when you buy a mouse cage. That way you'll know it's healthy - and hopefully not pregnant. When I was a kid, my parents bought my sister and I two pet mice (both female) - both turned out to be pregnant - we had a total of 14 baby mice within no time. Those went back to the pet store as soon as they were running round with their eyes open. Personally, I'd get a hamster - they are not social animals - they like to live alone - Mice like to live in packs and it's probably not nice for them to live alone. SteveBaker 16:56, 16 May 2007 (UTC)

And as a bonus, hamsters can dance: [4]. StuRat 23:29, 16 May 2007 (UTC)

Do you have any idea how many years of intensive therapy it's taken to get that damned tune out of my head? Now it's right back in there again. My lawyers will be in touch! :-P SteveBaker 23:48, 16 May 2007 (UTC)

This may help somewhat. --Kurt Shaped Box 23:56, 16 May 2007 (UTC)