Wikipedia:Reference desk/Archives/Science/2011 April 10

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April 10

Is there and hand-powered or foot-powered laptop charger?

XO-1 clamp charger. If you had an OLPC XO-1 laptop, you could use this hand-crank. I'm not sure it'd be practical to be cranking on this thing in economy-class, though. APL (talk) 03:42, 10 April 2011 (UTC)

Whenever I go to anyplace far from a plug outlet (like some campgrounds or an economy-class section of an airline), a thought I always have is "Are there any manually-powered laptop chargers anywhere on Earth?"

Now I hope you can solve this thought once and for all. Where would I find those kinds of chargers? (By the way, it would help me lose weight.) --70.179.169.115 (talk) 21:35, 9 April 2011 (UTC)

I think that the electricity requirements for a laptop are a bit too high for that to be practical. Maybe one with a tiny screen and a stationary-bicycle-type charger might work, but that wouldn't be very portable. Perhaps multiple pre-charged batteries would be more practical, although airlines might not like those.StuRat (talk) 22:01, 9 April 2011 (UTC)

A minute on a stationary bike will get you about 5 minutes of laptop power (assuming 100 W from biking and 20 W as a typical laptop power drain for CPU-light activities). OLPC has specialized laptops that can be powered by a hand-crank for the developing world, but they've gotten down to only 2 W under normal usage. Dragons flight (talk) 22:17, 9 April 2011 (UTC)

Well apparently power requirements have improved, because I distinctively remember doing this thought experiment in physics class in 2000 (yes, I'm old), It was an Apple desktop from the early nineties. In any case, only one person in class was fit enough so as to even get the computer through bootup (which -as you other old folks might know - was pretty freaking long for early 90s Apples). Magog the Ogre (talk) 03:20, 10 April 2011 (UTC)

Um, holy shit, if taking physics in the early 2000's is old, what does that make me who was teaching physics in the early 2000's? --Jayron32 03:52, 10 April 2011 (UTC)

All these kids with their technology... why, back in my day we used Windows Vista! And us old-fogeys still knew how to make a computer run smoothly, even though we had to fit all our programs into a mere 1 gigabyte of RAM! Nobody ever complained about battery-life either, because we still plugged the computer into the wall! Nimur (talk) 19:39, 10 April 2011 (UTC)

We never had a wall, a wall would have been luxury to us. if we wanted to divide 3200 by 365 we had to double 365 repeatedly until the largest possible multiple of 365 was reached, which is smaller than 3200. In this case 8 times 365 is 2920 and further addition of multiples of 365 would clearly give a value greater than 3200. Next we noted that (2 / 3 1 / 10 1 / 2190) times 365 gives us the value of 280 we needed. Hence we found that 3200 divided by 365 must equal 8 2 / 3 1 / 10 1 / 2190 (ref). Cuddlyable3 (talk) 12:30, 11 April 2011 (UTC)

Not practical for flying, but on camping grounds you could use a solar charger - although I have never used one and have no idea how well they actually work -- Ferkelparade π 03:28, 10 April 2011 (UTC)

Mars Science Laboratory landing criteria

This news article discussing the landing criteria for the Mars Science Laboratory says: Being nuclear-powered, Curiosity cannot go to a location that has either water or ice within one meter of the surface, Golombek noted, due to planetary protection guidelines. What is the basis for this guideline and what then is the purpose of Curiosity's DAN instrument? Are they hoping to find what they are trying to avoid? -- 110.49.234.239 (talk) 00:38, 10 April 2011 (UTC)

I haven't been able to confirm that claim on any sites with a better reputation for science reporting than msnbc, so I wonder if it's even true (in the rest of the article, they gave exact quotes from this Golembek, but not in that paragraph, so it is possible they misunderstood). It is important to note that "nuclear-powered" really isn't a good description. There is no nuclear reactor, there is a radioisotope thermoelectric generator. That's just a lump of radioactive material giving off heat as it decays and that heat is turned into electricity to power the lander. The risk from the radioactivity is fairly low. --Tango (talk) 11:31, 10 April 2011 (UTC)

I wonder if it was an unfortunate collision of two unrelated sentences - the "planetary protection" thing is generally a biological concern. Though it seems rather absurd, considering my impression that any given Mars probe is, in all probability, going to end up smashed all over the landscape. Wnt (talk) 15:59, 10 April 2011 (UTC)

By "in all probability", did you mean "as likely as not", given the historical success rate of Mars landings and orbital insertions? -- 110.49.248.162 (talk) 23:37, 10 April 2011 (UTC)

Heh, we have an article for that? Well, a 50% success rate is better than I thought, and some of those are launch failures that won't touch Mars. Wnt (talk) 02:11, 11 April 2011 (UTC)

Here the answer from a real planetary protector! (no this is not a joke) The problem wit the RTG is that it produces heat. After a crash landing the heat and the subsurface ice would form a habitable zone. Any microbe on the rover outside might find enough food to grow and than you have a small area which is full of evolving earth life. This would rendering any further mission to Mars useless because you find earth based life and not Matian life. Areas where this can happen are listed as special regions and belong in a special category for missions. So MSL is not designed to reach special regions as a whole, only the small drilling tool is sterile and might be clean enough to touch a special region. As a crash landing is possible they are not allowed to land in an area with possible special regions. They will drive to the interesting places, they have the lifetime to do so.--Stone (talk) 19:25, 11 April 2011 (UTC)

Sound in space

What would be the implications if it were possible for sound to propagate in space? Would it be possible to hear hellish supernovae explosions and other stuff?--89.76.224.253 (talk) 01:20, 10 April 2011 (UTC)

Eh. First, interjecting something like Earth's atmosphere into the interstellar medium would have wide-reaching effects such that whether or not we heard a distant supernova wouldn't be terribly significant (for instance, we'd collapse into a black hole in pretty short order). Generally, though, I think it's a fairly safe principle to derive from how light behaves: supernovae may objectively be hellishly bright, but they're so far away that they are not subjectively bright. Sound will have a similar rate of dissipation (the same in ideal conditions, probably higher in terms of power lost to the medium), and so I feel pretty confident that supernovae wouldn't be subjectively loud, either. As with light, the sun would probably dominate the local soundscape.

On the other hand, if you don't like putting an actual sound transmission medium in place and are instead just asking "but what if we could hear through space?", then you're rewriting physical laws and the answer can be more or less what you like. — Lomn 03:12, 10 April 2011 (UTC)

In the most broad definitions of "sound" and "space", you can technically make a sound in space, but there are real physical limits to the property of that sound. The basic principle is that sound may only propagate if the molecules doing the propagation are close enough together. The exact minimum spacing of the molecules is dependent on the desired frequency of the sound, or if you prefer to think of it the other way, there is a minimum frequency of sound which may be transmitted by any medium, and that minimum frequency is dependent on how close together the molecules of the medium are. This relationship doesn't have a bounds to it; so hypothetically you could generate a sound even in a medium where the molecules were spaced kilometers apart, if, for example, the sound wave was similarly huge, say millions of kilometers in wavelength. That's a fairly low-frequency sound, but its still a sound. So yes, you can generate a "sound" in "space", but you cannot generate a sound which human ears (or indeed, any means of sound detection we have on earth, be they natural or artificial) could detect. --Jayron32 05:32, 10 April 2011 (UTC)

Indeed, there are even real, measureable consequences to the speed of sound in space. The termination shock, for instance, occurs at a point about 80 AU from the Sun where the solar wind is slowed by its interaction with the thin stuff in space to a subsonic speed (about 100 km/s); this results in measurable local compression and heating. TenOfAllTrades(talk) 19:37, 10 April 2011 (UTC)

Of course, the word "local" needs to be interpreted relative to the size of the wavelength involved. The termination shock is sort of a "region" with extent on the order of AUs. When Voyager II passed through the heliopause, the astrophysical community debated the actual timing of the crossing over a span of several years. (There are still some scientists who believe that the relevant instrument readings are at levels that indicate Voyager II is still inside the heliosphere). It's a bit difficult to intuit, but you have to think of a boundary zone whose size is determined by the effective wavelength - which is enormously huge. See our article Heliosphere#Heliopause, and especially the section about detecting the effects. The "sonic shock" is measured as a gradual decrease in particle density (from "almost-total-vacuum" to "almost-completely-totally-vacuum"), accompanied by an effective difference in average particle incidence energy. But, if you were to draw a diagram scaled by the relevant scale-length, this hundreds-of-millions-of-miles-wide zone would be a "clean" boundary line between solar heliosphere and interplanetary space. Nimur (talk) 19:50, 10 April 2011 (UTC)

Question: for a sound as long as Jayron is proposing: wouldn't we eventually hit some sort of limit to the length of the wave? I simply cannot fathom that a wave could exist with a length of millions of kilometers. My knowledge of physics is not good enough to answer any of the following, so I'm asking for clarification:

1. Would it require an obscene amount of energy to produce such a wave, one that humans cannot produce, in order to try to monitor this possibility?
2. Would Planck's law in some way require that the length of the wave be an intermediary length, for which the desired distance is simply too long?
3. Even if the above concerns were somehow addressed, isn't sound based off of molecules getting close enough to each other to interact on an electromagnetic basis (i.e., they bump into each other)? Thus the precision required for having one molecule hit another at such a distance is outstandingly high, correct? I suppose it wouldn't be an issue if there was a flood of molecules, e.g., a supernova which somehow created low frequency sound. Magog the Ogre (talk) 20:41, 10 April 2011 (UTC)

1. I don't see that there would be any clear lower limit to the energy of such a wave. It might be hard to detect such waves no matter what their energy are, but that's a different matter from whether they can exist.

2. Um, why would it?

3. True, at least in areas of interstellar space where the matter is not ionized. Within the galactic disk, there's usually not more than a few centimeters between neighboring atoms, but they hardly ever hit each other. That is why the wavelengths have to be that large, because the wavelength needs to be many times the mean free path before a wave can propagate. –Henning Makholm (talk) 21:25, 10 April 2011 (UTC)

Theoretically, there's no reason you can't have a wavelength of light-years. Practically, we have to ask: what transducer could be so large that it could radiate that low frequency? You would literally need a vibrating membrane the size of the galactic disc. As such, it's best to think about these waveforms as wave-like descriptions of the material in the galactic disc, rather than as a propagating sonic "signal." The size- and time-scales relevant to such waves are cosmological in scope, so this analysis might actually be useful for analyzing galactic formation and early universe cosmology. For example, density wave theory explains one such formalization. Nimur (talk) 22:17, 10 April 2011 (UTC)

It is probably worth noting for interest sake, that prior to decoupling, indeed sound was the only way that information could propagate significant distances through the universe. —Preceding unsigned comment added by 92.20.198.146 (talk) 01:33, 11 April 2011 (UTC)

Question about the lightcone?

As we all know that when a flash of light is released from source, light-rays spread out isotropically in space, tracing out a cone on a space-time diagram. As "cone" is expanded at the speed of light, and light emitted at the apex and moves on the surface of the cone, therefore, at any instant “t” say one light second, the radius, edge and the vertical axis of cone represent a right angle triangle in which

Vertical axis is the perpendicular of triangle = t = time

Edge of the cone is the hypotenuse of triangle = st = space-time diagram of a pulse in one second

Radius of cone is the base of triangle = c = speed of light in one second

Thus c² t² = (st)², where (st) > c, so is this possible?

Q1: Why the space-time diagram [edge of light-cone/ light like curve] of light in light cone is greater than speed of light?

Similarly, nothing can travel at or greater than the speed of light therefore

Q2: How come space forward in time in its space-time diagram [upward direction] at the speed of light? [Space include we all including nature at present]

Q3: Is light forwards in time in two directions horizontally [moves on the surface of cone] as well as vertically [upward direction in time] ?

Q4: Isn’t time dilating even in a stationary light clock because a pulse covered a greater distance in its space-time diagram?68.147.41.231 (talk) 02:46, 10 April 2011 (UTC)Eclectic Eccentric Khattak #1

The quantity you call "st" has no physical meaning. The geometry of spacetime does not follow the Pythagorean formula (you can stick numbers into it if you want, of course, but the result will not have any physical meaning). What one must use instead is

$s^{2}=t^{2}-x^{2}$

where x is the distance, t is the time coordinate, and s is something called the space-time interval. It is always 0 between two events connected by a lightspeed path.

If I understand your numbered questions correctly, they are all mooted by this initial misunderstanding. –Henning Makholm (talk) 03:08, 10 April 2011 (UTC)

Hennings equation above assumes c=1. for more general choice of units you should have :: $s^{2}=(ct)^{2}-x^{2}$

The basic error is the statement that nothing can travel faster than the speed of light. The physics of relativity only assert that no physical object can move faster than the speed of light. Abstract events don't obey any speed limit. Looie496 (talk) 03:12, 10 April 2011 (UTC)

Not quite, causality requires that no information can travel faster than the speed of light. This is much more restrictive than applying the rule to merely physical objects. —Preceding unsigned comment added by 92.20.198.146 (talk) 01:38, 11 April 2011 (UTC)

Carburator.......mystry......

hi... I know the basic functioning of a normal carburator(generally used in single cylinder 4 stroke motorcycle).....but have some doubts... as i know when vehicle is in nutral gear (idling condition)it needs rich mixture of air and fuel and at the same time throttling valve is in fully closed condition. when we drive uphill it needs more fuel and when we drive downhill it needs less fuel.

I want to know that when we drive down the hill and if motorcycle is in top gear and we put throttling valve in close condition (as in idling condition), will it consume more fuel than normally driving with throttling valve in open condition. —Preceding unsigned comment added by 220.225.96.217 (talk) 03:39, 10 April 2011 (UTC)

You want to know if the vehicle uses more fuel coasting with closed throttle than normal driving (with throttle partially open). That, is more complicated than it ought to be, since carburetors have gotten more complicated. (Let's assume the same speed in both cases)

Obviously, coasting itself doesn't require input of energy the way normal driving does. Closed throttle, however, generates a large degree of drag. But, if you are actually coasting with actually closed throttle at that fixed speed, then the acceleration from gravity must by definition be larger than the drag of the closed throttle, so theoretically you would need no fuel, even to keep the engine turning, since gravity is doing that. In practice, there are complications: crude old carburetors will suck a lot of fuel with the throttle closed under these conditions but not burn it because the air is shut off, because the throttle shuts down the air but the fuel is sucked through the idle passages which open below the throttle and they now see a big vacuum . You see this in race cars decelerating, for instance, when big flames come out of the exhaust when the hot unburned fuel hits the open air. But modern carbs may have gimmicks to cut that out, to reduce fuel consumption, to reduce emissions, and to stop raw fuel being poured into the catalytic converter overheating it. For instance the throttle might be rigged (electronically, for instance) to not close all the way when speed is nonzero, thus reducing the vacuum that sucks the gas through the idle passages. Alternately, all those air passages and bleed holes and what not in the carb might serve to reduce idle fuel flow when vacuum is super high, as when coasting compared to idling.

So, to sum up, the answer to your question would be, the vehicle wouldn't "use" any fuel when coasting but a simple carburetor may waste quite a bit, if you want to draw the line between using fuel and wasting it; whether it would waste more than it would need while driving on the flat depends on a million things such as, obviously, speed and the steepness of the slope, for two. However, more complicated carburetors can be designed to waste less fuel in these conditions. This probably doesn't actually answer what you want to know at all. Gzuckier (talk) 04:20, 10 April 2011 (UTC)

Throttle valves never close. At idle the throttle is slightly open, as set by an idle screw, and fuel enters the air stream from a small jet. If the vehicle is in gear and rolling down a hill in idle, more air and fuel are sucked in but the extra fuel is wasted because the idle arrangement is not dimensioned to give the stoichiometric gasoline-to-air ratio 14.7 However the amount of fuel involved is small. When the throttle is opened two things happen: A) an accelerator jet briefly injects extra fuel. This occasionally produces an over-rich mixture so some fuel can be considered "wasted" but only briefly, and B) the main fuel jet(s) come into play when the throttle is open and much more fuel is consumed. Whether any is wasted depends on whether the carb is adjusted to deliver a richer than stoicchiometric mixture. See the Wikipedia article Carburetor. Cuddlyable3 (talk) 11:04, 10 April 2011 (UTC)

how are methane and CO2 greenhouse gases?

On the basis of polarity, that is. I understand how H2O is a greenhouse gas, while O2 and N2 aren't, on the grounds of H2O's notorious polarity, but CO2 is symmetrical. I'm totally guessing that it's the internal polarities of the CO double bonds that might do it, but then were does methane come in? Not only is it symmetric, but isn't the CH bond pretty nonpolar? Gzuckier (talk) 04:03, 10 April 2011 (UTC)

An informative discussion can actually be found at a related article to the greenhouse effect, namely Infrared_spectroscopy#Number_of_vibrational_modes. IR spectroscopy and the greenhouse effect work on the exact same principle; the ability of a molecule to absorb energy in the infrared region of the spectrum. Infrared absorbtion is associated certain types of molecular vibrations that are active in the in the absorbtion (and in the greenhouse effect especially) re-emission of infrared photons. The specific effect that governs how CO2 works as a greenhouse gas is called the Renner–Teller effect, that article is very jargon-laden and inaccessible to the average reader, however to break it down simply, CO2 has the ability to vibrate assymetricly, that is you can get vibrations where one C=O bond is shortening and the other C=O bond is lengthening. This mode of vibration is (called "wagging" in the Infrared spectroscopy article) is exactly why otherwise symmetrical molecules exhibit IR-dependent absorbtions and emissions. Since two-atom molecules cannot "wag" like this, they are invisible to IR. Three-atom molecules are the smallest molecules which have this mode of vibration, and so they are capable of absorbing infrared radiation, and thus have the ability to cause a greenhouse effect. If you look at Atmosphere_of_Earth#Composition, you'll see that the two most abundant gas you'll find in dry air, which have at least 3 atoms, are CO2 and CH4. --Jayron32 04:50, 10 April 2011 (UTC)

Oh, and regarding Methane and the C-H bond; the C-H bond isn't nonpolar, its just that the bonding symmetries present in hydrocarbons make hydrocarbons as a molecule nonpolar. CH4 is a nonpolar molecule for the same reason that CO2 is, the dipoles present in the molecule all cancel out. Some basic trigonometry will prove that to you. In even more complex hydrocarbons, all relevent C-H dipoles almost always end up cancelling, which is why hydrocarbons, even really complex ones, end up being non-polar. --Jayron32 04:58, 10 April 2011 (UTC)

what kind of spider is this black one with a red butt?

What kind of spider is this? I found it in my backyard in Richmond, California This is in the San Francisco Bay Area. She was black but not jet black very slightly almost fuzzy looking with an oblong red butt almost brick colored. She seemed to like the shade.Thisbites (talk) 04:47, 10 April 2011 (UTC)

I live in the SF Bay Area and I've seen lots of these. It's a jumping spider, possibly Phidippus johnsoni or Phidippus californicus. -- BenRG (talk) 06:56, 10 April 2011 (UTC)

Salticidae are quite amazing spiders. They have extremely good eyesight, and use advanced hunting techniques. Whenever they come up here, I like to post this excellent article [1]. SemanticMantis (talk) 15:00, 10 April 2011 (UTC)

What is the best store-bought equipment to clean soot out of the fireplace walls?

Since soot seems incredibly hard to clean out of the fireplace brick wall, what would be some equipment needed to do it adequately?

Sand blaster. Cuddlyable3 (talk) 10:37, 10 April 2011 (UTC)

Calories burned from cleaning fireplaces

Also, since I prefer to lose weight by doing chores for others, I wonder how many calories per hour (or 10 minutes) I would burn by cleaning out a fireplace. Some suggested that I run instead, but it doesn't help anyone else like cleaning a fireplace would, nor is that as fun as exercising on an XBox Kinect or zipping to class on a bike.

On the other hand, how many calories get burned from jogging at 5 MPH?--70.179.169.115 (talk) 04:50, 10 April 2011 (UTC)

Note: The OP has a long history of asking pointless/trolling questions on the ref desks. Looie496 (talk) 05:17, 10 April 2011 (UTC)

There is no way for us to know how much of your body you'll use. Probably akin to playing tennis or something, if you go at a high speed. Just try it out and compare it. Magog the Ogre (talk) 20:46, 10 April 2011 (UTC)

Calories per pound?

I never got around to finding out how many calories are in one pound of body weight. When you state the answer, please also cite the source. Thanks! --70.179.169.115 (talk) 04:50, 10 April 2011 (UTC)

Are we talking about the human body ? The would depend on how much flesh they have, especially body fat, since it has the most calories per pound, followed by protein, with bone and water having basically zero calories. StuRat (talk) 04:57, 10 April 2011 (UTC)

If it helps anything, I weigh ~195, and am 5'11.5". Would that bring us closer to figuring out how many calories I'd need to burn to lose 14 lbs? 182 is the overweight threshold, so I'll "finish" once I weigh 181. Thanks. --70.179.169.115 (talk) 05:11, 10 April 2011 (UTC)

To the OP: Are you asking "How many dietary calories will I get from eating person" or are you asking "How many calories do I have to "burn" to lose 1 pound of body weight". The first question is pretty simple to answer; the edible parts of you are essentially all protein and fat, protein will provide 4.1 calories/gram and fat will provide 9.4 calories/gram of food energy, see the table at Food_energy#Nutrition_labels. If you can work out how much fat and protein are in your body, you can figure out how many food calories you can provide (presumably to someone else, since autocanibalism is rarely a long-term survival strategy). If you want the second question answered, its really impossible to answer even in very broad terms. The amount of calories you burn doing various activities, AND the effect of burning those calories on your body weight, are really uniquely dependent on you and own body chemistry. It is a complex melange of Basal metabolic rate, Body Mass Index, your own muscle mass, your own unique muscle composition (such as the ratio of fast twitch/slow twitch type muscle fibers, see Skeletal_muscle#Muscle_fibers, how active or sedentary you are, your base heart rate, etc. etc. Its way too complicated to say, for you specifically "If I run ten miles, how many calories will I burn" or "If I burn XXX calories, how much weight will I lose". You can, of course, do the experiment, and say calculate a ratio of activity levels to weight loss, but you will quickly find that the relationship is dynamic and feeds back on itself; i.e. as you work out, you actually affect how fast you lose weight, and it isn't even easy to predict how the changes themselves will change, i.e. as you work out, you change your basal metabolic rate, which means you may lose more weight; but you will also build muscle mass, which will conversely cause you to gain some weight. Its a complete and utter mess working out the specific numbers. We can speak in general trends; i.e. if you consume less food calories and you are more active, you will tend to be healthier and have more positive health outcomes (irrespective of your weight) and the reverse is also generally true. --Jayron32 05:11, 10 April 2011 (UTC)

The IP asking this question has a history of ref-desk trolling, it should be noted. Looie496 (talk) 05:18, 10 April 2011 (UTC)

I dunno, these seem like legitimate, answerable questions. The questions themselves do not seem to beg for controversial answers, nor are they in-and-of-themselves disruptive. The IP address may have asked disruptive questions in the past, but I see no reason not to answer these questions for that reason. I am will to extend good faith so long as the questions themselves are benign. --Jayron32 05:24, 10 April 2011 (UTC)

are there calories in water?

i know calories are something measure by something making a drop of water go up by one degree, so water has a tiny amount of calories right?Thisbites (talk) 04:58, 10 April 2011 (UTC)

No, pure water will have zero calories, meaning you don't get any heat produced from it by burning it. StuRat (talk) 05:00, 10 April 2011 (UTC)

No, you're both sorta wrong. A calorie is just a unit of energy, like a Joule. In fact there are 4.184 chemical calories in a joule, or 4.184 food calories in a kilojoule 4.184 joules in a chemical calorie, or 4.184 kilojoules in a food calorie. The way a calorie was originally defined was the energy needed to raise the temperature of water (1 gram for a chemical calorie, and 1 kilogram for a food calorie) from 24.5 degrees celsius to 25.5 degrees celsius, but we now define it more rigorously by relationship to the Joule, and thus from the base definitions of the SI system. The choice of water is arbitrary, and has nothing to do with the energy in the water, or the energy you can get from "burning" water, or anything else having to do with water. Its just a unit, used to measure energy/work, and that is all. In other words, the "Calorie" unit has no more connection to water than the "foot" as a unit has a connection to actual feet, excepting as a historical definition. Also, you can burn water, in the sense that if you put enough heat energy into it, you can cause it to change chemically into hydrogen gas and oxygen gas; this is what happened in the Fukushima I nuclear accidents; the extreme heat of the uncontrolled reactors basically "burned" the water, releasing hydrogen and causing explosions which damaged the plant. --Jayron32 05:21, 10 April 2011 (UTC)

Your conversion factors are the wrong way - it's 4.18 joules in a calorie. Zain Ebrahim (talk) 12:54, 10 April 2011 (UTC)

fixed --Jayron32 17:46, 10 April 2011 (UTC)

It seems to me the original poster is more or less correct. If you're on a calorie-counting diet, you may as well say that a liter of water at 10°C has 10 more (kilo)calories than a liter of water at 0°C, since the body has to burn an extra 10 kcal to heat the latter up to body temperature. Although they both have negative calories overall. -- BenRG (talk) 06:43, 10 April 2011 (UTC)

Our articles related to the power-plant hydrogen explosions, supported by refs, state that the hydrogen comes from water undergoing redox with zirconium metal, not pyrolysis of water itself. DMacks (talk) 10:12, 10 April 2011 (UTC)

The disassociation of water is endothermic (absorbs more energy that it releases), so it can't be described as "burning". Burning refers to combustion, which is defined, in part, as an exothermic reaction (releases more energy than it absorbs). --Tango (talk) 11:37, 10 April 2011 (UTC)

The notion that you can burn water is a little silly. Any substance can be disassociated into its constituent atoms at a high enough temperature. In the case of water this does not amount to burning, more energy has to be put into the system to cause disassociation than is released. This is clear from the large amount of energy that is released when the opposite reaction - the burning of mixed hydrogen and oxygen gases - produces water as an end product. The answer to the OPs question is a simple "no" - water does not contain any dietary calories. SpinningSpark 09:08, 10 April 2011 (UTC)

You can burn water just fine. It's simply a matter of finding a more powerful oxidizer than oxygen: I've heard that chlorine trifluoride works well. --Carnildo (talk) 22:53, 13 April 2011 (UTC)

OK, let me clarify my response:

A) Do you gain any calories by consuming water ? No, unless you consider that drinking hot water may mean you can burn less food to maintain proper body temperature.

B) Can water contain energy in the form of heat ? Yes, and this energy can be measured in calories or other units. StuRat (talk) 06:59, 10 April 2011 (UTC)

While the OP's question has been answered (there are no dietary calories in water), it is still interesting to consider some theoretical limits of using pure water as an energy source. If I have one kg of water at room temperature and the relative humidity is, say, 50%, then the water will evaporate all by itself: The Gibbs energy of the 1 kg of water is more than that of the water vapor. So, I can extract work from pure water, and it isn't difficult to compute how much. However, the maximum power that one can extract is, I think, not so easy to compute. I guess there is no hard theoretical limit to this, you can think of making the evaporation rate arbitrarily high by using larger and larger surfaces... Count Iblis (talk) 16:53, 10 April 2011 (UTC)

Evaporative cooling like this, that is using water spread over large surface areas, is a common enough; the work you do in evaporation is essentially work you do in cooling (i.e. removing heat from) something; in the Old South of the U.S., prior to air conditioning, it was common to sleep with wet sheets; the evaporation of the water from the sheets kept the sleeper cooler than dry sheets would. --Jayron32 17:50, 10 April 2011 (UTC)

Yes, it's an effective way to keep cool. Count Iblis (talk) 17:03, 11 April 2011 (UTC)

Water can interfere with the intake of calories from food, see here. Count Iblis (talk) 17:03, 11 April 2011 (UTC)

Energy source graph

I remember seeing on Wikipedia a line graph showing how the percentages of the amount of energy by source used by the muscles vary with hours of exercise, in red/orange/yellow, but can't seem to find it anymore. Can anyone help? Thank you 85.138.123.142 (talk) —Preceding undated comment added 08:20, 10 April 2011 (UTC).

I believe I know the type of diagram you mean, and I can't find one on WP either(yet). Here is an external link to some graphs.
The 'sources' being in this case Aerobic respiration, Anaerobic respiration and ATP-PC biological energy systems. - 220.101 talk^\Contribs 12:00, 10 April 2011 (UTC)

Canine teeth and monkeys

If herbivores generally don't have canine teeth and if humans evolved from herbivore monkeys, what caused humans to gain such teeth?--89.76.224.253 (talk) 13:10, 10 April 2011 (UTC)

What makes you think that herbivores don't have canine teeth? DuncanHill (talk) 13:18, 10 April 2011 (UTC)

Check out the fearsome canines on baboons here [2]. SemanticMantis (talk) 14:29, 10 April 2011 (UTC)

It's not accurate to say that humans evolved from monkeys. more that primates (including humans) had common ancestors. Actually the predominance of cannine teeth is one of the more important factors in distinguishing the line of hominids to humans. Earlier hominids had much larger canines. There's a lot of evidence that most of our ancestors were definitely not herbivores.190.56.14.159 (talk) 13:58, 10 April 2011 (UTC)

What makes you think monkeys are herbivores? With very few exceptions, primates are omnivores. Of all the primates humans have the most "degenerate" canine teeth. A leading theory to explain it is the idea that our ability to prepare our food manually before eating has allowed our teeth and jaws to reduce. Roger (talk) 15:45, 10 April 2011 (UTC)

Canine teeth are useful for fighting as well as prey capture -- rhesus macaques are almost exclusively vegetarian and they have pretty fearsome canines -- I have a scar to prove it. Baboons, by the way, are definitely omnivores -- they will even prey on other types of monkeys if they can catch them. Looie496 (talk) 16:19, 10 April 2011 (UTC)

This does raise a question in my mind. We've all seen movies of chimps preying on monkeys, but (other than insects),are there any documented instances where monkies/apes have been feeding on more common food species like small rodents etc.190.56.16.100 (talk) 16:57, 10 April 2011 (UTC)

If they only prey on monkeys, then perhaps it has less to with food sauce and more to do with dominance over competitors for food.190.56.16.100 (talk) 17:08, 10 April 2011 (UTC)

There are many reports of monkeys preying on small mammals, birds, lizards, etc. I'm not going to take the time to look up sources, but they wouldn't be difficult to find. (Our baboon article gives some information along with a reference.) Looie496 (talk) 17:18, 10 April 2011 (UTC)

I believe one factor in the diminished size of human canines is that they are no longer used as weapons, since we developed more useful external weapons (rocks, spears, arrows, etc.). StuRat (talk) 17:10, 10 April 2011 (UTC)

A prim Victorian lady was heard to say "I don't know whether Mr. Darwin is correct to say that humans have chimpanzees as ancestors, but if he is right then I hope it does not become widely known." Cuddlyable3 (talk) 10:32, 11 April 2011 (UTC)

Electron resonance and tapping

Say if a electron orbiting inside of a magnetic field gets hit by a wave with the same frequency as the electrons circular frequency. Could the electrons be made to make a electrical current flow with their new energy. —Preceding unsigned comment added by 82.38.96.241 (talk) 18:04, 10 April 2011 (UTC)

Isn't that close to what generators do. (details not withstanding).190.56.16.100 (talk) 19:32, 10 April 2011 (UTC)

I don't really understand the idea underlying the question, but the concept of stimulated emission may be at least vaguely related. Looie496 (talk) 19:42, 10 April 2011 (UTC)

Based on the OP's prior questions, I'm pretty sure he is asking about Electron cyclotron resonance.

The electron orbit is already a current. Any change in the electron energy, due to incident radiation or any other source of energy, will cause a corresponding change in both the magnitude and the vector of the current. You might want to read about current density for a proper overview of a three-dimensional mathematical description of current. Interactions between radio-waves and gyro-resonant electrons are very complicated. Nimur (talk) 20:36, 10 April 2011 (UTC)

Fog

I notice yesterday in the sky a weird type of fog. it was quite brownish yellow kind of colour. It was also quite high in the sky and didn't look like any cloud formation I ever have seen. What was it. --109.76.36.208 (talk) 18:53, 10 April 2011 (UTC)

Were you in L.A? Mexico city? etc190.56.16.100 (talk) 19:35, 10 April 2011 (UTC)

Sounds like smog, perhaps a fire provided the smoke ? If you give us your location, we will look for fires in your area. StuRat (talk) 19:38, 10 April 2011 (UTC)

I was going to say that it might be the current "worst ever" Texas wildfires,^[3] but that IP geolocates to Dublin. The smoke couldn't go that far... could it? Wnt (talk) 02:16, 11 April 2011 (UTC)

No im down here in Cork if that helps. --109.76.7.143 (talk) 15:07, 11 April 2011 (UTC)

I couldn't find any news of a big fire there. Could it be pollution from a factory in Cork ? Or perhaps from the port or airport ? The color you describe makes me think of sulfur. Did you notice a "rotten eggs" smell that day ? StuRat (talk) 07:20, 12 April 2011 (UTC)

Chemical bonding

Is there any compound with a P-S-H bond? Nirmos (talk) 20:01, 10 April 2011 (UTC)

Yep. (Among several other dithiophosphates.) TenOfAllTrades(talk) 20:13, 10 April 2011 (UTC)

Thank you so much! Nirmos (talk) 20:24, 10 April 2011 (UTC)

Electron configuration orbitals

If nobody has ever actually seen an atom, how do they know that after all the 3p orbitals are filled, the next orbitals are 4s instead of 3d? If the answers to this question reference spectral lines as the indicator, how does the position of a line on the electromagnetic spectrum tell you that the shape of the next electron cloud density is spherical and not butterfly shaped? 76.27.175.80 (talk) 21:18, 10 April 2011 (UTC)

I'm no expert on this, but the shape of orbitals is determined mathematically by solving the wave function- not by "actually seeing" it. Staecker (talk) 01:25, 11 April 2011 (UTC)

My gosh you're certainly not a scientist, are you a mathematician by any chance? To contradict the previous poster, in physics we like to find out if the hodge podge we concoct in mathematica has any relation to the real world, one way in which one could go about tackling this particular conundrum would be to like a the splitting of the emission spectra of atoms with the relevant number of electrons. As if indeed we are right, and after 3p we fill 4s, thus after filling 3p, if we add a further two electrons we should have filled a whole new shell, and thus since closed shells have no angular momentum this would be reflected in the spectrum. See Fine Structure, Spin–orbit interaction and Hyperfine structure for the effect of angular momentum on emission spectra. —Preceding unsigned comment added by 92.20.198.146 (talk) 01:47, 11 April 2011 (UTC)

In physics we like to understand the connection between the mathematical 'hodgepodge' and the real world. Unfortunately, this is one of the greatest problems with quantum mechanics, string theory, and the like. Quantum mechanics is accurate is describing many things, but imagining the universe as a wave function just doesn't correlate. So the wave function description is the best you can get. ManishEarth^{Talk • Stalk} 04:01, 11 April 2011 (UTC)

One of the things about the wavefunction model for orbital shapes is that the system works across disciplines to explain lots about the behavior of electrons around atoms. Various models of molecular bonding, such as valence bond theory and hybridization theory and molecular orbital theory all work nicely with the standard spdf quantum mechanical model of electron configurations because the shapes of the orbitals as described by the quantum mechanical model mesh nicely with, for example, the bonding angles predicted by hybridization theory and with behavior predicted by molecular orbital theory. And behaviors of substances generally confirm the predictions of these theories regarding molecular shape and electron organization. Just some examples:

• Bonding geometries predicted by valence bond theory and hybridization theory present molecular shapes which allow predictions of allowable and unallowable chemical reactions, for example in E2 Elimination reactions in organic chemistry, the leaving group must be able to take a specific orientation relative to the acid hydrogen in order to eliminate; this is predicted by knowing the shapes and orientations of the molecular orbitals, and confirmable by real reactions, where molecules that lack the ability to take the correct geometry do not undergo the reaction.
• Perhaps simpler to understand, molecular orbital theory predicts the O₂ to be a diradical, something not very evident from just counting the electrons. The magnetic properties of O₂ confirm its diradical nature, something which is only understandable in the context of what the quantum model predicts the organization of the electrons orbitals to be around the O₂ molecule.

So yes, we cannot "see" orbitals in the same way I can see my own hand; but that doesn't mean that they don't exist, or that the models that depend on them don't have fantastic predictive power regarding the actual properties and behavior of substances. Indeed, the entire thing is that its the predictive power of the model which makes it useful; understanding how electron configurations (and the underlying theories) works is important to understanding why the substance that makes up the world around you behaves the way it does. --Jayron32 04:49, 11 April 2011 (UTC)

Many orbitals have been visualized more directly (not "seen" obviously, but STM and related techniques), so there is fairly direct evidence for "an upper-level electron-density that matches the p dumbbell shape" on an atom expected to have p near the HOMO and "an electron-density that matches various d shapes" on atoms that have occupied d levels, etc. Spectroscopy tells you the energy levels pretty directly. The only step in the process not as easily answerable is how we match energy level (from each one's energy) to its shape--OP is on the right track that this is a more complicated analysis ("how do we know a dumbbell comes after a sphere" regardless of what energies and symbols you use to identify them). I don't have time to comment more, but figured better help distinguish some issues first. DMacks (talk) 13:08, 11 April 2011 (UTC)

Four-winged vs. two winged flight

What is more stable for powered flight in an animal, four winged or two winged? And if there was a four-winged animal, is it more efficient to have them both flapping in opposite cycles or does this create turbulence? And does anyone know of any four-winged animals, apart from insects? --T H F S W (T · C · E) 21:52, 10 April 2011 (UTC)

Am I dreaming this, or was there a Pterodactyl that had four wings (i.e. its arms *and* legs were wings)? I could swear down that I read that once... --Kurt Shaped Box (talk) 22:01, 10 April 2011 (UTC)

(EC with The High Fin Sperm Whale below)I don't think any discretely 4-winged Pterosaurs (aka Pterodactyls) are yet known: in some the flight membrane or patagium may have stretched back to rear-limb attachments, and some may have also had a further membrane between the hind limbs, similar to some Bat species.

However, some of the flying therepod dinosaurs closely related to, though not in, the Avialae clade which includes true birds, such as Microraptor, are thought from the forms of the attached feathers to have used their hind limbs as an additional pair of wings. I believe discussion of possible wing-beat patterns is ongoing in paleontological academia.

Some Flying fish glide using enlarged pelvic (rear) as well as pectoral (front) fins, but this doesn't quite qualify as powered flight, although the configuration is obviously stable. The OP might find further leads in the article Flying and gliding animals. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 22:46, 10 April 2011 (UTC)

I think I can also vaguely remember having even seen a picture of one ... but might also have been from some sci-fi. As for 2 vs. 4 wings, it is not uncommon for insects to have four wings. 77.3.170.46 (talk) 22:11, 10 April 2011 (UTC)

Not true flight, but some gliding animals use all four legs, and the skin stretched between them, like the flying squirrel and sugar glider. StuRat (talk) 22:20, 10 April 2011 (UTC)

OK, I don't think there are any that meet the description I'm looking for. But what I really want is some clue as to efficiency, stability, etc. of a four-winged creature. And do most insects fly with two seperate wing cycles or flap in unison? --T H F S W (T · C · E) 22:25, 10 April 2011 (UTC)

Can't say about all insects. That's an enormous field, but the emperor dragonfly uses four wings and they do not flap in unison. According to research each wing is individually controlled. Yes, this seems like an impossibly complex system but mother nature allways is. The muscles that do this make up fully one third of the dragons body weight and have infinitely perfect flight control. Some insects are comically clumsy in flight. there are an infinite number of variations in between. some use only two wings, some use a second pair of wings only as balancing "pendulums" or "gyros". It's an extremely wide field of study and very difficult to study. there is no simple answer to your question. You cannot simply compare insects with aircraft. carefully controlled turbulence can be an asset, as with some modern computor controled airecraft, and with some four winged insects. good luck figuring it all out.190.56.17.78 (talk) 01:02, 11 April 2011 (UTC)

Many other creatures called flying something or other (foxes, squirrels, frogs etc.) do not actually fly. They glide. pteredactyls, as mentioned, did not "according to fossils" have four wings. they had an elastic membrane stretched between the fore and aft limbs, like a bat. Again, some bats have membranes that stretch between the extremities of the limbs, in others the membrane stops short on the rear limbs. different hunting techniques. I hope that helps.190.56.17.78 (talk) 01:30, 11 April 2011 (UTC)

Insects started off with (at least) six wings (two per thoracic segment), though only two pair were large - see [4]. There are several situations in which insects have evolved from four wings to (effectively) two - (Diptera, Coleoptera, Blattodea for example, or Lepidoptera where the wings work together as one. Then again, many insect lineages lose or greatly reduce all their wings, which likely does not improve flying ability. Saying which is the best number of wings is a difficult philosophical question. Certainly dragonflies are awesome fliers, difficult even to photograph. Wnt (talk) 02:39, 11 April 2011 (UTC)