Wikipedia:Reference desk/Archives/Science/2012 July 22

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July 22

Short-term memory fading

If someone demonstrates bad short-term memory recall are there ways of improving their memory or is it a case of once its gone its gone? -- role^player 00:10, 22 July 2012 (UTC)

That's sort of a confused question. The term "short-term memory" actually comprises a number of different types of memory, with different properties. For some of them, there are ways of improving memory. However, improving memory doesn't generally mean gaining the ability to bring it back after it's gone, it means developing the ability to keep it from going away. Looie496 (talk) 00:55, 22 July 2012 (UTC)

I asked the question after reading the article short-term memory. There is nothing there about improving memory, which is why I asked. Sorry it's confusing, I thought it was a fairly simple question. -- role^player 01:03, 22 July 2012 (UTC)

Psychology books and my experience show that "rehearsal," or repetition of the entities in short term memory, aid in preserving therm far better than passively "trying to remember" them. .Show the subject a long telephone number or license plate. If the subject thinks about nothing, then the briefly presented information fades from memory in a few seconds. If the subject is given an interfering task ("Count backward by threes from 97") the fading is much faster. Now let the subject keep repeating the license plate or 10 digit number until permitted to write it , type it, or say it. The recall is amazingly better. Beyond that, there are special mnemonic techniques which would allow a person to absorb and recall masses of information. Edison (talk) 01:26, 22 July 2012 (UTC)

(ec) Ah, I've never looked at that article. The ideas it covers are actually a bit antiquated, dating back to cognitive psychology of the 1960s and 1970s. As I understand it, most people who study memory nowadays don't think that a distinct "short term memory" in that sense really exists. Anyway, the article does briefly mention the two things that are most useful in improving that sort of memory: chunking (meaning forming high-level concepts for complex clusters of information), and rehearsal (meaning focusing attention on the material you want to remember, and repeating it to yourself. Looie496 (talk) 01:27, 22 July 2012 (UTC)

It's pretty funny to read about "antiquated cognitve psychology of the 1970's" and that "short term memory doesn't exist." One memory technique is to learn a rhyme: "One is a bun, two is a shoe, three is a tree, four is is a door, five is a hive, six is sticks, seven is heaven, eight is a gate, nine is a lion, ten is a hen." It should take only a couple of repetitions and repetition trials to learn this perfectly. Then if one has to memorize ten concrete objects in order, each can be quickly associated with the noun at that position in the rhyme, by forming a vivid image of the key and the thing to be remembered. If the second thing is "honey," it is easy to remember a shoe full of honey. I. A teacher I knew had 26 such mnemonic links, one for each letter of the alphabet: "A is ape, b is bee, c is cat..." etc and could hear and recall 26 arbitrarily chosen things in a room in order. If numbers are to be remembered, there is a system for substituting consonants for digits, then remembering a concrete object for each number. One mnemonist could hear and recall 500 arbitrary three digit numbers thus. Edison (talk) 02:11, 22 July 2012 (UTC)

I didn't mean to say that there is no such thing as short term memory, just that the properties discussed in that article do not distinguish one particular type of memory that can be clearly separated from other types of memory. Looie496 (talk) 02:27, 22 July 2012 (UTC)

Alcohol and various psychotropic drugs like valium and ambien as well as marijuana and narcotics like oxycontin interfere with short term memory. Not taking them will help if taking them is a problem. One of the major benefits of marijuana is that every time you watch a movie high is the first time. μηδείς (talk) 03:32, 22 July 2012 (UTC)

Context is important to this question. Specifically the age of the person. If the individual is younger and previously fit with a good short term memory then there will be a range of causes that will different from those of a person aged, say 70+years. Whether the ability to recall recent events can be improved will depend to some extent on the cause. Some kinds of organic brain disease will cause this phenomenon, and although it may be delayed a little by therapeutic intervention its progress will be inevitable. Short term memory impairment caused by vascular shortcomings in the brain may require different therapeutic strategies and the outcome will be varied, depending on the medical abilty to resolve the circulatory problems. Some forms of new growth in certain parts of the brain may cause short term memory problems and again the ability of the medical intervention will have much influence on the final resolution of the memory difficulty. Taking psychotropic drugs can impair concentration and thus short term memory, in this group can be included many illegal mind-altering substances. If the memory is unrecallable after a short time it is possible in some circumstances to prompt a recall with clues but generally the further back an unrecalled memory slips the more difficult it will be to permanently 'imprint' it and recall it. Richard Avery (talk) 08:03, 22 July 2012 (UTC)

I have something of short term memory problem. Sometimes when people ask me what I did that morning, I have to say I can't remember, but ask me in ten years time, as my long term memory is excellent. Myles325a (talk) 08:31, 22 July 2012 (UTC)

Personally I have found marijuana only effects my memory about a fortnight to a month after stopping taking it, if I have taken a reasonably sizeable amount. Get a lot of "tip of my tongue" type stuff for a week or two. Egg Centric 16:27, 22 July 2012 (UTC)

Surprised to learn taking marijuana effects one's memory. Although there may be a difference between elephants and aardvarks. μηδείς (talk) 03:35, 23 July 2012 (UTC)

3rd order gas phase reactions - pressure limit

In elementary 3rd order reactions of the type A + B + M → AB + M and A + A + M → A₂ + M, where M is some other low affinity or inert atom or molecule, it appears from various chemistry texts that the reaction rate for any given concentration/partial pressure of A & B, increases in linear proportion to the concentration of M, up to a certain limit (the pseudo 2nd order region), which is independent of what M is. Below this limit, the rate is proportional to [A]²[M] or [A][B][M] and depends on what M is. In other words, if you plot the reaction rate against [M] for various M, you get a family of curves with more or less parallel upward slopes merging into a common horizontal line after a certain concentration [M].

What, in simple words, determines this limit? The textbooks I have don't say. The only thing I could think of is that it occurs where the concentration [M] is so high that the probability of an A+B+M or A+A+M collision is about the same as an A+A or A+B collision. But that does not seem likely, and in any case increasing the concentration of A and B would then re-eastablish a 3rd order relationship - so that cannot be it.

Second question: What happens if the concentration of A or B is increased to the same [M]-limit value, with low [M]? Does the reaction rate become 2nd order involving the concentration of M, ie [A][M] or [B][M]?

Ratbone124.182.180.91 (talk) 12:06, 22 July 2012 (UTC)

Effective power of a satellite dish turned into a solar cooker

Greetings,

If a satellite dish identical to this one is covered in standard Aluminium foil and placed in a region where the mean insolation is about 200 W/m², what would be the effective power of the resulting solar cooker? I've calculated the theoretical power expected myself, but I'm sure there are more practical bounds on the resulting power than I've taken into account. I would also be happy to hear estimates about the time it would take to boil about five litres of water with such a solar cooker, assuming that their initial temperature is about 30°C. Many thanks, ליאור • Lior (talk) 15:16, 22 July 2012 (UTC)

The dish appears to be about 4 m in diamter. Therefore the area = Πr² = 12 m² approx. So the collecting power is 12 x 200 = 2400 W = 2400 J/s. The thermal capcity of water is 4182 J/l.K and the latent heat of vaporisation at 1 Bar is 2260 kJ/l. So the required heat is [4182 x (100-30) + 2260,000] x 5 = 2,552,740 J. So the converted dish could in theory boil 5 l of water in 2,552,740/2400 seconds = 1064 seconds, ie about 18 minutes. This should be multiplied by the reflection factor of the aluminium, which can be very high, nearly unity, or very low, <<1, depnding on how well it is pollished. Your figure for insolation is very low. Most locations will be closer to 1kW/m2 if the dish is pointed correctly. On the other hand, the performance may be degraded if the dish is not made to track the sun as it moves across the sky. This problem can be largley eliminated if the hated surface is made wide enough so that the focussed hot spot allways falls on part of it. Ratbone120.145.152.248 (talk) 15:54, 22 July 2012 (UTC)

The "hated surface" ? StuRat (talk) 19:12, 22 July 2012 (UTC)

Stu, if you keep squawking about my typing, I'm gonna crawl right up your internet connection and heat you with an oxy torch. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Not complaining, I just can't tell what you meant. (You had 7 other typos, which I didn't mention, since I can figure those out on my own.) StuRat (talk) 03:39, 23 July 2012 (UTC)

Note that this 18 minute figure doesn't consider that the water will be radiating heat back out and cooling due to evaporation. The hotter it gets, the more cooling there will be. So, it will take longer to boil than that, or may only boil once much of it evaporates so the heat is concentrated on a smaller volume, or may never boil at all. StuRat (talk) 19:16, 22 July 2012 (UTC)

There are two other problems with the calculation. First, there is the factor of 5 between the 200W/m² and the more realistic 1000W/m² around noon time. Secondly, I would interpret "to boil 5l of water" as "to bring 5l of water to a boil", not "to boil it away". So the latent heat of vaporisation does not really come in. With these assumption, an ideal 4m dish can bring 5l of water to a boil in about 25 seconds under optimal conditions - much more plausible, given how fast e.g. a 2kW electric kettle will bring 2l to a boil. --Stephan Schulz (talk) 20:44, 22 July 2012 (UTC)

You are correct, he will have meant "bring to boil" - my error. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Note that aluminum foil will reflect in all directions, so you won't get anywhere near 100% pointing at the water. Also note that you'd need to rig a system to suspend the water where the cone of the satellite dish was, and hold it there, without spilling, as the dish is moved to track the Sun. You also need a way to add and retrieve the water, since, at that radius, you won't be able to reach it directly. StuRat (talk) 19:12, 22 July 2012 (UTC)

Not necessarily Stu. You can polish aluminium to a mirror finish, and it will then act as a mirror for infra-red as well. You don't need to have the dish moving to track the sun. As the cook time is only minutes, it is sufficient to make the heat surface large enough so that the focused heat always falls on it even as it moves across, as I said. This trick is sometimes done in radio communications - or the actual antenna nominally at the focal point is moved instead of moving the whole dish. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Polished aluminum would be much better, yes, but we are talking about aluminum foil here, wrinkles and all. I recommended against trying to track the Sun further down. However, to have it work at a wide range of positions of the Sun, like at the Arecibo Observatory, you need a spherical reflector, not the parabolic reflector of a satellite dish. StuRat (talk) 03:29, 23 July 2012 (UTC)

We should also ask why you want to boil the water. Is this to sterilize it ? If so, I suggest a continuous distillation system where water flows in, boils, the steam condenses, and the condensate runs off as sterile water. Ideally you would add dye to the water to make it absorb the light, but, if you don't want to do this, a dark bottomed, clear topped container will work, although not quite as well. You will need to periodically dump the water left in the container, as it will build up salt and other minerals otherwise. StuRat (talk) 19:25, 22 July 2012 (UTC)

The application is, basically, cooking in a remote village with no regular electricity. Clean water are generally available, but a clean energy source for cooking could be of use. Let's say that an Aluminum foil reflects about 80% of the incoming radiation back to the focal point. To what extent will this figure drop due to the fact that it is not applied tightly to the surface of the dish? That is, there will surely be some wrinkles that will scatter light away to other directions, rather than to the focal point. How significant will the effect of these wrinkles be, assuming that we're just manually gluing the aluminum foil to the dish? ליאור • Lior (talk) 20:16, 22 July 2012 (UTC)

I would not be too concerned about conforming exactly to the parabolic shape - reasonable care will be fine, as you don't need (nor is it desirable) to bring the focussed energy to a pin point. You only need a rougfh focus that brings nearly all the refelcted energy to the surface area of the container to be heated. Ratbone124.182.137.103 (talk) 03:10, 23 July 2012 (UTC)

Besides, this figure suggests that an average insolation of ~200 W/m² is rather typical at ground level. Is it wrong? ליאור • Lior (talk) 20:20, 22 July 2012 (UTC)

That is averaged over 24 hours. Your cooker will not cook anything at night, but will be much better at noon. --Stephan Schulz (talk) 20:32, 22 July 2012 (UTC)

I take it by "cooking" you mean food which requires cooking to be made safe to eat, like meat. I assume such food would be opaque to light, so a clear glass container, with lid, should work. I think you'll do better to cut it into small pieces first, so the heat will penetrate better. Try to minimize the amount of added water, as that will require more heat. As a practical matter, repositioning such a satellite dish as the Sun moves might be quite difficult, so you might do best to position it pointing straight up (or aimed a bit to the south, if north of the tropics, or a bit north, if south of the tropics). Cook most the food when the Sun is highest in the sky. You could possibly cook reduced quantities in the morning and afternoon, so long as no shadows fall on the satellite dish. The satellite dish will need a drain hole at the bottom.

Placing and retrieving the dish will still be difficult. You'll need something like a pizza paddle, and the grill on which the dish is placed will need a backstop to prevent the paddle from pushing the container off the grill. The weight of the food and container will be critical here, as the torque created by trying to lift a heavy load at the end of the paddle could cause you to drop it. It might also be necessary to cut an access point into the edge of the satellite dish, to enable you to get closer to the center when placing and retrieving the food.

Also note that children must be warned not to play inside the dish, when the Sun is up, as they could be burnt or blinded. Something else you should consider is that aluminum foil isn't very durable, and will likely be torn to shreds in a storm, and the expense of replacing it after every storm might be considerable. Some type of cover, or just flipping the satellite dish over when a storm approaches, might prevent such damage.

How to support the grill is another concern. Setting it on the inside of a rounded satellite dish would make it rather unsteady. You would either need to cut holes in the satellite dish for the legs to poke through to the ground, or have a system where there's a frame which extends beyond the edges of the satellite dish and down to the ground, but this might be rather heavy, making it difficult to flip the satellite dish prior to a storm.

To minimize wrinkles, the aluminum foil should be cut into thin strips, as they will more closely conform to the parabolic shape than wide sheets. I'd expect that placing the strips circularly would require less overlap than placing them radially. Also, have you considered just painting the inside of the dish with a reflective coating ? Or perhaps it's already reflective enough ? Try placing a thermometer at the focal point to see how hot it gets when pointed at the Sun. StuRat (talk) 20:47, 22 July 2012 (UTC)

Given the above calculations, you can afford quite some wrinkles. Check solar cooker to see some examples of practical designs. If you live in an area with plausible weather conditions, the average size of the collecting area is more like 1-2m². With 12m², you should be able to do with some reduced efficiency for added convenience and ease of construction. There is, e.g. no need to point the dish exactly at the sun - you can keep it at an angle that will result in the focal point not being over the dish, making access to the pot much easier. --Stephan Schulz (talk) 21:22, 22 July 2012 (UTC)

Did anyone bother to mention that a disk that shape focuses the reflected beams on the antenna propped up in front of the it, not on the surface of the dish or any water it would actually hold, due to its (it's if you are StuRat) shape, were it tilted against gravity? I mean, really, folks. μηδείς (talk) 03:26, 23 July 2012 (UTC)

When I was at school in the 1960's, we were taught that it's is the correct form when saying something like "It's going to rain today" - the apostophe signifies the missing letter from it is. The other valid form is its' - the correct form for writing "The dog wants to go for a walk and has fetched its' leash." - here the apostrophe signifies belonging - the leash belongs to the dog (similar use to "The handbag is Susan's.") The apostrophe is placed after the s in its' to distinguish it from it is. We were taught that there is no correct use of its (no aprostrophe) - however it has crept into wide use as school teaching is not to the standard it once was. Ratbone124.182.2.119 (talk) 06:52, 23 July 2012 (UTC)

I have an almost identical anecdote, except I was taught that its' is never a word and the correct form of the possessive pronoun is its (no apostrophe). I guess the standard of school teaching was never really that great to begin with. 203.27.72.5 (talk) 07:56, 23 July 2012 (UTC)

You geolocate to the same country as I (Australia), so it can't be regional differences. But you didn't give the decade you were at school. In a number of ways standards have slipped over the years. I noticed that when I went to uni 11 years after finishing school at Year 9 - kids in the same classes who had just finished Year 12 didn't know things that I did know. Ratbone124.182.2.119 (talk) 08:18, 23 July 2012 (UTC)

No two people will have exactly the same experience during their school lives and will learn different things, but there seems to be a wide spread belief that kids are learning less and less as time goes on and I just don't see it. I went to school in the 1990's in north Queensland. My older brothers went to school there in the 1980's and they didn't learn things that I did e.g. computer skills, nutrition, sex ed, Chinese mandarin. Priorities change with time, so when I went to school there was a greater focus on those things and since it all still has to fit into a 6 hour day, there had to be less time spent on calligraphy and French. When they brought in the Australian citizenship test and there was an A Current Affair segment about how immigrants shouldn't need to know, among other things, who the first prime minister was. They challenged the watchers to name him during the ad break. My girlfriend's parents, who went to school in the 1970's, my girlfriend (1990's), her younger sister (2000's) couldn't name Sir Edmund Barton. Over the years the school system has managed to fail us all equally. 203.27.72.5 (talk) 21:55, 23 July 2012 (UTC)

I did, when I said "note that you'd need to rig a system to suspend the water where the cone of the satellite dish was". StuRat (talk) 03:33, 23 July 2012 (UTC)

Is that thingy indeed called a cone? μηδείς (talk) 18:01, 23 July 2012 (UTC)

The official name seems to be a "feed horn", but I don't think that's in common use outside the industry. StuRat (talk) 22:07, 23 July 2012 (UTC)

I relieze I'm a little late on this, but I thought I'd mention this. Rob Cockerham actually built one of these with mirror tiles. I give you The Light Sharpener. I believe there's video of him using it to boil water (and burn lots of other stuff). Jerk182 (talk) 23:58, 25 July 2012 (UTC)

I think the videos are on youtube, but here's an interesting quote: "The Light Sharpener brought a quart of water to a rolling boil without a problem, in about four minutes." Jerk182 (talk) 00:05, 26 July 2012 (UTC)

Thank you very much for this link! It covers many of the efficiency and safety issues that have been bothering me. ליאור • Lior (talk) 08:25, 26 July 2012 (UTC)

Water

Has anybody ever attempted to estimate how many cubic metres of water are on the earth? For instance, if the earth's crust fragmented and all of the water poured into the mantle, would it affect the internal temperature of the earth?

The mantle is already saturated with water, dissolved in the rock. What we see on the surface is merely the excess. The crust is already fractured all over the place. Looie496 (talk) 16:03, 22 July 2012 (UTC)

According to our Wikipedia article on water, the collective mass of water found on, under, and over the surface of Earth is approximately 1,338,000,000 km3 (321,000,000 mi3). This is a mass of 1.34 x 10¹⁸ kg. Since the mass of the Earth in total is estimated at 5.97 x 10²⁴ kg, water accounts for only 0.000 02% of the total, and thus can be assumed, if it were to be somehow absorbed, to make no significant effect of the Earth's internal temperature on a thermal capacity basis. However water has a big effect on surface temperature by moderating climate and by evaporation into clouds, providing a greenhouse effect. Ratbone120.145.152.248 (talk) 16:06, 22 July 2012 (UTC)

As Looie wrote, most of the water on Earth is dissolved in the magma in the Earth's interior anyway. When the solar system just formed, there were many proto planets that collided with each other to form the present day planets. Water at the distance we are from the Sun is not stable, it will evaporate. The problem is then to explain where the water on Earth could have come from. It is now believed that some of the proto-planets that gave rise to Earth came from the outer solar system. Jupiter formed quite rapidly and it caused perturbations in the orbits of the proto planets. Some proto plantes from the outer solar system containing a lot of ice moved to the inner solar system.

The water from the proto planets ended up in the interior of the planets. This water is dissolved in the magma. Slowly this water percolated to the surface giving rise to oceans. The vast majority of all the water on Earth may thus still be in the Earth's interior. If all the water in all the Earth's oceans were removed, the oceans would slowly refill with water from the Earth's interior. Count Iblis (talk) 16:17, 22 July 2012 (UTC)

Confusion on proportional sign

I am unable to understand meaning of proportion in physics. One says x ∝ y and then writes x = ky, where k is the constant of proportionality. But what does this 'constant of proportionality' means. As in case of force, we write F ∝ ma, then we write F = kma and putting value of k = 1; we write for another time that F = ma. I am confused what is the reason behind using k. I could not understand what is the use of writing '∝'. In gravitation, we write F ∝ m₁m₂/r². Then, we write F = Gm₁m₂/r², where 'G' is constant. In the case of force, 'k' was removed but in this case 'G' itself became a part of the equation. Why is this so? What does ∝ sign mean? I am a student of 9th standard, so, don't use high level language. Please, explain me in easy language with suitable example. --Sunny Singh 16:07, 22 July 2012 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)

The convention is to write ∝ to signify that we suspect its proportional (ie varies in step), but we don't know, or haven't yet proved, what the multipying constant is.

As you have realised, the constant is not always 1 (unity). Usually in physics, we use logical reasoning to first prove the required result is directly proportional to something, proportional to the square root of something, or whatever, and then reason out or measure what the actual constant is. For example, we might suspect that the longer we heat water the hotter it will get, and the greater the heat the hotter it will get. We would state it as T ∝ Q x T / m where T is the temperature (K), Q is the heat (W/s), m is the mass (kg) and T is the time duration (seconds). We could then conduct a series of experiments, measuring these four quantities accurately. We would then find that dividing the quantity on the left, T, byt the bit on the right, Q x T / m, always gives 0.2391, i.e., our data will fit T = 0.2391 Q T / m. So now we know the constant of proportionality is in this case 0.2391, and is ALWAYS 0.2391, so we can write T = k Q T / M (where k = 0.2391).

We could suspect that water flowing in a pipe is F ∝ AP/L where L is length, F is flow rate (L/s), P is pressure (Pa), and A is the cross section area of the pipe (cm2). We could then do some experiemntal measurements. If we did, we would find the flow does indeed increase with pressure, but the multiplying factor is not constant, it varies. So, in this case we can't write F = kAP/L. We would then need to ponder it further - perhaps try a square root or an exponent somewhere.

In the SI (System Internationale), the common standard of measuring units, the units (meters, kilograms, etc) have been chosen so that the constant is in fact equal to 1 as much as possible, or if not a simple integer or pi, but often it isn't either.

Ratbone120.145.152.248 (talk) 16:13, 22 July 2012 (UTC)

Where did you see "F ∝ ma"? I think it makes no sense, for the reason you gave. -- BenRG (talk) 20:37, 22 July 2012 (UTC)

It makes more sense to say, "F ∝ a" where the constant of proportionality is the mass m. This equation is valid for most conventional non-relativistic problems. Nimur (talk) 20:50, 22 July 2012 (UTC)

Isn't that proportionality valid for relativistic problems also? 203.27.72.5 (talk) 07:31, 23 July 2012 (UTC)

Yes. But I assume Nimur was implicitly referring to rest mass, which, for non-relativistic problems is (very nearly) equal to total mass. --Stephan Schulz (talk) 07:38, 23 July 2012 (UTC)

And that is how Newton originally stated it in his second law. I don't know if he knew that the constant of proportionality was mass (he must have had a general idea that it was - it's fairly obvious from every day experience) but he didn't mention it in his statement of the law. He just stated the proportionality. --Tango (talk) 21:30, 22 July 2012 (UTC)

F = kma where k = 1 and is dimensionless is just as valid. In a different system of units (not SI), k might not be equal to 1, though an arkward system of unit it may be. However, in SI, other formulae of similar form k is not 1, but a numeric value with dimensions, as with the water heating example I gave. Ratbone124.182.137.103 (talk) 02:55, 23 July 2012 (UTC)

Why has this kid got fecal matter in his or her armpit?

If you review the article at Constipation then the very first image (i.e. in the info box) at least according to the caption has fecal matter more or less in the armpit of the child. Now presumably the caption is wrong so I plan to change it but thought I should check here, after all I'm not exactly used to X rays and may be making a stupid mistake, so... Egg Centric 16:24, 22 July 2012 (UTC)

Its not in the armpits - notice it is at the position of the lowest ribs. Small children have comparitively small chests relative to their abdomen. So the poo has accumulated at the top corner of the large intestine (ie where it does a right angle turn). Ratbone120.145.152.248 (talk) 16:33, 22 July 2012 (UTC)

Does this child have a freakishly tall abdomen? Egg Centric 21:04, 22 July 2012 (UTC)

No. You seem to be reading the X-ray wrong. Their shoulders are well off the top and the bottom of their ribs are right where they should be. StuRat (talk) 22:00, 22 July 2012 (UTC)

You're right. I've found a few x-rays of complete skeletons and counted the verterbrae. It's very peculiar to me though how small the hip turns out to be. Just on the offchance is this likely an example of systematic "delusion" or is it something idiosyncratic to how I perceived the body? Egg Centric 23:36, 22 July 2012 (UTC)

What you probably mean is how small the hip bones are. The actual hips are larger, since they have muscle, fat, and skin on top. Skeletons, by their nature, always seem "skinny". StuRat (talk) 00:36, 23 July 2012 (UTC)

Working of rockets

Can you explain me on which principle rockets work and how? --Sunny Singh 16:51, 22 July 2012 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)

See rocket. Looie496 (talk) 17:31, 22 July 2012 (UTC)

If that article doesn't answer all your questions, please ask us specific questions about the propellants, aerodynamics, guidance systems, etc. StuRat (talk) 19:05, 22 July 2012 (UTC)

Rocket flight *in vacuum* is often quoted as an example of Newton's third law, which is a consequence of conservation of momentum. Low mass propellant goes in one direction at high speed; more massive rocket goes in the opposite direction at lower speed. Gandalf61 (talk) 15:22, 23 July 2012 (UTC)

What do butterflies eat?

butterfly is herbivorous or carnivorous i like to know? — Preceding unsigned comment added by 1.187.13.34 (talk) 17:21, 22 July 2012 (UTC)

Herbivorous, if they eat at all. Looie496 (talk) 17:31, 22 July 2012 (UTC)

Most adult butterflies sip flower nectar, but other imbibe fluids from sap flowers on trees, rotting fruits, bird droppings, or animal dung. OsmanRF34 (talk) —Preceding undated comment added 17:52, 22 July 2012 (UTC)

They are not all exclusively herbivorous at all stages of their life cycle. For example, see Lycaenidae and particularly Miletinae. - Karenjc 19:08, 22 July 2012 (UTC)

Like Karenjc mentions, some lepidopterans are not herbivorous as larvae, some are predators, parasites, and scavengers. But these are very few in number - only about 200 species of lepidopterans are exclusively predatory or parasitic. Aside from the lycaenids, members of the families Epipyropidae and Cyclotornidae, for example, are unique among lepidopterans in that their larvae are parasites of other insects (primarily leafhoppers and cicadas).

In terms of adult lepidopterans, some species may feed (technically they drink) on carcasses of animals. This is an extension of a behavior known as mud-puddling, necessary for obtaining salts important for their metabolism that they do not receive from nectar (if they feed on nectar at all). This also explains why butterflies may sometimes land on humans (they're attracted to sweat). In extreme cases, some moths in the family Noctuidae, Pyralidae, Geometridae, Notodontidae, Thyatiridae, and Sphingidae actually drink tears (sometimes exclusively) of large animals including humans. They do this by either crawling over the edges of the eyes or hovering over the eyes with their probosces extended. Some species deliberately irritate the eyes by poking at it with their probosces or with their feet, a behavior that has been linked to keratoconjunctivitis in cows. In one species from Madagascar (which does not have many large animals), they instead drink the tears of sleeping birds by piercing the eyelids, and doing it in such a way as to not awaken them. And lastly, some members of the noctuid genus Calyptra are known as vampire moths because they drink the blood of animals (including humans) by piercing their skin. As far as I know though, no adult butterflies are actively blood or tear-drinkers.-- OBSIDIAN†SOUL 20:07, 22 July 2012 (UTC)

See calyptra (moth) (that other link points to a part of a plant). StuRat (talk) 21:57, 22 July 2012 (UTC)

Abovementioned corpse eating butterzombies: http://www.youtube.com/watch?v=ApWAs9P0Sh8 μηδείς (talk) 21:02, 22 July 2012 (UTC)

Objectum sexuality and orgasms without physical stimulation

let's at least sign this if we're going to address it further
The following discussion has been closed. Please do not modify it.
I was just reading this article, which is about on my level both intellectualy and puriently, and I was interested whether she actually is likely to have had a proper orgasm without stimulating herself at all physically (I assume for the moment that Ms. Liberty neither resisted nor reciprocated). An additional question incidentally - I hope none of us would class this as rape. Yet the only justification that I have heard for non-abusive bestiality being illegal is that the animals cannot consent. Well, neither did the statue here. Does that pretty much destory that justifaction? In fact I suppose one could be a bit more down to earth and compare two examples: a vibrator, or a dog licking up peanut butter strategically placed. Any sensible differentiation between the two? Actually tehre are so many questions here that it may be daft having it at the reference desk, but I will post it and see if anyone is interested. Otherwise, it's going to a message board! 21:39, 22 July 2012 (UTC) Personal opinion here: First, when you suggest that looking at a statue has the same legal implication as humans having sex with animals, I have to think you are verging on trolling. As for the vibrator and the dog comparison, to the best my knowledge, there has never been a Society for the Prevention of Cruelty to Inanimate Objects. That part is just silly. I'm not just talking about looking at it. I'm talking about have physical contact with it, which a lot of them do. And when I refer to sex with animals, I am not talking about all kinds of potential intercourse with animals (e.g. mr hands or worse) - I am talking particularly about the kind in which the animal is going about its business and so far as we can tell has no knowledge about it being a sexual activity (such as my peanut butter eample) Egg Centric 23:24, 22 July 2012 (UTC) Looking for cite; believed to be factual: Your first question is answerable: yes, both men and women can have orgasms with touching anything on their bodies at all. There is a whole website about it, though I didn't stop to read any of it. It is taught in seminars on sexual technique, and is sometimes used as a way to learn to control premature ejaculation in men. (I'm looking for a cite.) Bielle (talk) 22:10, 22 July 2012 (UTC) Yes. At the very least, I would remind the OP that animals are not things. [1] SemanticMantis (talk) 23:24, 22 July 2012 (UTC) Of course animals are not things. Not being funny, but I genuinely value my two dogs above 99% of individual human beings (which is not the same as saying I would kill 99% of humans to make them live - this isn't a trolley problem - it's more to do with me not having met 99% of humanity... actually I cannot see how anyone who feels different can have a pet as otherwise they would send the pet food money to charity). I think that Haidt has something to say about this, something about morality coming from personal relationships. Nevertheless, in a hypothetical situation where I were a bestialist (what is the correct term for that?) I would see no problem with the peanut butter situation I described. Well I accutally wouldn't because I wouldn't give my dogs peanut butter either but I'm being a bit silly here focussing on problems with scenarios... must repeat... DON'T FIGHT THE HYPOTHETICAL, EGG... Egg Centric 23:30, 22 July 2012 (UTC) Golly, I have a lot to learn to learn! Egg Centric 23:24, 22 July 2012 (UTC)

heat wave

Just thinking - Could the Japan Tsunami and resulting change in the tilt of the earth be a cause of the heat wave in the USA? — Preceding unsigned comment added by Bobant28 (talk • contribs) 21:47, 22 July 2012 (UTC)

Unlikely. The tilt of the Earth changed by a tiny amount, while the jet streams which drive weather patterns move by hundreds of miles. StuRat (talk) 21:50, 22 July 2012 (UTC)

[2] Count Iblis (talk) 03:29, 23 July 2012 (UTC)

Ah, Excellent, that clears it up. No arguing with that!!!!! Richard Avery (talk) 07:19, 23 July 2012 (UTC)

Indeed. Very illuminating... --Tango (talk) 11:44, 23 July 2012 (UTC)

Firstly, the change in the axial tilt was caused by the earthquake, not the tsumani. The tsumani was also caused by the earthquake. Secondly, as StuRat mentions, the change in the tilt was tiny ("between 10 cm (4 in) and 25 cm (10 in)" according to 2011 Tōhoku earthquake and tsunami). There is no way a change of a few centimetres coult have measurable climatic effects. Also, there is no reason to be looking for a cause of this heat wave. Heat waves happen. They've always happened and they will always happen. It's just part of normal weather. --Tango (talk) 11:44, 23 July 2012 (UTC)

Please may we have a share of your heatwave? So far this summer, we've had almost constant cloud cover and lots of rain where I live! Dbfirs 12:52, 23 July 2012 (UTC)

A share ? You're welcome to take it all. A/C running non-stop here in Detroit and not able to keep up. StuRat (talk) 21:25, 24 July 2012 (UTC)

Just a little bit of sunshine would be nice. I turned off my car heater for the first time today, but still have heating in the house. At least the drizzle stopped this afternoon, and the sun shone for about one minute! Dbfirs 21:34, 25 July 2012 (UTC)

You didn't send us much! Yesterday afternoon was warm and sunny. The temperature reached 72 degrees (that's 22 of those Celsius things for those who use them) but the rain started again this afternoon and it feels colder [only 58 degrees (14C)]. Still, this is England: we wouldn't have anything to complain about if we didn't have weather! Dbfirs 16:01, 28 July 2012 (UTC)

Added reference DOI not linking and same reference showing multiple times.

Hello,

I edited the pages on "polymerase chain reaction" and "Real-time polymerase chain reaction" to update them. When I added the reference, the DOI didn't come through as a link after the reference. Also, multiple instances of the reference are showing as different numbers in the reference list.

I know you get a million of noobs like me not doing something simple, but I can't find help in the archives. — Preceding unsigned comment added by Wine Weed (talk • contribs) 23:11, 22 July 2012 (UTC)

You wanted {{doi|... instead of {{doi:... per {{doi}}, and see WP:NAMEDREFS. 75.166.200.250 (talk) 01:47, 23 July 2012 (UTC)