Wikipedia:Reference desk/Archives/Science/2008 March 1

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 1

Does anyone know the title of this painting about Galileo?

Dear Wikipedians:

Does anyone know what the title of the painting below is? It's supposed to be very famous, but I can't seem to find it anywhere on the net. It's about one of Galileo's experiments (I think).

Thanks.

L33th4x0r (talk) 00:48, 1 March 2008 (UTC)

See this page all about it. It's in Italian, but you should be able to get the gist. Apparently, the painting is part of a fresco in the Natural History Museum at Florence, by one Giuseppe Bezzuoli. --Milkbreath (talk) 01:04, 1 March 2008 (UTC)

Thanks so much! Now I know! 74.12.39.63 (talk) 01:51, 1 March 2008 (UTC)

I don't know enough Italian to easily understand the cites page, but I looked on it to see if I could tell what it said was the title. I thought Caduta dei gravi might be it, so I then did a Google search on that phrase restricted to pages that Google thinks are in English, looking for something easier to follow. Many of the pages were not really in English, but it only takes one good hit: this page gives the full title in Italian as L'esperienza della caduta dei gravi sul piano inclinato — which must mean "The Experiment on the Fall of Weights on an Inclined Plane". --Anonymous, 04:32 UTC, March 1, 2008.

Er, except that the one I found is not the same painting! It's small enough and dark enough that I didn't notice at first. It is very similar, though. I wonder if Bezzuoli painted the same scene more than once, or if one version might be a copy. Perhaps someone on the Humanities Desk would know something, or the Italian Wikipedia might have something if someone can read it well enough. --Anon, 04:40 UTC.

Thank you all for your help! I appreciate it! L33th4x0r (talk) 15:25, 1 March 2008 (UTC)

what is in Arizona sand?

We dug a bunch of sand out of a natural wash that runs behind our house in tucson Arizona to put in our childs sandbox. One of the children put a car in it that has magnets on it and it picks up tons of black magnetic material. What is this? —Preceding unsigned comment added by 71.215.107.211 (talk) 01:32, 1 March 2008 (UTC)

Lots of sand does that. We used to do it all the time when we were kids (in California, for me).

I did a google search for magnet sand black powder, and the second hit was this book, which says that the black powder is an iron oxide, Fe₃O₄, or magnetite. —Steve Summit (talk) 02:42, 1 March 2008 (UTC)

Another kind of black sand is ilmenite which contains iron and titanium. Graeme Bartlett (talk) 03:38, 2 March 2008 (UTC)

Persistence of hearing

Our house is pretty far away from the road, so we installed a wireless chime that rings inside the house when a car passes through the front gate. The chime is the familiar Big Ben ding-dong-ding-dong... pattern. Here's the odd thing: after it has rung, several different people hear ghost repetitions of the chime, sometimes over and over again, for quite a while -- it even stops for a while and then starts back up again. Kind of like an ear worm, but more ghostly. It's not a function of this house, either: we've got a guest house on the other side of the property, and there's a ringer there too, and the same persistence effect happens there. One more thing to add to the equation: the house is right on the river, at a noisy rapids, so there's always a significant amount of white noise in the background. My guess is that the white noise is cuing some sort of auditory memory or something like that. Has anyone ever seen anything of this sort in the literature? --jpgordon^∇∆∇∆ 03:13, 1 March 2008 (UTC)

Oliver Sacks explores the topic of "musical hallucination" in one of the chapters of Musicophilia: Tales of Music and the Brain. Your description sounds a lot like the way he describes it -- except that his description is not something applicable to every one. But in a mild form is fairly common, especially among older people, and definitely with some kind of noise source like a stream. I'm not sure it is the same as what you describe, but still you might find that chapter of his book interesting. Pfly (talk) 05:25, 1 March 2008 (UTC)

Maybe I'll get there; I adore Sack's work, but for some reason, Musicophilia isn't as compelling as his previous books. I bogged down, to my great surprise, since music and mind is one of my main interests. Thanks for the suggestion, though! --jpgordon^∇∆∇∆ 08:27, 1 March 2008 (UTC)

Just to say I get exactly the same thing from chimes, and did do even when I was young. Probably a very common phenonoma. I assumed it was something to do with those chimes being very clear notes - about which I intend to ask a question...87.102.79.228 (talk) 09:30, 1 March 2008 (UTC)

Furthermore, as I recall the ghost notes seem to be coming out of the noise ie I don't usually notice the noise - it's like a noise in my head/ears.. That is I think the chimes are causing me to hear noise after they have rung..87.102.79.228 (talk) 09:37, 1 March 2008 (UTC)

They might call in déjà entendu. I get it when I hear people talk about the "light at the end of the tunnel" in Iraq. Myles325a (talk) 23:30, 7 March 2008 (UTC)

SI Notation

I came across something unusual while reading a (very academic) paper: "Demonstration of the exponential decay law using beer froth" (Eur. J. Phys. 23:21-26). The author lists heights of beer foam in cm^-1, and the values start at 17 and end at 5. I am pretty sure this can't be 1/cm, since the values decrease with time, nor are they just cm, unless the beer glass is both very tall and filled with foam (possible, I suppose, but odd). Is cm^-1 a common notation for mm, or is this something more clever? Thanks, --TeaDrinker (talk) 05:12, 1 March 2008 (UTC)

Are you sure it was the foam height that the author gave? cm-1 = 1/cm, so it can be used when combined with another quantity, to express the magnitude of that quantity per cm. Ex. 23 J cm-1 = 23 J/cm --Bowlhover (talk) 06:32, 1 March 2008 (UTC)

I'm going to express the same concern/question here. There is no other way around it: Cm-1 = 1/cm and therefore over a given time period such a notation indicates an inverse. So if cm-1 decreases over time, the height is increasing. Can you link to the abstract? Wisdom89 _{(T / ^C)} 06:44, 1 March 2008 (UTC)

Google finds several links to the paper at for-pay sites plus this one link that doesn't work at the moment. However, they also have a cached copy converted to HTML. This is somewhat garbled but good enough to see that there really is a table with this peculiar $cm^{-1}$ usage in its column headings. Specifically, the first column is headed t(s), which must be time in seconds, and the second column is headed $h^{exp}cm^{-1}$. From context it seems clear that this means experimentally measured height in centimeters. (The third column shows the error in the height, and its heading also looks like $h^{exp}cm^{-1}$ to me; I assume a diacritical mark has gotten lost there.)

It occurs to me that if the height is 6 cm and you divide this value by cm, you get the pure number 6. So $h/cm$ or $h$ $cm^{-1}$ can be seen as a way of saying "height in centimeters". But I can't imagine why anyone would use this notation alongside the ordinary t(s) for "time in seconds". --Anon, 09:40 UTC, March 1, 2008.

I note that there is also a "-1" superscript on the best fit time constant line, τ_best(+/-RS)^-1. Clearly this is not measured in 1/s. My guess is the -1 is meant to refer to some kind of footnote rather than meant as an exponent. A more interesting question is why do the results only continue to 360 seconds? Did something happen to the beer after that short time? Another pertinent question: was the paper written on the same day as the experiment? SpinningSpark 12:10, 1 March 2008 (UTC)

There's a freely available PDF here. It is clear from this that Anon is correct. In Table 1, "$h^{exp}\ cm^{-1}$" is what we would normally write as "$h^{exp}/cm\$", meaning that the pure numbers in the table are measurements of the froth height in cm. In Figure 1 of the same paper, "$\tau /s\$" is used, so it's not as if the author is being consistent. The same goes for the best-fit time constant expression, which is actually "$\tau _{best}\ \pm \ \Delta \tau \ s^{-1}$", meaning that the numbers are measurements in seconds. "$cm^{-1}\$" and "$s^{-1}\$" in this context look to an English reader like a long-winded style of writing, but perhaps it is common practice in Germany, where the paper comes from. Any Germans reading this? --Heron (talk) 18:41, 1 March 2008 (UTC)

Thanks for all the replies! It sounds fairly reasonable that the measurements are in cm and the notation is expressing pure numbers, although (to my eye) unnecessarily complicated. Thanks again! --TeaDrinker (talk) 18:49, 1 March 2008 (UTC)

If you tabulate numbers without the unit, then the correct title of the column has to be divided by the unit (/cm) to make it mathematically correct. It then simply has the meaning "in cm". Сасусlе 13:51, 5 March 2008 (UTC)

door chimes

(also see question two above)

I've always though that door chimes gave very clear notes. Also any chime that is based on a hollow cylinder of metal (such as those wind chimes - when the winf blows a hammer to strike a cylinder)

I seems clearer than say a pure sine wave..

Can someone explain what quality of the note causes the clearness..

Also if you could relate the answer to the shape of the chime I would be interested. Thanks87.102.79.228 (talk) 09:34, 1 March 2008 (UTC)

The sound of a bell is fuller sounding than a sine wave because it is rich in harmonics. A traditional bell-shaped bell has a pronounced 13th harmonic (scientific notation = 12th overtone in music theory). This harmonic has a minor 3rd relationship with the fundamental and gives the bell its characteristic "minor key" sound. A tubular bell is also rich in harmonics, but does not have the pronounced 13th harmonic. To my ear they often have the bright sound of a "7th" chord, implying a strong 7th harmonic and clearly the lower ones are there as well. There have been attempts to cast traditional bells without a minor chord sound using computer calculations to predict the harmonic content of a particualr shape. Sorry, I do not have any references to hand but the shape of these bells differs from the traditional, firstly, in that there is a slight narrowing to a waist part way down and, secondly, there is no pronounced flare to the mouth of the bell. SpinningSpark 12:45, 1 March 2008 (UTC)

Ah, heres someone doing this [1] SpinningSpark 13:48, 1 March 2008 (UTC)

I wonder if the tubular bell lacks or has less 'inharmonic partials' as decribed in the links. When I here a bell shaped bell I often imagine I can here more than two notes competing. I'm guessing here (and I don't have the finest hearing) that the tubular bell might have less off these due to it being of constant width.

I'll have to try a 1st+7th harmonic next time I get near a frequency synthesiser and see if that sounds bright.87.102.83.246 (talk) 15:21, 1 March 2008 (UTC)

My guess would be that the simpler geometry of the tubular bell has far fewer modes of vibration, hence fewer opportunities for vibrations to develop out of harmonic relationships. Just mixing 1st + 7th sine waves will probably sound a bit odd, you will need some of the intervening harmonics also. SpinningSpark 16:39, 1 March 2008 (UTC)

Reflection

When a photon hits a mirror, exactly what happens, on a quantum level? In as plain language as possible, please. I'm just curious. Is it somehow absorbed and re-emitted, a la the Bohr atom (though it obviously can't be that if it is going to reflect), or something else?

Similarly, when people talk about an x-ray mirror, how does that work, on a physical level? Is it "true" reflection or is it something else? --98.217.18.109 (talk) 13:38, 1 March 2008 (UTC)

The photon is indeed absorbed and then re-emitted, although stricly speaking the reflected photon is not the same photon. The original is destroyed and a new one created. See this section of the Reflection article.

Regarding X-ray mirrors, these are no different in principle to regular mirrors. However, they are much more difficult to make because the wavelengths involved are much shorter than visible light. Hence the mirror surface needs to be orders of magnitude smoother. See [2] for NASAs' description of how they do it. SpinningSpark 17:59, 1 March 2008 (UTC)

The absorption and re-emission of the photon has to happen coherently - i. e. the intermediate quantum state is a mixture of different states where in each state another surface molecule has absorbed the photon. The direction of the reflected photon is then determined by constructive interference of these different states. Similar things must happen if a photon is refracted without being scattered. Icek (talk) 21:56, 1 March 2008 (UTC)

OK, those are both sort of what I wanted to know. I had imagined that it wasn't absorbed and re-emitted since I had been taught that the re-emission occurred in no particular direction at all. What is it about the properties of the atoms on the surface of the mirror that make them get re-emitted in the right direction? --98.217.18.109 (talk) 23:16, 1 March 2008 (UTC)

The special property is that the atoms have to be very close together so that emissions in the "wrong" directions are low probability because of destructive interferance of the wave states corresponding to emission by adjacent atoms. In other words, the surface must be smooth and shiny. A rough surface will have many atoms with no neighbours in a certain direction, emission in that direction is then possible because there is no other wave state to interfere. SpinningSpark 23:37, 1 March 2008 (UTC)

Thanks, that makes sense. --98.217.18.109 (talk) 03:04, 2 March 2008 (UTC)

Briefly following on to Spark's comment, the reflection in the right direction is the most likely, although there is a probability of some photons re-emitting in the "wrong" direction. This would correspond to what we typically call transmission (semi-transparent mirror). Every real mirror has some component of transmission and some component of reflection (and maybe some absorption as well); these numbers are typically provided if you purchase optical-grade scientific reflectors. Nimur (talk) 16:57, 2 March 2008 (UTC)

relativistic velocity masss ratio

If I have a particle of rest mass m₀ and I accelerate it to energy E, at which it is of a velocity comparable to c, so relativistic effects are clearly apparent, what proportion of the energy is velocity, and what preportion is converted to mass, via the mass energy equivalence? —Preceding unsigned comment added by 172.142.196.236 (talk) 13:56, 1 March 2008 (UTC)

All of the energy is mass because mass and energy are equivelant. They are the same thing, just different units and the conversion factor is C². However, this result from special relativity may help your understanding;

$E^{2}=E_{0}^{2}+(pC)^{2}$

where;
E is the total energy of the particle
E₀ is the energy at rest, ie the energy before you started acceleration the particle
p is the final momentum of the particle

In words E₀ is the component of energy due to the rest mass and pC is the component due to the motion. SpinningSpark 17:24, 1 March 2008 (UTC)

More than forty years ago, as a schoolboy, I recall reading a library book on Einstein and using the formula :$m={m_{0} \over {\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}\!$

to calculate how much the mass of an object increases with speed. I discovered that NASA wouldn’t create a disaster if they forgot about this effect in their calculations, because the difference in mass at escape velocity is too small to show on my calculator. Even at a hundred times escape velocity, the effective mass increases by only 0.0007%. To double the effective mass, you need to travel at 94.28% of the speed of light. At that time, I made the same mistake as some physicists early last century in believing that this increase in mass was “real”. In fact, it is just the kinetic energy converted to mass using Einstein’s equation $E=mc^{2}$. The situation is rather like driving round a sharp bend in a car. You feel what seems to be a “centrifugal force” pushing you outwards, but anyone standing outside the car knows that this is not a “real” force. You can treat it as “real” whilst you are in the car, and you get all the right answers, but once you take a more general view of the situation different equations are needed. In relativity, the idea of “relativistic mass” is rarely used because it only has meaning in the particular inertial frame of the observer. The true mass “rest mass” has not changed at all. The “extra mass” is simply the kinetic energy converted to mass. Mathematical physicists use a four-dimensional momentum vector to describe the situation. This includes the “rest mass” and the effects of the kinetic energy all in one vector which can be transformed to describe the situation for any observer. See Mass_in_special_relativity for full details. dbfirs 18:41, 1 March 2008 (UTC)

If your calculator is 40 years old as well, I would buy a new one. 94.28% C gives three times the effective mass. The correct answer for double mass is 86.6% C. In any case, the OP was not asking how significant the effect is at NASA velocities, he asked for the results at some unspecified velocity where the effect IS significant. Your example of centrifugal force in a car; all reference frames are equally valid (though not equally useful) according to General Relativity. This includes the frame referenced to the car, in which frame the force will be perfectly real. The idea that relativistic mass is an incorrect concept is highly controversial as is shown by the discussion on the special relativity talk page where I get the impression it is, in fact, a minority opinion. SpinningSpark 11:42, 2 March 2008 (UTC)

And even more controversial, it would seem, on the talk page of the article you referenced. SpinningSpark 11:57, 2 March 2008 (UTC)

Oops! No, not my calculator, my brain was at fault there. Sorry! (I set up a spreadsheet and used "Goal seek", then forgot what goal I was seeking.) My only excuse can be that I was distracted by losing internet access, hence the delay in my reply and not reading SpinningSpark's reply first. Also, I was not intending to imply that relativistic mass is a faulty concept, just that it is not the only way of looking at the situation. The idea that centrifugal force is an incorrect concept is also disputed, in fact it is a very useful tool to use in the frame of reference of the car, but many pedagogues insist that the force doesn't exist. It all depends on your point of view - it's all relative! dbfirs 08:01, 3 March 2008 (UTC)

Energy Question

If energy can neither be created nor can it be destroyed, why is it so important in our life or otherwise why is it so difficult to produce in plentiful amount? —Preceding unsigned comment added by 202.70.64.15 (talk) 14:38, 1 March 2008 (UTC)

I'm not quite sure what you're asking. If we simplify your question to why is energy so important in our life, the answer is obvious: it's important, we need it. It's not just important, it's vital: without food energy, we as organisms can't survive. And without various other forms of energy to manufacture and distribute our other creature comforts, our lives would be very, very different.

The fact that energy cannot be created just makes it all the more precious. —Steve Summit (talk) 16:37, 1 March 2008 (UTC)

There is for more energy around us than we could possibly use. The problem is: we can't use it. Although energy can't be destroyed, entropy can be created. One joule of heat is far less useful than one joule of electricity. — DanielLC 17:26, 1 March 2008 (UTC)

We want energy in a convenient form, such as chemical fuel (e.g. coal and petroleum), or stored electric potential (e.g. a electric battery). These forms are convenient for human machines and industries. Energy is also present in lots of inconvenient forms (e.g. waste heat; gravitational potential energy (such as the aggregate gravitational potential of all the matter which makes up our planet), but there is not an easy way to "plug in" to it. (See geothermal energy and hydroelectric power for some options). As you say, there is no "energy production", but rather energy "refining", which converts the form to something we can use. The previous answers have hinted at another core concept of thermodynamics, which is the entropy in our universe. To the best of our physical understanding, the universe started out with a certain level of entropy, and always operates to increase that level. When we cause energy to change forms, we are almost always increasing the entropy, which is an irreversible process. This sets hard theoretical upper-limits on the efficiency which we can perform energy-related tasks; but there are many other practical usability considerations to our energy needs which make energy "generation" difficult... for example, locating the petroleum, distributing the electricity, not generating harmful pollution in the process..., etc. Nimur (talk) 17:11, 2 March 2008 (UTC)

The principle behind diffusion

I think that I understand the process of diffusion. Gases or substances in solution move passively to areas of lower concentration down a concentration gradient, using molecular kinetic energy.

I do not, however, understand why this process works when applied to a system with lots of different substances. For example, during gas exchange in the lungs, why is there a gradient exclusively for oxygen and one exclusively for CO₂? Why does oxygen move into the blood simply because there is a low concentration there of oxygen? If there is a high concentration of gas in both the blood and the air space, why is there any net movement at all?

I hope I have made this clear. Thanks very much for your help!

86.146.107.210 (talk) 14:40, 1 March 2008 (UTC)

• It's not so much that molecules know to move to a lower concentration area. Think of the space in which the gases are contained as a glass of water. If you dissolve salt (let's imagine that is the gas) in that water, it will spread through all the water so there is a constant concentration. The same goes on in the lungs. There just happens to be a barrier in between. —Preceding unsigned comment added by 87.211.75.45 (talk) 15:43, 1 March 2008 (UTC)

Each individual gas molecule is moving independently and bouncing off of other molecules. After a period of time, you can compute the probability that that particular molecule will be in a given location, for example on one side or the other side of a membrane. So the underlying principle is not that you compute independently for each substance. Rather, you compute independently for each individual molecule. For example, If I have pure pxygen on each side ofthe membrane, there is no net movement, but individual molecules move back and forth across the membrane.-Arch dude (talk) 15:49, 1 March 2008 (UTC)

Actually in the case of oxygen, the blood binds the oxygen - effectively converting it to another form (that does not diffuse accross the membrane - too big) - so there should be a low concentration of oxygen(gas) in the blood. the complexing agent is Hemoglobin87.102.83.246 (talk) 15:58, 1 March 2008 (UTC)

The reason for diffusion is entropy. Entropy can be thought of as the degree of disorder in a system. A room in which the top 70% is nitrogen gas and the bottom 30% is oxygen is very ordered and thus entropically undesirable. A room where the two gasses are perfectly mixed is much more disorderd and thus entropically favoured. --Shniken1 (talk) 10:52, 2 March 2008 (UTC)

Every individual particle follows a uniquely random path - so the statistical aggregate of each particle is that everything diffuses, no matter what it is made of. As long as we can say that the inter-molecular forces are "negligible" (a good approximation for a lot of gas diffusion situations), each particle will diffuse just as if it were alone in an empty volume.

What would be surprising is when some unknown force causes two substances to stop diffusing - such as oil and vinegar. Something strange about those atoms appears (superficially) to defy the rules of thermodynamics! This usually involves strong formation of surface layers with unique alignment and chemical bonding, which prevents a normal diffusion process. In other words, we can no longer say that the molecules do not interact with each other.

The same thing can happen in an urban valley, when temperature inversion causes smog. If everything was diffusing normally, the pollution would mix thoroughly and dissipate, but instead it gets trapped, cannot diffuse, and becomes highly concentrated over the city. Nimur (talk) 17:18, 2 March 2008 (UTC)

Human evolution

what is the evolutionary explanation of sexual reproduction in animals? —Preceding unsigned comment added by 202.70.64.15 (talk) 15:04, 1 March 2008 (UTC)

That it is the mechanism by which individual species pass their genotypes to successive generations through their progency. Wisdom89 _{(T / ^C)} 15:05, 1 March 2008 (UTC)

Take a look at evolution of sex. It's a major topic of discussion and research. --98.217.18.109 (talk) 16:49, 1 March 2008 (UTC)

Subsidiary question - bisexual reproduction

All the postulated advantages of sexual reproduction in the article (rapid response to change etc) would equally apply to creatures reproducing bisexually (eg, the paramecium) since genetic material is being shared, but without the huge disadvantage of reduced productivity since both partners are reproducing. It strikes me that there must be something more than the genetic advantages at work here, for instance, the division of labour between the sexes might confer advantages. Is there any research in this area? SpinningSpark 18:33, 1 March 2008 (UTC)

The explanation I've seen for this (in Matt Ridley's The Red Queen, if memory serves), is that in an all-bisexual population, a male-only mutation would be at a significant advantage, since it would still be able to breed with (almost) everyone, and wouldn't have to waste all that energy on pregnancy, laying eggs, or whatever. Once the males were well established, there would be selective pressure to become female-only (to maximize breeding opportunities). I don't know if this idea is at all accepted. Algebraist 22:50, 1 March 2008 (UTC)

Reverse transcriptase PCR

I think I have the main idea of the technique clear in my mind, but I'd like a complete noob's guide to the technique. Does anyone know of any practical tips and protocols that are not covered in the article and its links that could help me out? --87.211.75.45 (talk) 15:37, 1 March 2008 (UTC)

Working in lab, I've come to realize that the best provider of molecular biology kits and protocols is probably Ambion. Try this link [3]. Wisdom89 _{(T / ^C)} 15:49, 1 March 2008 (UTC)

• Hmm, looks helpful, but why do they start about real-time PCR? - 87.211.75.45 (talk) 16:07, 1 March 2008 (UTC)

Real Time RT-PCR is becoming the standard for quantifying expression/mRNA levels - it's basically a way of normalizing each sample and allowing them to all be within the exponential phase of the PCR reaction with minimal operator intervention. Wisdom89 _{(T / ^C)} 20:39, 1 March 2008 (UTC)

composition of fecal matter

Is it true that most of the mass of human fecal matter consists of dead bacteria? --Halcatalyst (talk) 15:46, 1 March 2008 (UTC)

This paper [4] would seem to indicate that it is mostly water and fat. I would imagine that the majority of bacteria in the stool are still alive at the point of release. SpinningSpark 17:07, 1 March 2008 (UTC)

• However, the abstract (at least) says nothing about bacteria, or about total mass; it seems to discuss only nutrients. --Halcatalyst (talk) 21:47, 1 March 2008 (UTC)

I could be wrong, but my reading of the paper is that it is quoting figures in terms of the total mass (. . . results were expressed as concentrations (g/100 g of feces) . . .). Their result of 68.7 to 96.1 g/100 g of water does not leave much room for anything else at all to be the majority constituent. You are, of course, right that bacteria are not mentioned at all. SpinningSpark 23:52, 1 March 2008 (UTC)

• No, you're right; you read more carefully than I did. Thanks for the answer! --Halcatalyst (talk) 01:51, 2 March 2008 (UTC)

Some of that water is within the bacteria. The usual figures are for the percentage of the dry weight of the feces made up by bacteria. The specific figures vary widely according to techniques and assumptions as well as individual variation in diet, etc., and range from 10-42% of the dry weight made up of bacteria, mostly dead. So no, most is an overstatement; it would be more accurate to say that a considerable part of the mass of fecal matter consists of bacteria. - Nunh-huh 04:51, 2 March 2008 (UTC)

Dietary fiber makes up a significant portion of the dry mass. ike9898 (talk) 14:48, 3 March 2008 (UTC)

Parent/baby size

In honor of the 28" tall woman who recently gave birth to a normal-size baby, what species have the smallest and largest size ratio? Clarityfiend (talk) 17:27, 1 March 2008 (UTC)

As for smallest baby, my first guess would be a large marsupial, like the kangaroo. HYENASTE 17:46, 1 March 2008 (UTC)

Oh, gosh no, if it's not limited to mammals. --jpgordon^∇∆∇∆ 18:17, 1 March 2008 (UTC)

If we are going that way then bacteria have babies the same size as themselves, one at a time every 30secs..87.102.83.246 (talk) 18:37, 1 March 2008 (UTC)

More like 20 minutes, at the absolute minimum. Someguy1221 (talk) 04:20, 2 March 2008 (UTC)

Well, fungi spores can be microscopic and the fungus they grow into can be quite large. You said species, so I guess that counts too? — Kieff | Talk 05:05, 2 March 2008 (UTC)

Just as a reference frame, any organism that divides by mitosis produces daughter cells which are nearly identical in size - although, budding yeast produce daughter cells which are slightly smaller. Wisdom89 _{(T / ^C)} 05:44, 2 March 2008 (UTC)

Moon at past

bsm. Is it correct that the moon at least one time taked part (tow parts) and then joined? if that is correct, when and how many?(11-12) —Preceding unsigned comment added by 80.191.15.10 (talk) 19:09, 1 March 2008 (UTC)

That is not the currently most popular theory of the Moons formation. See Giant impact hypothesis. SpinningSpark 19:25, 1 March 2008 (UTC)

See Moon#Formation for a list of the ideas considered most likely. We have no way of knowing which is correct. It's still a subject of current research. —Keenan Pepper 19:37, 1 March 2008 (UTC)

Hot and cold areas

some of areas of earth are cool (mountains, highlands ) some of these are very hot (salty deserts (Kavirs or Sahras). At school, we study it ( or did) and all of us know it, but why? waht is relation between hight and temperature? —Preceding unsigned comment added by 80.191.15.10 (talk) 19:20, 1 March 2008 (UTC)

because you are away from the earth, which retains heat, and are high in the air, which does not retain heat. —Preceding unsigned comment added by 81.132.248.74 (talk) 20:47, 1 March 2008 (UTC)

The preceding answer is somewhat correct, but misleading. From this site: "Since air is "clear," sunlight passes through it easily and heats the ground. The atmosphere then gets heated from the ground and the atmosphere is warmer near the ground. As warm air rises from the ground, it expands and cools, and the sum result is colder air at higher altitudes than at the surface." Apparently written by a meteorologist. Tanthalas39 (talk) 23:44, 1 March 2008 (UTC)

80.191, please have a look at our articles on climate, weather, Earth's atmosphere and the like to gain some understanding. If you have additional questions, feel free to ask.

81.132: Having looked at you edit history from 01.03.08 I would suggest you acquire some maturity. --Cookatoo.ergo.ZooM (talk) 23:57, 1 March 2008 (UTC)

Remember that the thermosphere is HOT because it is in the Van Allen Belt. Hope this helps. Thanks. ~AH1^(TCU) 19:16, 2 March 2008 (UTC)

This phenomenon is due to two very simple things:

1. At higher altitude the air pressure is lower, because there is less air above pushing on it.
2. If air is compressed, it heats up (because we must do work on it to compress it), and if it expands it cools down.

With these things in mind, consider any well-stirred atmosphere. Any package of air that moves upwards expands and therefore cools down, and any package that moves downward is compressed and therefore heats up. The result is a thermal gradient, with temperature decreasing with height. (To be exact, this idealized situation creates an adiabatic temperature profile.) --mglg_(talk) 23:49, 4 March 2008 (UTC)

how long is a piece of string????

how long is a piece of string???? —Preceding unsigned comment added by 81.132.248.74 (talk) 20:46, 1 March 2008 (UTC)

3.2m. Your string may vary. Algebraist 22:44, 1 March 2008 (UTC)

See String theory for an answer to this knotty problem. --Cookatoo.ergo.ZooM (talk) 22:53, 1 March 2008 (UTC)

Double half its length.

1 - you may decide which answer you prefer. -mattbuck (Talk) 23:14, 1 March 2008 (UTC)

$\int _{P_{1}}^{P_{2}}{\sqrt {1+\left({\frac {dy}{dx}}\right)^{2}+\left({\frac {dz}{dx}}\right)^{2}}}\,dx$

where P₁ and P₂ are the ends of the string. SpinningSpark 23:28, 1 March 2008 (UTC)

As long a string as a string could string if a stringy string could string string. —Steve Summit (talk) 23:30, 1 March 2008 (UTC)

The answer is three, because "tri" is a piece of string. SpinningSpark 00:03, 2 March 2008 (UTC)

• Umm, take a peek at 81.132.248.74's other contributions.  :-( --hydnjo talk 00:30, 2 March 2008 (UTC)

Umm nevermind, it seems that I'm late to the party!  :-) --hydnjo talk 00:35, 2 March 2008 (UTC)

Besides, the answer lies without or within. ;-() --hydnjo talk 00:42, 2 March 2008 (UTC)

Unfortunately, that esteemed publication Do Ants Have Arseholes? and 101 other bloody ridiculous questions does not cover this one. But it does answer equivalent (if differently worded) questions such as "If a deaf man goes to court, is it still called a hearing?", "Where is the middle of nowhere?", "Is there another word for synonym?", and "Why do birds suddenly appear, every time you are near?". A must-read for all Ref Desk questioners and volunteers. -- JackofOz (talk) 01:00, 2 March 2008 (UTC)

I was about to ask where I could buy that alleged "esteemed publication", because I assumed you had pulled it out of your own... er, that you had made it up out of whole cloth. But no: ISBN 978-0-7515-4041-3. Whouda thunkit! —Steve Summit (talk) 16:50, 2 March 2008 (UTC)

Thanks for trusting me on this one, Steve. I was never more serious in my life. I re-read it often (it takes about an hour), and it has re-crystallised my whole attitude to this important facet of my life. -- JackofOz (talk) 00:58, 3 March 2008 (UTC)

The correct and simplest answer is, of course, the measured distance between the two ends when the string is stretched just taut —Preceding unsigned comment added by 79.68.188.203 (talk) 02:26, 2 March 2008 (UTC)

Which German architect do you mean by "taut"? :P I suppose you meant taut! (EhJJ)^TALK 03:13, 2 March 2008 (UTC)

The one who's always tight, of course! —Preceding unsigned comment added by 79.68.188.203 (talk) 04:56, 2 March 2008 (UTC)

char array[]="piece of string";

printf("length is=%d\n;",sizeof(array))

length is 16

-Arch dude (talk) 00:23, 3 March 2008 (UTC)

Casein Polymerisation Experiment

After innocently attempting the polymerisation of casein from warm cow's milk using an acid, I have produced some confusing results - can anyone shed some light on these, please?

If the suspension of fat in milk makes it translucent, why is the milk rendered colourless after the polymerisation?

Using full-fat milk (which gives the most polymer, suggesting it also has more protein) and malt vinegar, I produced a reasonable quantity of the polymer. This I split in half: one half was left to dry and the other was placed in the microwave for 45 seconds. The first sample became elastic and bouncy after one day and, after three, had formed a beige resin. This continues to shrink in size. The identical sample placed in the microwave came out of the microwave as a rubbery solid, which I moulded into a sphere and also left to dry - this was extremely bouncy within a few hours and then hardened, as with the other. The difference, though, was that the microwave polymer had gone red - both have now dried, and one is beige but the other is a very deep red. Why?

Also, I produced another normal sample (this time using red wine vinegar) but added sodium bicarbonate powder before it had dried. I kneaded this into the polymer for around five minutes. Gradually, it became like dough and formed a single mass, rather than many compacted strands. When this would absorb no more sodium bicarbonate, it was a dark, gristly grey, and is hardening only very slowly. The only reason for this that I can think of involves some reaction with the vinegar.

Thanks!

86.146.107.210 (talk) 22:56, 1 March 2008 (UTC)

If you are using full fat milk, your final result will include a lot of milk fat, and you may have produced cheese. Graeme Bartlett (talk) 03:47, 2 March 2008 (UTC)

FYI, polymerization isn't the correct term for what is happening to the casein in the situation you describe. You could call it curdling or denaturation and coagulation. ike9898 (talk) 01:08, 3 March 2008 (UTC)