Wikipedia:Reference desk/Archives/Science/2007 January 3

=January 3=

Freezing water: If there is no room for expansion, will it still freeze?
On Christmas day, I was putting some bottles of seltzer water outside to cool when this popped into my head. All of the chemistry teachers at my school could not come up with an answer:

If you freeze water, it expands. If you, say, freeze a bottle of water, the pressure gets to the point where the bottle bursts. Now, what if you filled a burst proof container with water and put it well below 0°C and standard pressure (1 atm). If there is no room for the freezing water to expand into, and the container cannot burst, expand, or bend in any way, does the water freeze?

I found articles online with almost identicle questions, but all the responses were along the lines of 'the container would end up breaking under those temperatures.' Just for clarity, let me state that it is a hypothetical, un-breakable container in an ideal universe. And depending on the response to this question, there could be a second part to it:

If the answer was that it would not freeze without room for expansion... then what would happen if the container suddenly opened up (i.e. if you took the lid off the bottle)? Would all the unfrozen water suddenly freeze into a solid?

Please help me out here, this has been bugging me for almost a month!

151.197.51.42 23:52, 2 January 2007 (UTC)Rob Cull


 * I'm not too sure, but if I were to guess I would think that it would expand until it hit the walls and then just become more dense and kind of expand into its self. Imaninjapiratetalk to me 00:04, 3 January 2007 (UTC)

So you're saying it could become a sort of... super dense solid? 151.197.51.42 00:06, 3 January 2007 (UTC)Rob Cull


 * Well now, I just read the article on water and it says that when it expands it is becoming less dense so I guess I was wrong. If I were to take another crack at it, I would say that it just would simply not expand if it can't break through the walls. The really smart people who have taken chemistry classes will answer your question sometime soon, so you will get a better answer than I can give. :-) Imaninjapiratetalk to me 00:12, 3 January 2007 (UTC)

It can freeze. As it does so the pressure will increase within the container. This will decrease the freezing point somewhat below 0 C, but you can continue to freeze it by lowering the temperature. Because of the large density change associated with ice, unless the volume involved is very small most any practical container will either expand or break before the water freezes solid, but it is not impossible to freeze water in a sealed container. Dragons flight 00:35, 3 January 2007 (UTC)


 * Your answer can be found here. If we were to put your sample of water in an infinitely strong container (such that no expansion was possible), you can follow the 0°C line upwards and see what happens. As any ice (Ice-I) forms and the pressure rises, the freezing point is depressed, preventing further freezing (and, presumably, limiting the pressure rise). But drive the temperature low enough and you'll eventually transit through a whole set of interesting phases of water ice.


 * And yes, you can easily see how pressure affects the freezing point if you've ever partially frozen water in a plastic bottle. The bottle isn't infinitely strong so it expands to accommodate some of the rise in pressure. But if you uncap the bottle, the pressure suddenly becomes ordinary atmospheric pressure and you'll often see more freezing take place; sometimes the entire contents freezes.


 * Atlant 00:39, 3 January 2007 (UTC)


 * Here's a way to think about this, though not necessarily school-level I'm afraid.
 * Work out the pressure assuming that it does freeze. Treat it as a two-step process, first imagine it freezing at constant pressure (with some volume change), then imagine compressing it back to the original volume.  The ice article gives densities of ice and water which imply a 9% volume change on freezing, and one source says that Young Modulus of ice is 9GPa ; together these give a pressure of 0.8GPa or about 8000 atmospheres.
 * Then ask whether it would actually still be solid at that pressure and temperature. You haven't stated the temperature, but certainly the higher pressure will tend to lower the melting point -- qualitatively by Le Chatelier's principle, and at Clausius-Clapeyron relation is a quantitative treatment of this exact problem, where it is calculated that the melting point drops by 1°C for every 13.1MPa pressure, so this would give a drop of 62°C at 800MPa.  Actually that's not quite true because the example is linearized about 0°C and this is a large enough temperature change to notice that the melting point versus pressure graph isn't a straight line.  But it's enough to give an idea that the melting point will drop considerably, and so assuming that you're envisaging temperatures just a few degrees below 0°C you would still have liquid water.  The actual pressure will still be raised, but not by as much as it would have been under the above assumption if it had actually frozen.
 * Hope that helps. &mdash; Alan✉ 00:52, 3 January 2007 (UTC)


 * So the final verdict is that the water will freeze, but only at a much lower temperature, because the pressure inversely affects the melting point? 151.197.51.42 01:10, 3 January 2007 (UTC)Rob


 * Not necessarily. Re the link posted above by User:Atlant, this page (linked from it) is of particular interest, and specifically the bit that says: "An interesting question concerns what would happen to water cooled below 0°C within a vessel that cannot change its volume (isochoric cooling)..."  I won't paste an extended quotation here because of copyright, but you'll see that it goes on to say that it won't freeze until at least -109°C and maybe never.  &mdash; Alan✉ 01:13, 3 January 2007 (UTC)

For this question, you need a phase diagram for water that extends to very high pressure regimes. Here's one. Note that instead of just having three regions like a basic phase diagram, this figure identifies about a dozen different phases. (Gas phase is beige, liquid is green, and solid phases are shades of blue.) Our article on ice also has a list of the known and described phases of ice, albeit without the figure: Ice. What we normally think of as water ice is ice Ih, a hexagonal crystal form of ice with a density of about 0.92 grams per cubic centimeter. (Liquid water has a density of about 1 g&middot;cm-3.)

Note that the phase diagram shows quite a few other solid ice phases. If you scroll a little past halfway down that linked page, you'll find a table of structural data that includes information about the densities of the different ices. Most of them only exist at obscenely high pressures, but you'll note that many of them have densities above that of liquid water.

We're now on the home stretch. We know that your bottle stays the same size, and we know that it contains the same mass of water throughout the experiment. Therefore, its density is going to stay fixed, at 1 g&middot;cm-3. Just above that table of structural data we were looking at is a map of pressure and temperature, coloured in by density. There's a medium-gray colour that corresponds to a density of 1.0. Most of the liquid water regime is about that colour, as the density of liquid water is fairly constant.

As you move to lower temperatures, the pressure associated with this density shoots upward, to somewhere a little bit above 108 Pa. The gray region also gets compressed to a narrow line; what this indicates is that it follows a phase change between two ice states. If you take this pressure to your phase diagram, you can figure out that you've got a mixture of ice III (or ice II at very low temperatures) and Ih. TenOfAllTrades(talk) 01:32, 3 January 2007 (UTC)

Addendum. Of course, in the simple case where you just drop the temperature a few degrees below zero Celsius in a fixed-volume container, you'll just depress the freezing point and get liquid water under pressure.

I have personally observed this phenomenon when attempting to rapidly chill a bottle of beer in the freezer. I left the beer in the freezer a little bit too long, but when I pulled the bottle out the beer was entirely liquid. The instant I removed the cap, two things occurred. First, the reduced pressure immediately allowed some of the beer to freeze. (Not all of it, as the process of forming ice crystals releases heat and brings the temperature back up to beer's freezing point). All the ice crystals floated to the top, of course, forming a beer slush in the neck of the bottle. Second, all those little tiny ice crystals provided convenient nucleation sites for bubble formation, generating a ton of foam and (tragically) spilling some of my ice-cold beer. TenOfAllTrades(talk) 14:27, 3 January 2007 (UTC)

Should use pure water, then it wouldn't freeze at all, even if the pressure drops. And you can't get a ton of foam, it's density is far too low.


 * Pressure does raise the freezing point of water (as well as the boiling point) but I'm not sure if you can prevent it from freezing altogether. This also requires a container that will not expand, trust me, frozen water in a glass bottle just makes a mess. Wintermut3

Hexane production in Nigeria
Please, is hexane produced in Nigeria? If it is, please comment on its production with a detailed flow diagram for hexane and if it is not, please give reasons why it cannot be produced there. Thank you.151.197.51.42 00:07, 3 January 2007 (UTC)Michelle
 * Were you hit by the 'I've got a stash of Hexane in Nigeria' letter? :) Advance fee fraud  --Zeizmic 00:53, 3 January 2007 (UTC)


 * I'm sure it can be done. If it's not produced there, it's because they lack the proper equipment to do so. - 131.211.210.17 08:39, 3 January 2007 (UTC)

Sister symptom to motion sickness
Motion sickness is caused by a discrepancy between the inner ear detecting motion and the eye perceiving none. What is it called when the inner ear detects no motion, but the eye perceives some. I get this when I play certain video games. --Brad Beattie (talk) 02:06, 3 January 2007 (UTC)


 * It's called simulator sickness.Vespine 03:07, 3 January 2007 (UTC)

Wahhhh. Physics is so confusing
I am studying oscillations in AP Physics C in highschool and am utterly confused. I've found two questions, however, that I think might settle some of the confusion, and I'd appreciate any help. These are not homework questions. One is sort of a part of one, but I just don't get the concept. At any rate. At the very beginning of the chapter, they give me the terrifically irritatingly complicated equation:


 * $$ x(t) = \Chi \cos(\omega t + \phi_0)$$

in which x(t) is displacement X is max displacement (amplitude), Omega is angular frequency, t is ???(time?), and phi is "initial phase." Very little attempt was made to explain what really any of this meant, and I am particularly confused by t (I don't know for sure what it stands for) and phi. What is god's name is the initial phase? They say it's also called the phase constant or phase angle, but I don't know what it means physically and how to use it in an actual problem. What are it's units? How does one get it from other variables? I think, from what I can tell, it means the original displacement, but then is it always zero? Is it never zero?

The other question is somewhat homework based, but I'm really confused and it's only part A of five parts. I'm coming back from break to a quiz and have no opportunity to ask my teacher about this. The question starts with a massless spring with a small object held at a position y1 (is this analogous to phi?) and then released. It oscillates to a max of 10 cm below y1. The question is what is the frequency of the oscillation. My only equations for frequency is $$\frac{\omega}{2\pi}$$ and that it is the inverse of Period (which is time based.) At no point in the question is time mentioned. How am I supposed to answer this? Thanks so much. I'm getting a headache from this and still making no progress. 70.108.219.115 03:59, 3 January 2007 (UTC)

oh, and what am i doing wrong with this math writing stuff? 70.108.219.115 04:09, 3 January 2007 (UTC)


 * For the 1st part, it's all to do with a sine graph. cos is really just sine shifted 90 degrees, if you look at the The f(x) = sin(x) and f(x) = cos(x) functions graphed on the cartesian plane. picture on that article. If you look at the animation there you can see a oscillation in progress. Your equation describes that type of oscillation. x(t) is the point which is drawing the line in that graph, X is amplitude, or 1 in this case, omega is 2pi, t is indeed time, the actuall passage of time as you are watching the animation, and phi is the initial phase, origin, shift, whatever you want to call it, in this case it is ZERO and generally if it is not specified, you can assume it is zero. As to what 'units' it is in depends on what units you are using, it is usually represented in fractions of pi or degrees. If that graph in the animation had been shifted to the right a bit, it would be greater then zero, remembering that sine and cos plus 180 degrees is the same as minus 180 degrees (2pi in the graph). Does this make any sense? I'll post this and try your second question. Vespine 05:04, 3 January 2007 (UTC)


 * (Edit conflict&mdash;this may be partially redundant with the above, but I figure another way of explaining can't hurt, and I already wrote it.) The equations look fine now, I think.  This is the basic equation for a one-dimensional harmonic oscillator.  t is definitely time, and almost always is in physics problems.  $$\omega$$ is the angular frequency, measured in radians per second; that is, $$1/\omega$$ is the time for the oscillator to change its phase by one radian.  Since the mathematical cosine function has a period of $$2 \pi$$, the equation repeats itself after the phase increases by 2&pi radians; thus the period is $$\frac{2\pi}{\omega}$$, so the frequency (not angular frequency, but rather the frequency for one full cycle) is $$\frac{\omega}{2\pi}$$, as you wrote.  The "initial phase" is just the starting place for the sine function; it it were 0, it would start out with its maximum value; if it were &pi;, it would start its minimum value; if &pi;/2, it would start at zero and decrease, etc.
 * I hope this helps! For more information, try clicking the articles I've linked in the above.  Another thing that might help you is to plot the function with different values of $$\omega$$ and the initial phase; that will give you a better understanding of how changing them affects how the oscillator evolves in time.  Please come back if you have more questions.  To other question-answerers: if I have any math mistakes in the above, please feel free to edit them.  Thanks! -- SCZenz 05:12, 3 January 2007 (UTC)


 * (after edit conflict) Accept our apologies for the equation being as complicated as it is, but if it was any easier, then it would probably not be the equation of an oscillation. In the equation the variable t stands for the time elapsed. It may (perhaps) help you to factor the equation into two parts:
 * x(t) = X cos φ(t), where
 * φ(t) = ωt + φ0.
 * The last line is the equation for the phase φ(t) as a function of the time t. It goes up linearly: if you plot the graph you get a straight line. Initially, when t = 0, you have for the phase φ(0) = φ0, which is why φ0 is called the initial phase. Because the phase is an angle and 2π is the angle of a full circle, two phases that differ by an integer multiple of 2π are equivalent: they give the same displacement. If they differ by an odd multiple of π, for instance 3π, they give displacements that have the same absolute magnitude but are opposite in sign.
 * So for example if ω = 10×2π/s (10 times 2π per second), t = 2.25s, and φ0 = π, then the phase φ(2.25s) = 10×2π/s × 2.25s + π = 46π, and x(2.25s) = X cos(46π) = X: the displacement at time t = 2.25s is at its maximum value.
 * There is a relation between the frequency of the oscillation and ω. The displacement goes up and down and up and down and so on; how long does it take to make one full swing? (This is what is called the period.) The time it takes for the phase to go up by 2π. In a time Δt the phase goes up by ωΔt; putting that equal to 2π gives us ωΔt = 2π, from which we find that the period Δt = 2π/ω. The frequency f is the inverse of Δt: f = 1/Δt = ω/(2π). For the example above, where ω = 10×2π/s, f = 10/s (10 times per second). I hope this gets you on track. If you have any further questions, please come back. --Lambiam Talk  05:25, 3 January 2007 (UTC)


 * As to the second question, I don't think there is enough information to work out the frequency. The amplitude is half of 10 cm, and the origin, or, the point of equilibrium of the mass before it was raised to y1 is y1 -5cm, but you do not know how fast it moved, or how long it took, it could be a really long spring and it could have taken seconds to get to y1 - 10cm, or it could be short spring at it may take a fraction of a second. I think there should be at least one more variable like the angular frequency. Vespine 05:53, 3 January 2007 (UTC)

Yeah. That's what I thought. And the book doesn't usually give trick questions, so...? I don't know. Thanks so much for all the help. That was quite helpful. There's something that happens to my head when I stare at all the technical jargon in my physics book, and I just can't understand it, no matter how often I read it over. You all clarified that a lot. Thanks, Sashafklein 06:13, 3 January 2007 (UTC)


 * For the second part, you can calculate the frequency of oscillation if you know the mass of the object and the spring constant of the spring - see Hooke's law and simple harmonic motion. Note that the frequency is independent of the amplitude of the oscillation (as long as the spring is not deformed so far that it ceases to behave linearly). Gandalf61 09:56, 3 January 2007 (UTC)

Homosexual High Pitched Voice
Is there a known biological reason for the fact that many gay men have high voices? Imaninjapiratetalk to me 04:49, 3 January 2007 (UTC)


 * There are many men who are heterosexual who are effeminate and often confused with gays. In many social settings and environments they are even regarded as gay to the point of embarrassment and redirection. 71.100.6.152 05:17, 3 January 2007 (UTC)


 * Less testosterone perhaps? --Proficient 05:18, 3 January 2007 (UTC)

I'm not sure it is a fact. See bear community; I don't think all those guys would have 'high voices'. Vranak 05:20, 3 January 2007 (UTC)


 * According to one researcher "Not all gay men sound gay, perhaps fewer than half" He notes that "only six studies that have tackled the linguistic patterns of homosexuals" and the stuff I could find was pretty obscure.   Nevertheless, biologically speaking, pitch is generated by the larynx and is modulated by testosterone (see here), so the question would be whether there are differences in testosterone between homo- and heterosexual men. There appears to be some dispute over this with some reports saying there is and some saying there is not. I'm not familiar enough with the literature to know if there is a consensus in the community. The alternative, of course, could be that gay men subconsciously adopt a higher pitch for unknown reasons. Apparently these chaps aim to investigate exactly that.  Rockpock  e  t  05:31, 3 January 2007 (UTC)


 * I'm convinced this is just a cultural thing. You may have noticed that gay man who sport a high voice also often use a somewhat soft and plaintive voice. Same thing. But you should not assume that men who speak that way are gay; it may just be how they naturally speak. --Lambiam Talk  05:36, 3 January 2007 (UTC)


 * Though if you did, you would be correct 62% of the time.  Rockpock  e  t  05:40, 3 January 2007 (UTC)

I know loads of gay guys who speak perfectly normally, but a little bit ago, I walked through one of New York's hip gay districts, and I couldn't here a single "normal" voice, only that stereotypically gay type. So my guess is that it's largely a cultural thing, and that people who are sort of embracing all the stupid stereotype crap that comes with being homosexual in this society (being good at fashion design, being a good sponge for "girltalk" etc) also embrace the stereotypical voice. It strikes me as kind of sad that anyone would make the conscious decision to do that and thereby further the extent to which his community is ostracized and classified. Sashafklein 06:11, 3 January 2007 (UTC)


 * Right, they should just behave normally, get a girlfriend and such, and everything will be hunkydory! --Lambiam Talk  07:32, 3 January 2007 (UTC)


 * That's not what he implied. --Wooty Woot? contribs 07:50, 3 January 2007 (UTC)


 * There is some, somewhat inconclusive, information in our articleGay lisp. --Lambiam Talk  07:47, 3 January 2007 (UTC)

I'd say it's a bit of both. That is, some homosexual men have different hormonal levels than heterosexual men, leading to higher pitched voices. This, incidentally, points to a genetic basis for homosexuality. Then, it became the "in" thing for gay men to lisp in some areas, while their lives would be in danger if they did so in other places. This resulted in  more lisping in "safe" areas and less in dangerous places. After all, a straight man can talk in a high-pitched voice and a straight woman can speak in a low-pitched voice, with a bit of work, showing that we have substantial control over our voices, if we choose to disguise them. StuRat 15:41, 3 January 2007 (UTC)


 * With respect, is that anything other than speculation? Rockpock  e  t  17:55, 3 January 2007 (UTC)


 * NO. There has been speculation for a century that testosterone deficiency in some form must play a role in development of male homosexuality, but no well-controlled studies have ever demonstrated a reproducible difference and few people knowledgeable about endocrinology and homosexuality think that future studies are likely to do so. alteripse 04:10, 4 January 2007 (UTC)


 * Exactly. For the record, there is no evidence that these hypothetical differences in hormone levels "point to a genetic basis for homosexuality". Nor is there any suggestion from experts that gay men consciously adopted a higher pitch or that it was ever considered an "in" thing in so-called "safe" areas compared to "dangerous" place. In studies that do find a significant difference in pitch, the authors only suggest it is subconscious and/or biological. Rockpock  e  t  10:16, 5 January 2007 (UTC)


 * Saying it's "subconscious and/or biological" isn't answering the question. If subconscious, what causes this subconscious behavior ?  If biological, and not based on hormones or genetics, what other biological difference is it based on ? And aren't there studies showing individuals related to homosexuals are more likely to be homosexual themselves, even if raised apart ?  This implies that a genetic factor is involved. StuRat 04:54, 6 January 2007 (UTC)


 * Obviously, at a most fundamental, reductionist level, everything biological and phsyiological has a "genetic basis". However, a tangental discussion on the genetic basis of homosexuality here is not relevent to the original question. The logical flaw with your point is this: there is no scientific consensus that gay men have a statistically significant difference in levels compared with straight men, therefore your conclusion is based on a fallacy. The fact is "horomone levels" are incredibly influenced by environmental factors (due to the complex feedback loops in the endocrine system). Thus - except in very extreme cases - they make extremely poor markers for genetic differences. So, irrespective of other strong arguments for some genetic influence in homosexuality, the literature shows differences in testosterone between adult males (which does influence voice pitch) is not a robust biomarker pointing towards that. You have every right to hold opinions contrary to the scientific consensus (or lack thereof), but this is not the place to express them. Rockpock  e  t  22:23, 6 January 2007 (UTC)


 * Saying "hormone levels are incredibly influenced by environmental factors", so can't possibly be related to genetic factors, is absurd. If we took an example of, say, the weather, it's also incredibly complex and influenced by many factors, but this doesn't mean that underlying forces, like El Niño, don't still have a measurable effect.  Also, your assumption that, if there is no current scientific consensus that something is true, then it can't possibly be true, is obviously false.  If this were the case, no scientific theory could ever be revised.  Also, anything which hasn't been studied would also fall into the category of "no scientific consensus exists", leading to absurd conclusions like "since nobody has studied whether eating oranges causes cancer, and therefore no scientific consensus exists either that it does or doesn't cause cancer, we must conclude that both statements are false".  StuRat 08:34, 8 January 2007 (UTC)


 * You are now misrepresenting my position (I never said "hormone levels...can't possibly be related to genetic factors", I was saying the research suggests they are a poor biomarker for genetic studies) and attempting to enagage in a completely tangental debate from the original point. This is not the place for challenging established consensus. The fact is this has been widely studied and - with all due respect - your contrary opinion is of no value whatsoever when compared with a body of literature. Your insistance in standing behind your theories with no basis in fact is not only damaging to your credibility, but to that of the entire reference desk. I just hope the OP was able to see your response for what it was. Rockpock  e  t  00:19, 9 January 2007 (UTC)

Aerogel filter
Can the various materials used to make Aerogel be adapted so that pore size is suitable for use in filtering out viruses and bacteria or specific gas molecules such as carbon monoxide? -- Adaptron 05:07, 3 January 2007 (UTC)


 * For a molecular sieve, you're better off using a zeolite. As far as I know, it's not possible to manufacture an aerogel with sufficiently narrow pore size tolerances to filter specific gases.  In any cases the typical minimum pore sizes (several tens of nanometers) are substantially larger than all but the largest molecules.
 * What you might be able to do is coat an aerogel with a catalyst or adsorbent. Carbon aerogels can have a surface area of up to 1000 square meters per gram of material, giving you a lot of area to interact over. TenOfAllTrades(talk) 14:08, 3 January 2007 (UTC)

There would be quite a bit of resistance to air by such a device, making it very slow at filtering the air. Adding significant air pressure to speed up the process would likely causes the aerogel to fracture. A traditional party balloon might be an example of a material that slowly filters air. They can take weeks to deflate, even with slightly higher air pressure inside. StuRat 15:26, 3 January 2007 (UTC)

Bicycle tire diameter...?
There are 63360 inches per mile. A 26 inch bicycle tire with a deformation diameter of 25.46479 inches caused by the weight of the bicycle and the rider will result in a deformation circumference of 80 inches which will cause the bicycle to travel exactly one mile in 792 revolutions. Was bicycle tire size designed to correspond to the distance of a mile or is this just coincidence? 71.100.6.152 06:51, 3 January 2007 (UTC)


 * Does compressing the diameter actually change the circumference or just redistribute it around the tread? If the tire rotates once, the whole tread-length has to go past the ground, even if it's not a perfect circle. Are you sure that "80 inches" isn't a rounding (sorry) error? If the goal is to get a specific answer (a pretty-looking number of revolutions) it's easy to back-calculate what the deformation diameter should be to get it:) DMacks 07:54, 3 January 2007 (UTC)


 * Consider that the part of the tire carrying the load is at a lesser diameter and is the true circumference following the road while the circumference of the outer tread is compressing and stretching and bulging inward to accommodate the relocation of support by the part of the tire closer to the rim. This budging inward accommodates its greater circumference. 71.100.6.152 08:44, 3 January 2007 (UTC)


 * I keep mine at a lower-pressured 25.21 inches, so that I do one mile in 800 revolutions. It's more work but easier on the tire-some arithmetic. --Lambiam Talk  07:55, 3 January 2007 (UTC)


 * I'd be pretty sure it's just coincidence. Even if all your figures and calculations are correct, e.g., your deformation diameter, there's a lot of assumptions. For example surely the deformation diameter will vary for riders of different weights or with different levels of tyre pressure (I also wondered about DMacks point, and Lambian suggests it does vary). Also 26 inch is not the only wheel size, and until recently at least it would not even have been the most common (if it indeed is now) - so why create the ratio based on this wheel size? And what is the significance of 792 revolutions anyway? I wouldn't mind guessing the deformation diameter is actually back-calculated off the even-figured circumference unless someone can provide some better information regarding where that figure came from. --jjron 08:14, 3 January 2007 (UTC)


 * Perhaps the words "approximate" and "mountain bike" would make a difference since hikers use footsteps to approximate distance traveled even though there is a great opportunity for variety between each. Even though I would actually prefer a smaller wheel diameter for riding through the woods and up and over obstacles and for distance measurement I could use either one it just seems curious that a 26 inch wheel has a convenient set of numbers to remember. 71.100.6.152 08:55, 3 January 2007 (UTC)
 * Convenient? Not at all, you have to remember conversion factors between inches, miles and sensible SI units! :) TERdON 13:37, 3 January 2007 (UTC)

Colonisation of the solar system
Make a wild prediction. By the year, say, 2100, how much of the solar system will we have colonised? Battle Ape 07:56, 3 January 2007 (UTC)
 * I wouldn't bet on anything beyond Moon and Mars. &mdash; Kieff 08:19, 3 January 2007 (UTC)
 * A wild prediction you say? I'd say the moon is a chance, and I wouldn't really call it colonised, I'd reckon perhaps a few space stations only at best with astronauts coming and going. The only other vague possibly in my opinion by 2100 would be Mars, but I'd think the chances of that highly unlikely. --jjron 08:20, 3 January 2007 (UTC)


 * Earth, and that's only if we're lucky. --Anon, January 3, 2007, 11:35 (UTC).


 * From my increasingly pessimisstic viewpoint, I think we'll be lucky to have permanent habitation/settlements of more than 10 people in orbit and on the moon by 2100AD. Mars might have visitors by then, who serve, say, 6 month-2 year stints maybe. I'm confident that Mars would be the limit of manned exploration though - unless something changes dramatically in our understanding of physics or we tame some new very energetic source of power.Robovski 04:25, 7 January 2007 (UTC)

2100 passed ages ago, it is 2760 in a few weeks. And by the 2100 you mean, we could be measuring years from a different year 1. It depends how much oil and valuable metals there are in space.


 * I'd agree with the Moon and maybe Mars, with one provision: I don't expect either to be a self-sustaining colony by that time. Both will likely need critical supplies from Earth, which makes them more like outposts than colonies, much like current stations in Antarctica.  Another possibility is artificial satellites.  The advantage of a planet or moon is a supply of building material.  Disadvantages include only having solar power half the time and having to deal with gravity during take-offs and landings.  Artificial gravity can be created on an artificial satellite by spinning it.  StuRat 15:14, 3 January 2007 (UTC)

avg. frictional force
What is the average frictional force when a man takes his usual 1km. walk? —Preceding unsigned comment added by 59.93.76.55 (talk • contribs)
 * I don't think that question can be answered. It's too vague. What kind of terrain, what's the weight of the person, what's the type of sole in his or her feet, and what area does it have? How do they walk? See: friction, weight, pressure &mdash; Kieff 12:14, 3 January 2007 (UTC)


 * ...and does the question want average over time or average over distance ? Does it want a vector average of the frictional force, or an average of the magnitude of the frictional force ? Exploring the many ways in which this question is ambiguous is quite educational in itself ! Gandalf61 12:19, 3 January 2007 (UTC)

Why is water removed from a washed hand when you shake your hands?...
After a good meal at a party you wash your hands and find that you have forgotten to bring your hand kerchief. You shake your hands vigorously to remove the water as much as you can. Why is water removed in this process? —Preceding unsigned comment added by 59.93.76.55 (talk • contribs)


 * Inertia and evaporation. &mdash; Kieff 12:15, 3 January 2007 (UTC)

The adhesion between the water and your hands is insufficient to withstand the forces applied to the water, so it slides off your hands, at least until the amount is reduced to the point where the adhesion exceeds the forces you can apply by shaking your hands. StuRat 15:08, 3 January 2007 (UTC)


 * Actually, it's internal cohesion between water molecules that you tend to overcome. I've never managed to dry my hands strictly by shaking: the layer of water directly adhering to my skin just doesn't come off. --Carnildo 00:37, 4 January 2007 (UTC)

circular motion
A bird while flying takes a left turn.Where does it get the centripetal force from? —Preceding unsigned comment added by 59.93.76.55 (talk • contribs)
 * By changing the angle of each of his wings, the bird can create an unbalance of forces on each of his sides. This unbalance of forces creates a "twisting" reaction giving the bird angular momentum. &mdash; Kieff 12:37, 3 January 2007 (UTC)
 * The bird is basically pushing against the air, it's basically a scaled down version of you swimming in water. Air seems like it has no mass to us because we are neither fast, light nor aerodynamic enough to really feel it, but to a bird, it's like swimming. If a bird tried the same trick in space, it would be able to turn its wings and body, but would continue flying straight because there would be nothing to push against. Vespine 22:07, 3 January 2007 (UTC)

tug of war
Can a tug of war be ever won on a frictionless surface? —Preceding unsigned comment added by 59.93.76.55 (talk • contribs)


 * Well, I can think of two ways of winning a tug of war on a frictionless surface. Hint: you are not told that the surface is horizontal and you are not told that it is flat. Gandalf61 12:27, 3 January 2007 (UTC)


 * I'm assuming that you don't have access to any kind of air-based propulsion (no jet engines, fans or blowing really hard)? La  ï  ka  12:49, 3 January 2007 (UTC)


 * Take off your shoes and throw them past your opponent as hard as you can. Dragons flight 12:56, 3 January 2007 (UTC)


 * Nice one. Just make sure you catch your opponent's shoes when they try the same trick. Gandalf61 13:48, 3 January 2007 (UTC)

Eat some beans and provide your own jet propulsion, being sure to turn around when you feel "inspired". :-) StuRat 15:04, 3 January 2007 (UTC)


 * Maybe you could use a gyroscope to rotate, and although you would end up with the rope wrapped around you, that might allow you to win. 80.169.64.22 19:17, 3 January 2007 (UTC)


 * How about leaning back and using the rope to upright yourself? --Bowlhover 22:47, 3 January 2007 (UTC)


 * That wouldn't work, your feet would slip forward, in a completely frictionless system. Vespine 23:55, 3 January 2007 (UTC)


 * jump.Hidden secret 7 21:26, 4 January 2007 (UTC)


 * In a totally frictionless system, any mass you eject will provide propulsion, so you could either choose to throw a few large masses reletively slowly, or a lot of small ones quickly. I'd carry a fully automatic BB-gun and get to shooting.  Either that or you could build a scaled down orion engine and detonate small explosives against a pusher-plate on your chest. Wintermut3 06:17, 6 January 2007 (UTC)


 * Sure, just be much heavier than your opponent. When you pull on the rope, your greater inertia will make you move toward the center much more slowly than him/her.  --TotoBaggins 15:17, 24 July 2007 (UTC)

acceleration due to gravity...
Suppose all of a sudden,the earth stops rotating...What will be the apparent value of 'acceleration due to gravity '?I mean - will it increase or decrease or remain same everywhere ;or will it increase/decrease at some places and remain same at other places...? —Preceding unsigned comment added by 59.93.76.55 (talk • contribs)


 * See Earth's gravity &mdash; Kieff 12:40, 3 January 2007 (UTC)
 * And Acceleration due to gravity too. Melchoir 23:08, 3 January 2007 (UTC)

It would increase slightly at the equator and remain unchanged at the poles. StuRat 15:00, 3 January 2007 (UTC)
 * I would me much more worried about the 'acceleration due to lack of rotation' since most of us are calmly spinning about the earth's center at a relative speed close to (or beyond) 1000MPH. The earth suddenly stopping without all of it's inhabitants stopping too would result in a rather cataclysmic disaster.  You know, just for speculation's sake.  --66.195.232.121 16:24, 3 January 2007 (UTC)


 * It would be interesting to consider what would happen if only the core stopped spinning; would the crust continue to slide around atop the magma but slow down, or is that not at all how the earth's crust works? grendel|khan 21:39, 3 January 2007 (UTC)
 * Wasn't there one of those god awful hollywood movies made about that exact scenario? I think it was even called The Core, yup there it is... Vespine 22:01, 4 January 2007 (UTC) -- Link corrected, Anonymous, Jan. 5, 01:22 (UTC)

Do inanimate objects 'know' they are being watched?
I am not mad, really. If I take two identical cups of boiling water, and sit and look at one of them for a few minutes it gets colder faster. I also tried this with identical plants, watching one and not the other, and the one I watched grew much fastr. Why would this happen?172.159.156.28 14:05, 3 January 2007 (UTC)
 * hey boy ...u try doin things bit scientifically .. try measuring their heights.. im sure u wd b gettin ur answer...

I did measure their hieghts, one is growing almost three times faster. Still not mad, 172.159.156.28 14:30, 3 January 2007 (UTC)


 * With two 'identical' cups of water, in the real world, you would expect some variation in the cooling recorded. That is, one would cool faster just because the world and equipment isn't perfect. So if you have two cups of boiling water, with a thermometer in each, you would expect one of them to cool faster. You would have been just as surprised to find the watched cup got cold slower as to find it got cold faster, but neither is unexpected. The same goes for the plant-growing. If you carried out this test hundreds of times with pairs of cups of boiling water, with the temperature being recorded by an automatic probe or a person who doesn't know which cup you're watching, and found consistent results, that would suggest you had an effect on it by watching. I suspect you would find the watched cup cooled slower about the same number of times it cooled faster. Skittle 14:34, 3 January 2007 (UTC)

Maybe this one really is mad. I also tried this on myself, and some of my fingers grew slightly when I watched them. Seriously, they did. 172.159.156.28 14:46, 3 January 2007 (UTC)


 * A person being near an object will increase it's temp due to thermal radiation from the person, and plants may grow more due to increased carbon dioxide exhaled from the person. StuRat 14:56, 3 January 2007 (UTC)
 * Curses, I was going to say that! Well, at least the second one. Melchoir 23:05, 3 January 2007 (UTC)


 * It's an interesting question on the nature of experiment - whether or not the observer affects the course of the experiment.. You might wan't to repose this question on the Humanties desk - someone with knowledge of philosophy might be able to give you a good answer.87.102.4.89 15:48, 3 January 2007 (UTC)


 * This is a case of confirmation bias. Hipocrite - &laquo; Talk &raquo; 15:57, 3 January 2007 (UTC)


 * I don't believe that you actually did the "experiment." Observing a plant with your eye and brain does not make it grow faster. I don't believe you actually sat down and stared at a plant for hours per day. Even if you did do something like this, you probably used low-precision instruments. X [' Mac Davis '] ( DESK | How's my driving? ) 16:06, 3 January 2007 (UTC)

This whole question seems like a joke, and too many people went along for the ride. -- Cyde Weys 16:09, 3 January 2007 (UTC)


 * Yeah, what about Schrödinger's cat? :) --V. Szabolcs 23:59, 3 January 2007 (UTC)


 * I must agree with Cyde Weys, as the question stands it has no answer, and deserves no reply, other than "do a scientific experiment, and ask when you have a description and data". --Seejyb 00:27, 4 January 2007 (UTC)


 * Seems a joke? He told us his FINGERS grew when he watched them... --Username132 (talk) 01:07, 4 January 2007 (UTC)
 * I think I did a nice job of not telling him he was an idiot! :) Ooops. X [' Mac Davis '] ( DESK | How's my driving? ) 04:06, 4 January 2007 (UTC)

This seems like a hoax, and not a very good one. Some made up data or a fake photo would make it better. Of all of them, I would say the last one is least impossible, as it could be related to hormones. Maybe if lots of people did the experiment...Hidden secret 7 21:35, 5 January 2007 (UTC)

step climber
hey friends.. plz help me im trying 2 make a step climber... to climb specifically sized steps and to come down without missing any of the steps.. i do have a idea to use a caterpiller type belt drive and the other with steps type wheel. which method should i prefer... if any other method ny ne could suggest ..help.. —The preceding unsigned comment was added by Sameerdubey.sbp (talk • contribs) 14:17, 3 January 2007 (UTC).


 * What advantages would that have to just running up and down steps ? It sounds like a needlessly expensive, energy-wasting, overly complex piece of machinery where none is needed, to me.  Sorry to rain on your parade. StuRat 14:53, 3 January 2007 (UTC)


 * I believe he is talking about a robotic solution to stair climbing. While it seems mundane to those of us with functional legs, those with disabilities see it much differently.  See Asimo for an example of innovation in this field. --66.195.232.121 16:18, 3 January 2007 (UTC)


 * I see, thanks for the clarification, I thought he meant an exercise machine something like a tiny escalator. StuRat 16:48, 3 January 2007 (UTC)

Further clarification is needed. Is this supposed to haul a person up and down steps or is it just a small device for a school project ? Can we assume the stairway is straight or would this need to handle spiral staircases, as well ? StuRat 16:52, 3 January 2007 (UTC)

ya.. im to participate in a national level robotics competetion and the problem statement is: " This event requires the participants to build a robot that can climb stairs of variable heights and also climb down. This robot will require the participants to put their elementary engineering knowledge of mechanics and electronics to practical use."

the heighest step in arena is 12cm and shortest one is 6 cms.


 * Are these stairs carpeted, plain wood, or what ? StuRat 21:34, 4 January 2007 (UTC)
 * please visit the following link: http://www.robotixiitkgp.org/events.php?page=sc

the steps detail and everything r given in link.steps are made up of rough wood

One design I can think of is a giant spiral which would roll up the stairs. I'd put sandpaper on the outside of the spiral to increase traction. To make the spiral small enough to meet the initial size requirements, it should coil up tightly. To drive the wheel you could use the contraction of the spiral as an energy source, with a weight at the center. I'm a bit worried about rule #2, though:

"The bot must go to all the steps. This means that it should completely land on the horizontal surface of each step."

If they mean it must put 100% of it's weight on each horizontal surface, then this design wouldn't work. Perhaps a clarification of that rule is needed ? Here's a diagram of my idea:

Before deployment:

+--+           |      |      +-+      +-+ @    |                  | -+                  +-

*** Mid-deployment:     *   * W * *            ************            *+--+       **** |      |     *+-+      +-+ **** |                  | -+                  +-

*     * After deployment:              *                 * *                       *            +--+       *            |      |      *      +-+      +-+*  W      |                  | ** -+                 +-

In any case, I suggest you create a full-scale model of the steps to be used in testing, whether you use my design or another. StuRat 04:25, 6 January 2007 (UTC)

the given idea is great..but dont you think it may become uncontrolled at times ..it may become a mockery in the arena.can you please clarify your idea.how to control it ..etc.


 * A fellow FIRST competitor? I used to be in the midwest regional of FIRST... anyway, do you have to step up the stairs? or can you simple build a long enough tread to glide up them with sufficient traction?  if you have to climb I'd suggest a two-stage drive system, one for flatland navigation and positioning on the steps, and then a pnumatic or electric-driven lift to rise you up to the level of the next stair in a stable way.  In my robotics experiance the simplest and most stable system usually wins out over the fancy one.  a tread drive is quite stable and has excellent traction, but less speed than wheels; I'd recommend a tread drive with lifting pnumatics. Wintermut3 06:22, 6 January 2007 (UTC)

Grover's Disease...Transient Acanthalytic Dermatosa
After more than two decades of suffering from this "transient" condition, would love to know if anyone has found a way to subdue, stifle, or (please oh please) cure it.


 * Consult a medical doctor? Splintercellguy 21:11, 3 January 2007 (UTC)


 * Try PubMed. Searching for "Grover's Disease", I see "Effective treatment of persistent Grover's disease with trichloroacetic acid peeling", "Grover's disease: successful treatment with acitretin and calcipotriol" and "Treatment of Grover's disease with tacalcitol" on the first page and a half of results. Of course, you should check with an actual doctor, but you might want to find copies of one or more of these articles and bring them with you. grendel|khan 21:12, 3 January 2007 (UTC)

Lemon Juice Causing Tooth Damage
Hello; Recently I've started flavoring my water and diet soda pop with Lemon Juice for enjoyment. My wife told me that using Lemon Juice would remove the enamal from my teeth. I called my dentist but was only able to speak with the appointment clerk. She told me that yes indeed LJ would remove the enamal. However she was very vague when questioned about safe, allowable amounts. I'm 66 years old and hope to live a normal life expectancy. I do enjoy the LJ but not at the expense of ruining my teeth. How, where can I obtain information regarding safe, allowable daily or weekly amount? Thank you very much. 16:03, 3 January 2007 (UTC)16:03, 3 January 2007 (UTC)Pane056
 * Adding lemon juice to your soft drink will not hurt your tooth enamel anymore than the drink does. If you munch on several lemons per day, continuously, that is what hurts your tooth enamel. Remember to always brush with a flouride salt toothpaste! X [' Mac Davis '] ( DESK | How's my driving? ) 16:08, 3 January 2007 (UTC)

Tooth enamal is not neccessarily a critically-limited resource; your body can generate more. Vranak 16:26, 3 January 2007 (UTC)


 * It's not so much the quantity of an acid that's the problem as the concentration. Lemon juice is a weak acid to begin with, and diluting it in the usual proportion with water or some other drink almost certainly makes the pH no longer acidic enough to cause damage, regardless of the quantity.  If, on the other hand, you keep a slice of lemon held against your teeth for hours each day, that might be enough to cause damage. StuRat 16:29, 3 January 2007 (UTC)


 * And it would be even worse if you kept replacing that slice of lemon with a fresh slice every five minutes. Vranak 18:47, 3 January 2007 (UTC)


 * Lemon juice has a pH of 2.2, well more than enough to attack enamel, which uncrystalises at 5.5. So it's all about the time and dose. Sadly, no one seems to have set a Recommended Daily Allowance for citric acid, although I may be wrong. La  ï  ka  19:15, 3 January 2007 (UTC)
 * Yeah but you are forgetting that the lemon juice is diluted probably at least 1:5 with water, if not less. If the water is relatively neutral, the result would be around 6, so I do not think diluted lemon juice is acidic enough to do any damage. Vespine 21:28, 3 January 2007 (UTC)


 * I would think that the acidity of the soft drink would be more of a concern than a couple of drops of lemon juice. BenC7 02:41, 4 January 2007 (UTC)


 * I would assume that hydroxyapatite in teeth is mostly resistant to weak organic acids, otherwise you'd have none left soon enough. I can't give concrete medical advice, your dentist can, but it takes the better part of three weeks for a high-molar phosphoric acid bath to dissolve a tooth, and low conc. citric acid is nowhere near that potent... it does depend on the state of your teeth and any potential conditions, but if the low conc. phosphoric acid and citric acid in soft drinks don't obliterate your teeth, less acidic flavored water with far less sugar should be safer. Wintermut3 06:25, 6 January 2007 (UTC)

Prime Gun or Primegun?
I am new to wiki and tried to define "Prime Gun" and "Primegun" as a new type of pellet gun. It was immediatly taken down as a spam. Would someone go to do some web research Google and you will find the site, and help me make this defintition. Primegun 17:30, 3 January 2007 (UTC) This is what I wrote

The "Prime Gun" was developed for people who would have a difficult time operating a traditional pellet or BB gun. A primer is loaded behind a pellet or Bb. A firing pin ignites the primer. The ignition force propels the pellet or Bb. The Prime Gun eliminates the need or cocking, pumping or gas containers. Source www.primegun.com

My apoligies if it was spam. please help Primegun 17:30, 3 January 2007 (UTC)
 * Usually when an editor creates an article with a username of the subject, and then leaves a link, it is usually considered advertising, as this is the tactic many spammers use. Please see WP:NOT and WP:N for notability guidelines. Has Prime Gun been mentioned in the press in any way? By gun magazines or television shows? Major gun websites (this is cutting it, but if you showed up with a 4 page review on the NRA site, for example, I think that would qualify). --Wooty Woot? contribs 21:06, 3 January 2007 (UTC)


 * I looked at Google (and your site). I'd say that your invention is currently non-notable; it's not being manufactured or sold to the public, the technology involved in it is not being used elsewhere at present, and it seems to have only two media mentions, both in the local (Des Moines) region; neither of which are available in the original formats. Caches of the Des Moines Register article reveal that it seems to be more of a "here's a local fellow with an interesting invention" nature rather than, say, a serious product review. So at this point, I'm afraid to say, I think your gun is non-notable. (If it makes you feel any better, I'm the (co-)playwright of a full length play that was well received when produced locally, won an award and got similar media coverage to your gun. But it's non-notable, and will remain so unless it receives professional production.) My rule of thumb is that if something I'm involved in is notable, I don't have to write the article about it; someone else will. --ByeByeBaby 01:16, 4 January 2007 (UTC)

Where does this saying come from?
(Paraphrasing) "It has never occurred that a theory prominent among experts has been overthrown by an untrained outsider spotting a simple logical fallacy." This was brought up at Hilbert's Grand Hotel paradox; I've also seen it mentioned when someone claims that the theory of evolution is a tautology. Does anyone know who said it first? grendel|khan 21:30, 3 January 2007 (UTC)


 * I don't think there's a specific saying or quote. It's just a quick and dirty way to say that any answer that seems to easy is probably not correct — a simple and fairly accurate heuristic but certainly not rigorous logic. --24.147.86.187 01:09, 4 January 2007 (UTC)


 * While we're at it, can anyone say who originally came up with the saying to the effect that "For every complex problem there is an answer which is simple, elegant, and wrong"? I have a vague feeling it might've been Paul Erdős, but that could be just a random misassociation.  —Ilmari Karonen (talk) 05:12, 4 January 2007 (UTC)
 * There is always an easy solution to every human problem—neat, plausible, and wrong.&mdash;H. L. Mencken, “The Divine Afflatus,” New York Evening Mail, November 16, 1917.&mdash;eric 05:47, 4 January 2007 (UTC)

continuous centrifuge or separator for getting water (and possibly foreign particules) out of oil
I have read the Wiki articles concerning centrifuges, centrifugation and also cream separators. I am trying to find if there exists a machine which would act as a continuous (rather than batch) process for separation. My application relates to cleaning used veg. oil in an effort to refine it to biodiesel. Current methods include pouring the oil through progressively finer screen or restaurant type filters (think big coffeemakers) to remove particulates and then heating the oil to boil off the water. The above filtering process is pretty labor intensive and the boiling is pretty energy intensive.

I'm just thinking there has got to be something which the oil can be pumped or poured through that can use the separating nature of a centrifuge on a continuous nature. That is to say, while only a pint of oil is being separated at a time, new (dirty) oil is being introduced, while "clean" oil continuously leaves the "machine".

I have also heard of using a bubbler to remove particulates. For this setup, all the oil is in one large tank with a layer of water purposefully in the bottom of the tank. An airstone is placed in the water layer. As the bubbles are formed and rise, they carry water with them through the oil, once the bubbles reach the top of the oil and pop the water droplets sink through the oil. The water molecules are attracted to the particulates and drag them down to the water layer. While this may help remove particulates from the oil, it adds water to the oil in the process. Any help much appreciated.Cmarcuson 22:14, 3 January 2007 (UTC)


 * Continuous-flow centrifuges are well-known. One can find them in apheresis machines, for example. But for this application, I'm not sure simple centrifugation will help...it only separates well if the things being separated have different densities and are not soluble in one another, which may not be the case for all impurities in your oil. OTOH, it's sometimes acceptible to add an easily-separated impurity if it helps remove a more difficult one, so adding water and then removing it along with (whatever particulates) could wind up being cheaper than designing some other way to remove the particles. Welcome to the world of engineering vs basic science. DMacks 22:20, 3 January 2007 (UTC)


 * If you look at the picture in our article Opposed piston engine, I think you'll find that the odd, silver-colored object at the end between the two engines is a centrifugal oil separator. And even if it's not ( :-) ), they were certainly widely used on diesel engines of that vintage. You can certainly find at least one on the USS Albacore (AGSS-569).


 * Atlant 01:59, 4 January 2007 (UTC)

Chlorate vs Chloride
What is the difference between the two in a scientific way. THe articles doesnt say. Dragonfire 734 22:45, 3 January 2007 (UTC)


 * The difference between chlorate and chloride? Check the articles again; the former has 3 oxygen atoms while the latter doesn't.  --Bowlhover 22:49, 3 January 2007 (UTC)


 * The suffix -ate indicates the presence of oxygen atoms, but not a specific number of them. It is the oxidation state which gives away (indirectly) the actual number of oxygen atoms. Only the chlorate(V) ion (ClO3-) has 3 oxygen atoms. There are four chlorates - I, III, V and VII. --G N Frykman 09:43, 4 January 2007 (UTC)


 * The above is pretty much spot on, but a helpful note -ide indicates an ionic compound with two elements (IE Sodium chloride, NaCl; Potassium Chloride, KCl; Ferric III Oxide, Fe2O3). Wintermut3 06:28, 6 January 2007 (UTC)

Polymeric material used in white goods
I would like to know what kind of polymers or composites are use in white goods, like refrigerators, vacuum cleaners, washing machines, dishwashers, toasters and irons? Thanks. 85.138.1.215 22:55, 3 January 2007 (UTC)Dias
 * Well, ABS would seem a very likely candidate for moulded exterior shells in eg. vacuum cleaners. Nylon, Polypropylene and Acetal resin are my best guess for non-metallic mechanical or plumbing  parts Malcolm Farmer 13:06, 4 January 2007 (UTC)