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January 13

Conservation of energy?

when we push a wall and are unable to move it where does the energy goes —The preceding unsigned comment was added by 59.161.1.40 (talk)

Ceramic
your muscles heat up — Vranak

You are not expending any energy if there is no movement! Work = force x distance. So no distance --> no work. No work = no energy.

--Light current 00:19, 13 January 2007 (UTC)[reply]

You certainly are expending energy -- the energy just isn't doing work on the wall. As the previous poster said, your muscles heat up. --Anonymous, January 13, 00:44 (UTC).

Complete rubbish! —The preceding comment was added by Light current (talk • contribs) 01:15, January 13, 2007 (UTC).

So according to LC's theory, in climbing Mount Everest and returning you are not expending any energy, since the net distance = 0. And remember kids, no distance, no work! --Lambiam ^Talk 02:29, 13 January 2007 (UTC)[reply]

Pushing a wall is the same as leaning on the wall, same as sitting on a seat. No energy is expended. --Light current 02:48, 13 January 2007 (UTC)[reply]

Pushing a wall is not the same as leaning on it. Pushing is an active process that, assuming the wall does not move, produces an isometric contraction in muscles doing the pushing. At a microscopic level, crossbridges are cycling like mad to build up the tension to push the wall. Of course, you never build up the tension required to push the wall (hence it remains stationary), but the mere fact that you've begun pushing means that crossbridges are forming. Crossbridge cycling in skeletal muscle uses loads of energy in the form of ATP, so saying that pushing on a wall requires no energy is simply false. Care must be taken when attempting to interpret gross physical observations at the physiological level. The problem here is that you're assuming a human pushing a wall is equivalent to one point mass exerting a force against another more massive point mass. And that's just not the case. Cheers, David Iberri (talk) 03:08, 13 January 2007 (UTC)[reply]

Work is accomplished through small changes in position of cells in the muscle. This motion is converted to heat energy. It takes work and therefore energy to deform the cells of the muscle. --Tbeatty 03:00, 13 January 2007 (UTC)[reply]

If your muscles were not vibrating when exerting a force, there would be no heat produced. Energy is NOT expended by a force that does no work!--Light current 03:08, 13 January 2007 (UTC)[reply]

The person may not do work on the wall, but work is being done inside the person's body. A person pushing on a wall all day will certainly get tired; chemical energy is being used up. They would get hot & sweaty, etc. Anyway, I also think that perhaps (if you could imagine a wall made of something soft - say, rubber) that the space between molecules becomes compressed, albeit by a very small amount. So while it is being "pushed on", energy is stored in the wall. When the person lets go, the molecules pop back into their equilibrium position. All this would probably be negligible, however, compared to the energy converted to heat in the person's body. BenC7 03:20, 13 January 2007 (UTC)[reply]

As it happens, LC, I've addressed this precise question before. There doesn't have to be any macroscopic motion at all in order for work to be done: consider melting butter in a dish that is already exactly the right size to hold it. --Tardis 03:40, 13 January 2007 (UTC)[reply]

edcon

You say:

if you could imagine a wall made of something soft - say, rubber) that the space between molecules becomes compressed, albeit by a very small amount.

So in this case, movement is involved and (external) energy is indeed stored in the wall (just like you have stored a lot of potential energy by your body being at the top of everest) 8-)--Light current 03:44, 13 January 2007 (UTC)[reply]

All that energy storage in deforming the wall happens within a few milliseconds of you pushing on it — your muscles continue to become hot from doing work on themselves for however long you push. The latter effect quite dominates the former in total work done for any reasonable length of pushing. --Tardis 05:36, 13 January 2007 (UTC)[reply]

Well, clearly, everyone's right. Let's use a less ambiguous example than pushing on/leaning on a wall. A pillar supporting an object does no work on the object because the force it exerts on the object does not move along its line of action. A person holding the same object above their head does do work in order to keep their muscles extended. As a result, their muscles turn chemical energy into heat energy (remember, energy is not consumed, only transformed from one form into another). But still no work is done on the object - its energy is still unchanged. Beginners in physics/mehcanics are sometimes confused by this, and assume that a body that is doing work must be doing work on something, which is not always the case. Gandalf61 09:46, 13 January 2007 (UTC)[reply]

Gallium Reactions

Is there a list of materials that gallium combines with or corrodes?

Our article, gallium, mentions several gallium compounds including gallium arsenide, magnesium gallate, gallium citrate, and gallium nitrate. We also have a category, gallium compounds. - Nunh-huh 20:58, 12 January 2007 (UTC)[reply]

Chemical supplier?

What are good sources to order chemical supplies from? Suppliers similar to sigma aldrich, fisher sci, etc.

Uh, Sigma and Fisher would be good places to order chemicals from... So what is your question, precisely? Do you want a long list, or are you looking for the best (or any) source of a particular chemical, or a very high purity, or somebody that will sell to hobbyists, or what? --mglg_(talk) 21:29, 12 January 2007 (UTC)[reply]

And of course the answer might depend on what country you're in. --Anon, Jan. 13, 2007, 00:45 (UTC).

I am looking for a supplier that can give me the best price on a certain metal. I live in the US and have looked at Sigma and Aldrich but I wanted to shop around a little to see what other purities/prices others are offering.

Consider Wikipedia:Chemical sources --Mdwyer 06:40, 13 January 2007 (UTC)[reply]

Question 1 about my eyes

Two unrelated questions about my eyes: 1. Is there anything I can do to make the white part whiter?

It's best to keep unrelated questions separate, so I'm taking the liberty of splitting this item into two. --Anonymous, January 13, 00:52 (UTC).

If you think your sclera is unusually colored, then please, go to an opthamologist and let them answer your questions. — Kieff 03:20, 13 January 2007 (UTC)[reply]

Digital photo editing is how eye whitening is done. :) Otherwise, the only way I know of the change the color of your sclera is strictly related to the blood vessels. That is, vasoconstrictors (Visine) make the vessels shrink, and so the redness of your eyes is lessened. The effects are only temporary, and if you have concerns, you should really contact your eye doc. --Mdwyer 06:32, 13 January 2007 (UTC)[reply]

Sleeping well might help too Nil Einne 14:14, 13 January 2007 (UTC)[reply]

Question 2 about my eyes

2. How does squinting help me read a little farther when I don't wear my glasses?

Light rays from any particular point on the thing you're looking at spread out in all directions. When you see clearly, it's because rays from the same point that spread out and hit different parts of the pupil of your eye are properly focused by the lens of the eye to hit the same point on the retina.

If you need glasses, it's because the lens is not able to adjust to the right shape to achieve this focus. Then the rays from the same point hitting different points on the pupil will spread out to hit different points making a circle on the retina (the circle of confusion). If you look at a small bright light without your glasses and it's at a distance that you can't focus on, you will see that it spreads out into a circle.

When you squint, this obstructs part of the pupil, so the rays that get through to the retina are starting from a smaller part of the pupil. This reduces the circle of confusion. If the focusing defect wasn't too bad to start with, this may be enough to help you pick out the sharp edges you need to read. Incidentally, you may also notice that in bright light you can read without glasses better than in dimmer light even though you can still see to get around. This is for the same reason: your pupil shrinks in the bright light and again the circle of confusion is reduced.

--Anonymous, January 13, 2007, 00:55 (UTC).

You might want to research the pin-hole camera to see more about that whole circle of confusion thing. It is really pretty neat! The other reason squinting might help is because the force against your eye changes the shape of it. By changing the shape, you change the focus, and for a bare few seconds, you can see better. This is often why the first sign of eye trouble in children is rubbing their eyes in school. --Mdwyer 06:38, 13 January 2007 (UTC)[reply]

See also pinhole glasses. (There was also a classic Far Side cartoon featuring "early microbiologists" squinting through their fingers (in lieu of microscopes) at their primitive stone petri dishes, but I can't seem to find a copy on the web to link to.) —Steve Summit (talk) 14:48, 13 January 2007 (UTC)[reply]

Also, if you have astigmatism, squinting may deform the lens in your eye slightly in a way that corrects the distortion, which would improve your ability to focus. Maelin (Talk | Contribs) 12:40, 18 January 2007 (UTC)[reply]

Frog in boiling water

I first read about the analogy of the frog in boiling water in the book The Story of B, then I saw the analogy again in the film An Inconvenient Truth. The analogy is that if the frog is placed in a pot of boiling water, it will jump right out. However, if the frog is placed into a pot of room-temperature water, and the water is slowly increased to its boiling point, the frog will boil to death. The environmental plight of humanity has been compared to this. What is the origin of this analogy? If this does not apply to science, please move wherever necessary. —Erik (talk • contrib) - 02:45, 13 January 2007 (UTC)[reply]

According to Frogs in popular culture, it came from the book: "Life and Death in the Executive Fast Lane" by Manfred Kets de Vries. It is a myth, as stated in that article. My guess is that they completely made it up. If I put my frogs in cold water, they tend to jump out straight away. --liquidGhoul 03:05, 13 January 2007 (UTC)[reply]

The book you mentioned was published in 1995, but The Story of B was published shortly after in 1996. Is it possible that the comparison (however false, apparently) originated from something earlier? —Erik (talk • contrib) - 03:08, 13 January 2007 (UTC)[reply]

I can't find any more info on it. It is mostly used to explain to lay-persons about environmentalism. So there is a good chance that it is a recent story. However, I don't really know. If we can find an earlier book about it, I may look it up more. Thanks. --liquidGhoul 03:21, 13 January 2007 (UTC)[reply]

As spoken folklore it dates back much farther than that, as I have been aware of the analogy for maybe 3 decades. I doubt it is based on fact, but it certainly a picturesque and useful analogy. alteripse 04:17, 13 January 2007 (UTC)[reply]

Per the above, it is apparently untrue. BTW, anyone else remember any other recent TV shows (movies or whatever) where the frog analogy occured? I seem to remember hearing it (possibly reading it). But it wasn't either of the above since I haven't see or read either of them (it could have been from a trailer but I doubt it) Nil Einne 14:12, 13 January 2007 (UTC)[reply]

I can't see how it's a useful analogy when it's false to begin with. I suppose it's useful if your intent is to mislead. Vranak

What would be a more appropriate and accurate analogy to reflect that people tend not to react to slow changes as potently as quick changes? —Erik (talk • contrib) - 17:13, 13 January 2007 (UTC)[reply]

I've found at least one reference to it dating from 1990 (via JSTOR), so it must be earlier than both of those. Crispin Tickell, "Human Effects of Climate Change: Excerpts from a Lecture Given to the Society on 26 March 1990", The Geographical Journal, Vol. 156, No. 3. (Nov., 1990), pp. 325-329, on 325. --24.147.86.187 18:07, 13 January 2007 (UTC)[reply]

Hey — we have a boiling frog article. Whoa. --24.147.86.187 18:11, 13 January 2007 (UTC)[reply]

Via Lexis Nexis, I found a reference dating from 1980 from an article about survivalists who use the analogy to describe how they think society is going to collapse. Cammille Recchia, "Area Survivalists Circle Wagons for Coming Armageddon; Survivalists Prepare to Ride Out Armageddon; Fearing Economic Chaos, Advocates Store Food, Buy Gold, Silver", Washington Post (25 August 1980): C1. I'll keep poking around... (Can you tell that I do historical research for a living?) --24.147.86.187 18:16, 13 January 2007 (UTC)[reply]

OK, wow, I got a reference back to at least 1960. It's pretty humorous. It is an article about a certain J. Hannibal Rustbugle (who is likely fictional) who has gone into a reporter's office and demonstrate said frog experiment. "Behold the moral. The frog dropped into boiling water water has sense to leap out, but the frog dropped into cold water can be cooked to death before he realizes he is in serious trouble. So it is with us Americans and our civilization in this mounting crisis. We must beware of those who want to thaw the cold war out at any cost. We may be cooked before we realize what has happened. Every day in every way, enemies, dupes, and some well intentioned persons are busily stoking fires under the water. They are seeking to boil our freedom into nothingness. They can only be stopped if we keep a close eye on the situation." From Walter Trohan, "Report from Washington," Chicago Tribune (6 June 1960): 2. I doubt this is the first instance of its being committed to print, though it is the earliest I was able to find with all of my electronic databases. --24.147.86.187 18:26, 13 January 2007 (UTC)[reply]

Wow, that's incredible. Very interesting to know. Thanks for doing the research! —Erik (talk • contrib) - 18:28, 13 January 2007 (UTC)[reply]

A previous query seems to trace it back to at least 1952. My uninformed guess is that this became part of some sort of campaign speech that some candidate or another gave and made the rounds that way, but I don't know. I haven't found any earlier references. I would not be entirely surprised if it went back to the late 19th century, when researches into things like the physiology of boiling frogs was all the rage (I exaggerate, but only a bit), though as of yet I see no evidence. --24.147.86.187 18:45, 13 January 2007 (UTC)[reply]

I updated the boiling frog article with those references and a few choice quotes. A nice way to spend 20 minutes on a Saturday afternoon! --24.147.86.187 18:58, 13 January 2007 (UTC)[reply]

It is very old indeed! I have found a reference to it dating from 1893... will keep looking... --24.147.86.187 19:14, 13 January 2007 (UTC)[reply]

OK — here is the earliest I could find, and now I give up and continue my day:

By very gradual increase or decrease of temperature, a frog may be boiled or frozen to death without making the smallest movement.

From Harald Höffding Outlines of Psychology, Mary E. Lowndes, trans. (New York: Macmillan and Co., 1892), on p. 108. The entire paragraph (about temperature sensation) references some books in German from the 1860s, which I do not at the moment have at my disposal to check (nor is my German really up to par for it). It is available through Google Books. --24.147.86.187 19:23, 13 January 2007 (UTC)[reply]

Again, thank you very much for the research. Your answer was more than enough. Cheers! —Erik (talk • contrib) - 19:44, 13 January 2007 (UTC)[reply]

This is "science" from the era of Aristotle, who did "thought experiments" but did not bother to test the theories empirically. Having raised frogs, I claim that when the temperature becomes uncomfortable, they move. I have not attempted to boil frogs, however. If i did, I expect they would taste like chicken. Edison 23:19, 13 January 2007 (UTC)[reply]

I had a feeling before I read the popular culture arrticle (which obviously needs to be updated), that it would come from Asitotle's (I would have said Socrates') time. I thought this was a dead disucussion, and came back to it being huge! Great work everyone. --liquidGhoul 11:18, 14 January 2007 (UTC)[reply]

I did not mean Aristotle published this, just that it smacked of thought experiments from the era before empirical science. Edison 18:09, 15 January 2007 (UTC)[reply]

Galileo did thought experiments that he didn't test. Einstein did thought experiments that he didn't test. Doing thought experiments is not what distinguishes one from doing good science or not. In any case it seems to have its origins in early physiology work, as I suspected. As to whether it would work or not, I imagine it would depend a lot on the conditions — obviously just dropped frogs into buckets is not going to work, but you could imagine finding other ways to tell their reaction to temperatures. --24.147.86.187 17:26, 14 January 2007 (UTC)[reply]

There is a similar effect I've observed myself, you can close a pair of pliers slowly on a wasp. Quick movements will scare them off, but not slow movements. Don't try this at home ! StuRat 05:20, 15 January 2007 (UTC)[reply]

Then there's Don't Crush That Dwarf, Hand Me the Pliers. Edison 18:07, 15 January 2007 (UTC)[reply]

DVD Vs Real Life clarity

Question - Would watching a good quality DVD movie be clearer in seeing things around us in real life? If you understand what i'm talking about. I was just wondering because when you look around a room or something you have a small intereference of colour or patterns from looking at something bright to looking at something darker but we're so used to it that we don't really notice it, but it's still there. But if you look at a T.V. screen you don't get that interference. So does that mean watching something clear like a DVD would appear clearer than just looking around in real life? It's a hard question to explain, but I hope most people understand what i'm getting at.

No, it wouldn't be clearer, although it might seem that way if you were looking at a DVD of something magnified larger than it is in real life, or if the lighting was better than it was in real life. BenC7 06:04, 13 January 2007 (UTC)[reply]

Not if you attempt to reproduce the normal image on DVD. There is, however, some processing that can be shown on DVD that you can't see directly. An obvious case would be including IR and/or UV wavelengths shifted into visible colors. The contrast and brightness can also be manipulated to avoid blinding you (most monitors couldn't do that anyway), and to avoid having anything too dim to see. StuRat 05:11, 15 January 2007 (UTC)[reply]

Human vision also has a resolution of 15 variable-sized megapixels, where a DVD has a maximum resolution of about 377,000 pixels for brightness, and only 188,000 for color.--72.202.150.92 14:42, 15 January 2007 (UTC)[reply]

In any case you are still looking at the DVD with human vision, so any defects in human vision would be simply added to the degraded quality of the DVD. If DVDs look clearer to you, it is probably an illusion. --24.147.86.187 15:23, 17 January 2007 (UTC)[reply]

Ampules

Why are ampules still used for some pharmaceuticals? They are very inconvenient - the drug has to be filtered before use, and sometimes they don't crack open the way they are supposed to. The vast majority of drugs use a vial with a rubber stopper, which is convenient for single or multi-use. --Joelmills 04:49, 13 January 2007 (UTC)[reply]

Just a guess, but I assume it is because they can be heat-sterilized using hotter temperatures than rubber stoppers. They're also probably cheaper to manufacture. --Mdwyer 06:28, 13 January 2007 (UTC)[reply]

Another reason is to protect individuals who have latex allergies: [1]. Glass is also less permeable that virtually any conceivable stopper material; this can extend shelf life of drugs and protect them from spoilage due to premature exposure to air. Finally, a glass ampoule is about as tamper-resistant as packaging can get. You can't add something to an ampoule without breaking it open, and you can't reseal it. TenOfAllTrades(talk) 16:00, 13 January 2007 (UTC)[reply]

Also, some substances are not stable on air over a longer time so are shipped in ampules containing inert gases like nitrogen. -- 85.179.8.121 18:49, 13 January 2007 (UTC)[reply]

Thanks for all the responses. I will refer my annoyed technicians to this page. --Joelmills 22:21, 13 January 2007 (UTC)[reply]

Astronomical Distance

This must be an exceptionally easy question for somebody here: how is the distance and age of stars calculated? I understand the red shift can measure the speed at which a star is moving away (speed of universe's expansion) but can it also be used to measure the stars distance from us? I thought maybe it was measured using parallax, but apparently the interstellar distances involved are so huge that this doesn't work. -Kelly

There is no single answer. See the article Cosmic distance ladder for information on various techniques (including both redshift and parallax) used to determine distances to various stars. A very common method is to identify a particular star as being of a certain class, knowing that such stars vary in brightness between two figures, comparing that known range to the observed brightness, and then computing a distance which would cause such a variation in brightness assuming various factors in the intervening space. While often giving a fairly accurate range this also sometimes produces incorrect results when the observed 'star' turns out to be two stars in close visual proximity, if there are higher intervening concentrations of interstellar dust than assumed, or due to other factors. Most of the methods of measuring stellar distances involve such uncertainties and it is only through cross-checking via different methodologies that accurate values may eventually be determined. --CBD 13:00, 13 January 2007 (UTC)[reply]

Parallax is the primary method for determining stellar distances - they are not too far away, the cosmic distance ladder is used to measure the distances to galaxies. Redshift is not used to determine distances to stars because they are not caught up in the expansion of the Universe.

For determining the distance to galaxies, see Hubble's law.

Age is estimated by spectroscopy. Basically, the intensity of the star's light is measured for each wavelength, and at some wavelengths the light will be much more (or less) intense than at the surrounding wavelengths. These peaks and troughs are spectral lines and they indicate the presence of different elements. Older stars have more metals, which are elements heavier than helium. --Bowlhover 21:28, 13 January 2007 (UTC)[reply]

Resistance

—carry out investigation of the relationship between lenght of a metallic conductor e.g nichrome wire and its resistance — Preceding unsigned comment added by 89.101.116.77 (talk)

Okay - I've done it - can I have a prize now? :P

Seriously - this sounds like a homework assignment - you really should work out what you are going to do yourself. If you have any specific questions then feel free to ask them here. --Neo 13:08, 13 January 2007 (UTC)[reply]

*nudge nudge* Electrical resistance *hint hint* -O bli (Talk)^? 13:13, 13 January 2007 (UTC)[reply]

O.K., I finished the investigation. The longer it is, the greater the resistance, in direct proportion. Next homework question? Edison 23:22, 13 January 2007 (UTC)[reply]

Some of our posters are so resistant to doing their own homework that the longer we insist, the less we get through and the more heated the discussion becomes (depending on the material, of course). StuRat 04:56, 15 January 2007 (UTC)[reply]

Planet82

Does anyone know how this SMPD (Single Carrier Modulation Photo Detector) sensor that everyone's talking about works? The planet82 FAQ [2] looks to me more like a collection of buzzwords like nanotech, quantum tech etc rather then containing much useful info. I admit I've only done very brief searches so feel free to ignore me. I didn't even read their FAQ properly just browser through it Nil Einne 13:55, 13 January 2007 (UTC)[reply]

Composition of Solar Radiation: are gamma rays present?

Simple enough, are gamma rays a part of solar radiation?

What's solar radiation indicate about that? --jpgordon^∇∆∇∆ 15:15, 13 January 2007 (UTC)[reply]

I was going to say the same thing but surprisingly, it's not actually very clear. The two spectrum graphs for example stop in the visible wavlength, hundred nm ranges. However if you take a look at gamma ray you should notice a picture with a revealing caption. I do think the articles need work tho... Nil Einne 15:22, 13 January 2007 (UTC)[reply]

Yes, the sun does emit gamma rays. It emits radiation of (almost) all wavelengths in a planckian distribution peaking in the visible.

Just out of curiousity, does the image at Solar radiation provide the necessary answer? I don't know enough about radiation to know. --jpgordon^∇∆∇∆ 00:57, 14 January 2007 (UTC)[reply]

Not quite. It's cut off at 3 micrometers. Gamma rays are between 0.03 and 0.003 nanometers. If the graph was extended it should show some gamma rays (although very few)

3 micrometers? 30k cm^-1 is 333 nm unless I really screwed up my calculations. I.e. visible wavelengths as I said above (well okay near UV but close enough... :-P) Nil Einne 13:49, 14 January 2007 (UTC)[reply]

N.B. As I mentioned above, you can infer the sun emits gamma rays from a caption in that article:

The Moon as seen in gamma rays by the Compton Gamma Ray Observatory. Surprisingly, the Moon is actually brighter than the Sun at gamma ray wavelengths.

We can presume from the caption that the sun does emit gamma rays other wise it will say something like "Surprisingly, the Moon emits gamma rays even though the sun does not)Nil Einne 13:53, 14 January 2007 (UTC)[reply]

Why is the Moon brighter than the Sun, in gamma radiation ?

...and does the Moon emit gamma rays or simply reflect them ? StuRat 04:51, 15 January 2007 (UTC)[reply]

Cosmic rays [3]. -- Consumed Crustacean (talk) 23:47, 19 January 2007 (UTC)[reply]

Ah, so they are emitted when high energy particles slam into the Moon, that makes sense. StuRat 20:37, 20 January 2007 (UTC)[reply]

Audio file compression

I was raised in the dying days of vinyl, suffered through the Cassette tape, initially liked CDs, and have now begun downloading mainly classical recordings from iTunes. In that process I've seen the artwork, the drama, the visceral presence of the LP diminish into ghostly mp3 files and the occasional pdf attachment. In other words, I've been sandbagged into thinking that, despite getting less and less for the money, I'm somehow getting a superior product. And recently I learned that iTunes compresses audio files down to some certain rate, and that some aspects of the recording are lost in the process. I read through Compression artifacts but remain curious if someone can explain what, in general, may be getting lost in the journey from iTunes to my computer, and what a reasonably close listen to the CD v. the download might reveal, on, for example, a very recently released Deutsche Grammophon recording. Wolfgangus 17:28, 13 January 2007 (UTC)[reply]

Analog recordings vertically recorded on wax cylinders acoustically from the recording horn (using no amplification) obviously do not suffer the compression inherent in MP3. Slight surface noise and uneven frequency response are the only downsides of this method. Edison 23:24, 13 January 2007 (UTC)[reply]

Sounds minimal; not as drastic as I'd imagined. Thanks, Edison. Wolfgangus 00:55, 14 January 2007 (UTC)[reply]

Barring transmission errors, nothing will be lost from the journey from iTunes to your computer. A reasonably close listen may or may not reveal anything, since transparency is, by definition, very subjective. Oh, state-of-the-art compression can achieve transparency at 128 kbps for surprisingly many people (Wikipedia is kind-of outdated), so don't worry. --Kjoonlee 08:35, 14 January 2007 (UTC)[reply]

On that note, the subjectivity of transparency you're referring to will certainly favor me, if for no other reason my hearing isn't what it used to be. Thanks for the further input. Wolfgangus 09:58, 14 January 2007 (UTC)[reply]

If you have a proper DG disc and the same music in mp3 form, the parts I would pay attention to (if I wanted to hear what might be missing) would be the passages featuring extremely high or low tones. If you're also a Beatles fan, you might want to check out the Sgt Pepper version of "A Day in the Life". On the album (but NOT the "Blue" greatest hits album version), the main song is followed by a 15,000 Hz tone, then some garbled babbling. If iTunes is stripping high tones to decrease bandwidth issues, I'm guessing that 15 kHz bit would be gone, since many people cannot hear it anyway. I don't know offhand of a similar (known) low frequency you could examine, though that might be more important to you if your ears aren't what they used to be. Matt Deres 17:49, 14 January 2007 (UTC)[reply]

I can definitely tell between FLAC and 192kbps MP3 of the same song ripped from CD, with my non-Hifi earphone and onboard soundcard. Try listening and comparing the sound of cymbals, MP3 compression loses a lot of the detail. I've never tried iTunes since I neither own an iPod nor was it available in NZ until recently, but it's quite subjective i guess. --antilived^{T | C | G} 04:07, 15 January 2007 (UTC)[reply]

yield stress

what is the prportional limit of steal48?σy —Preceding unsigned comment added by 196.205.218.36 (talk • contribs) 18:36, 13 January 2007

Are you looking for facts about steel? Our article has links to many web pages and tables. —Steve Summit (talk) 18:46, 13 January 2007 (UTC)[reply]

sonic screwdrivers

are they any good for undoing girls' bras? —Preceding unsigned comment added by 86.142.11.215 (talk • contribs) 19:02, 13 January 2007

Since sonic screwdrivers don't exist outside of the world of Dr Who, we can only speculate on tghe basis of what we've seen in the shows. (I'm not aware of any incident in any of the shows where the Doctor has made use of his sonic screwdriver in such a way.) On the basis that the sonic screwdriver can open almost any lock, operate and repair various pieces of equipment, and even drive screws, I would suspect that it could be used to undo a bra fastener, should the Doctor feel inclined to use it for that. -- AJR | Talk 20:12, 13 January 2007 (UTC)[reply]

Slight compression of the fastener between the thumb and first two fingers is adequate for the task and can do it in a split second. Facility will develop with practice. Edison 23:27, 13 January 2007 (UTC)[reply]

Memory foam outgassing and an air purifier

Would an air purifier with a HEPA filter help clean the air of the outgassing (smell and possible chemicals) caused by newly opened memory foam? Thanks. -- Win777 19:25, 13 January 2007 (UTC)[reply]

A HEPA filter, by itself, will have little to no effect on odours or chemicals. HEPA filters remove particulates, but not gases. TenOfAllTrades(talk) 19:45, 13 January 2007 (UTC)[reply]

It took a few days to get rid of the odor of my 2" thick topper (no idea how long it would take for a full mattress). No apparent side effects, but my back thanks me for it every morning. Clarityfiend 01:02, 14 January 2007 (UTC)[reply]

Just let it air out for a few days in a garage or someplace that's easily ventilated before you use it. (I don't know why the factory can't be bothered to do this for you.) StuRat 04:43, 15 January 2007 (UTC)[reply]

Entropy vs. Energy

If entropy is energy, what is the distinction? Is energy limitless while entropy is a word to describe a measurement over time? Looking back, was there limitless energy on earth and now we're looking at the temp of the ice in the glass becoming closer to the temp of the room in terms of entropy? How does any of this reverse global warming?68.73.2.117 21:51, 13 January 2007 (UTC)[reply]

That's a lot of questions, many of which I don't understand! Maybe Thermodynamic free energy will interest you? Melchoir 22:01, 13 January 2007 (UTC)[reply]

The energy on Earth was finite. In addition Earth is an open system and is continually being provided with energy from the Sun. David D. (Talk) 22:21, 13 January 2007 (UTC)[reply]

Introduction to entropy may have clues. --Light current 23:15, 13 January 2007 (UTC)[reply]

Don't quote me on this, but entropy is almost opposite to energy. A system with high entropy has low energy. Enthalpy is a word in the back of my mind that might have something to do with this.

Entropy is essentially the tendancy of energy towards ever less usefull heat. Imagine a universe where all energy was in the form of heat and everything was the same temperature. That situation is maximum entrophy, a situation where by the second law of thermodynamics it is impossible to do any more usefull work.

Indeed, it sounds very grave. Nevertheless, the potential exists (until such time as you imagine) for the ice cube to be an ice cube if we can agree we like ice cubes and want them for TGIF parties, if there is such a thing any more. And while some may prefer room temperature beverages (no argument there) if we are losing polar ice caps -- couldn't we just make a huge white covering to reflect all that solar energy?????68.73.2.117 22:50, 14 January 2007 (UTC)[reply]

Visualization

Can it be practiced without thinking of a word to descsribe the image? If anxiety is word-related, wouldn't it be better to not use words... Say, if you're hearing your heart valves open and shut, can you redirect the thought to an Allis-Chalmers WD45 or the Dahli Lama and not feel panicky?68.73.2.117 21:57, 13 January 2007 (UTC)[reply]

Yes, I can. Edison 23:28, 13 January 2007 (UTC)[reply]

Most anxiety is not "word related", and visualization (depending exactly which meaning you had in mind) is the ability to think non-verbally, so you're better off without words.--Shantavira 09:22, 14 January 2007 (UTC)[reply]

It isn't always better to think without words though, I do that a lot and find it difficult to write about what I am thinking :) You could instead think about being calm :)Hidden secret 7 11:46, 14 January 2007 (UTC)[reply]

Perhaps this is a philosophical question like which comes first the chicken or the egg, but I'm wondering if anxiety (eg the somatic parts that are distressing) is CAUSED by thought... Too much left-hemisphere... And my question is, well, how CAN you visualize ANYthing without verbal (left brain) input? Is it possible? And don't tell me "it depends" ") 68.73.2.117 22:53, 14 January 2007 (UTC)[reply]

"Thinking about being calm" and actually experiencing calmness are quite different things. The former would necessarily involve words, imo. The latter might be induced by visualising, or being in, surroundings that are calm, safe and pleasant. JackofOz 02:44, 15 January 2007 (UTC)[reply]

Try an image that has no description in words, just a random pattern of some type. StuRat 04:41, 15 January 2007 (UTC)[reply]

Far from home?

How far, in miles, can you possibly be from home whilst remaining on the Earth's surface? Stuarthill 22:37, 13 January 2007 (UTC)[reply]

If your home is on Mars, you can't get any closer to home than a little under 34 million miles while remaining on the Earth's surface. Also when your home is on Earth, it depends on where your home is, but less so. If it is on the equator, the farthest you can get measured along the earth's surface is half the equatorial circumference, about 12451 miles. If your home is on the South Pole, the farthest spot away is the North Pole; in this case the distance is half the meridional circumference, or 12430 miles. The difference is due to the fact that the Earth is not a perfect sphere. If your home is somewhere else, the answer is somewhere in between. For some pairs of places on Earth that are about as far away from each other as possible, see our article Antipodes. --Lambiam ^Talk 11:16, 14 January 2007 (UTC)[reply]

Actually if you dug a hole directly below you home through the earth and come out the other side you would be most far away from home, on average about 7921 miles direct distance, or above for surface distnce. --antilived^{T | C | G} 04:16, 15 January 2007 (UTC)[reply]

That first reply seems incorrect to me. Any two points on the equator are separated at most by the same distance as the two poles, because you can always reach one from the other by travelling twice the distance from the equator to the pole. It's not a trivial question - what are the two points with the largest separation, on an oblate spheroid. FT2 ^{(Talk | email)} 09:17, 15 January 2007 (UTC)[reply]

You are right: I was wrong. Here is a conjecture: any point is equally far separated from its antipodal point, where the shortest path always contains a pole, and that is the farthest you can get, so that the answer is then independent from the starting point, for all oblate spheroids. Proving this, even if true, seems indeed nontrivial. --Lambiam ^Talk 17:07, 15 January 2007 (UTC)[reply]