Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

February 18

Why didn't Earth's gravity capture the asteroid 2012 DA14?

What I'm really asking is in what approach, distance, and speed should the asteroid that passed a little bit over 17,000 miles above the earth have approached earth in order for the earth's gravity to have captured it in such a way that the asteroid would have become earth's second moon? I ask because many of the planets' moons in the solar system, like the moons of Mars and many of the small moons of the Gas Giants, are actually asteroids that were captured by the planets' gravity in the distant past. 71.98.163.183 (talk) 00:06, 18 February 2013 (UTC)

I don't think it's as simple as coming in on the right velocity vector. Some complex gravitational interaction involving the Moon and Earth would need to slow it down, otherwise the speed it gains "falling" towards the Earth would be enough to make it too fast to achieve orbit. Another option is that it could skim Earth's atmosphere, and this could slow it just enough. And captured moons seem to be relatively rare, with most moons forming in place. Our Moon might be stranger, still, resulting from ejected material from Earth after an early giant impact on Earth. StuRat (talk) 00:24, 18 February 2013 (UTC)

Mars and Jupiter have greater densities of asteroids near them then out here, in the relative outskirts of asteroid-ville, and the giant planets have a Huge! capture radius and numerous moons (Ganymede is as big and massive as Mercury) to make the necessary slowdowns. Sagittarian Milky Way (talk) 01:49, 18 February 2013 (UTC)

The earth didn't capture the asteroid, but it had enough impact to change its orbital period around the sun. And keep in mind that for every Deimos or Phobos there could be thousands of asteroids that came near Mars and were not captured into an orbit. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:39, 18 February 2013 (UTC)

And it is not surprising that it was not captured into an orbit. If you just consider the two body problem of earth + asteroid, you get Kepler orbits, i.e. if the asteroid is not in an (elliptic) orbit at the start, its path will merely get disturbed by the earth, but it will not end up in an orbit around earth. For this to happen you'd need additional forces, e.g. from the moon, sun, other planets, Asteroid impact avoidance or perhaps crashing into satellites. bamse (talk) 13:08, 18 February 2013 (UTC)

So, in the case of Comet Shoemaker–Levy 9, did it kind of had all the right forces when it was captured by Jupiter in the 1960s and kept orbiting around the planet until one day the comet got so close to Jupiter and its Roche limit that the comet collided with the planet in July 1994? Would Comet Shoemaker–Levy 9 have been considered to be a moon, or at least almost a moon, of Jupiter for about 30 years? It seems that Comet Shoemaker–Levy 9 was the latest known case of a large celestial body (Jupiter) capturing a smaller celestial body. 71.98.163.183 (talk) 15:35, 18 February 2013 (UTC)

I guess you can kind of look at that comet as a model of how a planet can capture something and turn it into a satellite, but I think that the problem was that it took 2 years to revolve around Jupiter. 131.247.244.23 (talk) 15:25, 19 February 2013 (UTC)

The blue path is a hyperbolic trajectory.

• Several of the responses above are correct, but perhaps aren't making the point quite clearly enough. The default, when a body approaches a much larger body, is a hyperbolic trajectory, as illustrated in the figure -- the smaller body exits moving in a different direction, but just as fast as it came in. Very special and very unusual things have to happen in order for capture to occur. Looie496 (talk) 17:51, 18 February 2013 (UTC)
  • The OP asked why the earth didn't capture it, so maybe flip that around: What would have to happen in order for an approaching asteroid to be captured by earth's gravity and become a second "moon"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:54, 18 February 2013 (UTC)
    • But wouldn't the earth's gravitational pull be stronger than that of the sun's gravitational pull where asteroid 2012 DA14 was at its closest point to earth? Or was the gravitational pull too weak for the asteroid to be captured by earth for orbit, and why? And what was the case with comet Shoemaker–Levy orbiting Jupiter for about 20 or 30 years? P.S: There were 2 edit conflicts in a row. 71.98.163.183 (talk) 23:29, 19 February 2013 (UTC)

"Cannon fire" following meteorite impacts

Looking through reports of the 2013 Russian meteor event (we really need a better title), I've come across reports of sounds said to resemble "artillery bombardment" following the explosion. This seems to match up with similar reports from the Tunguska event, including:

After 1.5–2 minutes ... six more thumps were heard, like cannon firing, but individual, loud and accompanied by tremors.

and

After that such noise came, as if rocks were falling or cannons were firing, the earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it.

The first thought that comes to my mind is that the sounds could have been caused by larger fragments of the meteorite impacting the ground, but this seems unlikely since no fragments of the Tunguska object have ever been found, and so far no large pieces of KEF-2013 have been found either (at least as far as I know). Does anyone have a good guess as to what might cause this effect? Evanh2008 ^{(talk|contribs)} 01:15, 18 February 2013 (UTC)

The process of it breaking up can be quite explosive. StuRat (talk) 01:18, 18 February 2013 (UTC)

Yes, but this is noise following the main explosion, by at least several minutes. Evanh2008 ^{(talk|contribs)} 01:25, 18 February 2013 (UTC)

Watch the video of the shuttle breaking up. It happened in several stages. StuRat (talk) 01:47, 18 February 2013 (UTC)

The flashes from exploding meteors always travel at the speed of light while the radiated heat from the explosions travel at similar speeds. The reason why the noise is heard several minutes later is due to the fact that noise travels at the speed of sound. Therefore a noticeable delay occurs before the sound reaches the observer. 1.178.33.170 (talk) 01:54, 18 February 2013 (UTC)

I think you're still failing to understand that the sound I am describing is not the primary explosion of the object. I am well aware of the difference between the speed of light and the speed of sound. These are noises following the fireball and the associated sound. They may be reflections of that sound, but it is not simply a matter of delay. Evanh2008 ^{(talk|contribs)} 02:03, 18 February 2013 (UTC)

The 'primary explosion' of the object was never accompanied by a fireball. In some videos you can clearly make out two meteors traveling side by side, one slightly overtaking the other long before the fireball erupted. Even the smoke trail itself shows two very distinct paths that lay side by side in almost perfect symmetry. This indicates that the meteor impacted the upper atmosphere first and exploded (broke apart) before it started heating up during re-entry. Therefore it seems likely that this initial 'boom' we hear was never actually accompanied by an explosion. There are also two distinct groups of sonic booms that seem to correspond closely to the initial eruption of the fireball followed by a final, very loud sonic boom that seems to correspond to the second, smaller eruption as the meteor breaks apart into several smaller pieces. The hundreds of smaller pops and crackles could very well have been caused by the hundreds (some say 'thousands') of tiny pieces still traveling along at supersonic speeds peppering the ground. Much of this lingering noise would have been accompanied by acoustic reflections bouncing off the Ural Mountains directly underneath the path of the meteor. The mountains themselves would have acted as a natural sounding board. 1.178.161.116 (talk) 05:26, 19 February 2013 (UTC)

I heard what you are talking about on the video. One animation that I saw had it breaking into one big piece followed by five smaller ones, but I don't know if that is accurate. The smaller booms could have been from the smaller pieces. Just my guess. Bubba73 ^{You talkin' to me?} 02:13, 18 February 2013 (UTC)

It could have been explosions of bits separated by the main explosion, but more likely the subsequent bangs were sound reflections. I have a book describing a test nuclear explosion in the South Australian desert. At distances of 200 - 300 km or or so, three bangs were heard - the primary shockwave travelling outward at ground level first, then a boom that was due to reflection of sound from the upper atmosphere (ie longer path), then a rumble from reflections off prominent ground features. A high altitude explosion could be expected to produce a degree of reverberation from reflection from the ground and high altitude velocity of propagation changes. Air temperature, and thus velocity of sound, reduces with increasing altitude until a certain height, whereupon temperature increases again. Wickwack 124.182.151.79 (talk) 01:56, 18 February 2013 (UTC)

Ah, that's very interesting. I find the sound reflection idea much more plausible than my idea of fragment impacts. Thanks! Evanh2008 ^{(talk|contribs)} 02:03, 18 February 2013 (UTC)

And the 30,000,000 tons TNT of the Tunguska event is alot of boom, even spread out. That is the size of 15,000 atomic bombs or millions of Oklahoma Cities. Sagittarian Milky Way (talk) 02:01, 18 February 2013 (UTC)

Every time I have tried to type here got an edit conflict :) so here is a short Q: Why do all the meteor videos start with a bang? ie there is no lead up sound, no build up to the bang, just silence then boom, then diminishing fireworks for a minute or so. Possibly because it broke apart almost immediately - two trails appear almost right from the start. Interested in any thoughts. Zeb253 (talk) 02:04, 18 February 2013 (UTC)

Because the film editor thought it had more impoect if it started with a good bang? Wickwack120.145.150.250 (talk) 02:14, 18 February 2013 (UTC)

Here is one video of the sound I am talking about - 30 seconds of near silence followed by the big bang and fireworks - no lead up to the big bang. http://www.youtube.com/watch?feature=player_embedded&v=MKx97csfPy0# - possibly part is the mics adjusting the sound level but still it does start suddenly but not end suddenly. Zeb253 (talk) 02:20, 18 February 2013 (UTC)

Evanh2008 - There is certainly a big bang at the start of the audio - my guess for the canon fire and fireworks after the bang is a combo - the meteor broke up in explosive stages (perhaps one big one and many more subsequent ones as the pieces got smaller and smaller), and of course it happened at such a speed that sonicboom/shockwave add to the noise, plus there will be some echo too. Zeb253 (talk) 02:10, 18 February 2013 (UTC)

Our Russian meteor article tells us that it was "[m]oving at a speed of 15 km/s to 18 km/s (34,000 mph to 40,000 mph)". If this speed is correct, it is about Mach 44 (assuming speed of sound at sea-level and 20°C and thus 761 mph). Our sonic boom article explains that "[s]everal smaller shock waves can, and usually do, form at other points on the [aircraft meteor]". Hence the multiple sounds heard. In addition, that article also says "[as] those who have witnessed landings of space shuttles have heard, when the aircraft is nearby the sonic boom is a sharper 'bang' or 'crack'. The sound is much like the 'aerial bombs' used at firework displays" --Senra (talk) 14:10, 18 February 2013 (UTC)

• Don't forget, it was traveling at about Mach 45, whereas the sounds that it was making traveled at Mach 1. So, all of the noise that it made along it's path would take a while to "catch up" and reach observers who were near the main explosion later in the path. North8000 (talk) 17:45, 18 February 2013 (UTC)

• According to NASA:Russia Meteor Not Linked to Asteroid Flyby 02.15.13: "The meteor entered the atmosphere at about 40,000 mph (18 kilometers per second)", "its estimated mass [is] 10,000 tons", "... the event, from atmospheric entry to the meteor's airborne disintegration took 32.5 seconds" and "Based on the duration of the event, it was a very shallow entry". I cannot calculate its terminal velocity but it would be considerably less that Mach 44 --Senra (talk) 21:08, 18 February 2013 (UTC)

I wouldn't want to original-research this one without having at least five tapes with GPS coordinates for the location each one was taken and accompanying video so that they can be precisely timed based on the point where the trail turns from very wide to quite narrow. But maybe somebody will post that. :) Wnt (talk) 20:01, 18 February 2013 (UTC)

Historical accounts of past meteor events report the same phenomenon. A good example is the meteorite fall that occurred near Hatford, then in Berkshire (now in Oxfordshire), in England on 9 April 1628. Accounts of that are given here and here. The first link is a contemporary account as later published in Chambers's Papers for the People (1850) - not sure when it was first published. The second link (a pdf from an Oxfordshire museum) gives what it says are the only two known contemporary accounts of the Hatford meteorite fall. What I'm quoting here is from the museum's quote from that anonymous 1628 account (the wording in the Chambers's Papers for the People version is different and includes other details):

"In an instant was heard first a hideous rumbling in the air, and presently after followed a strange and fearful peal of thunder; it maintained the fashion of a fought battle. It began thus: first, for an onset, went off one great cannon as it were of thunder alone, like a warning-piece to the rest that were to follow. Then, a little while after, was heard a second; until the number of 20 were discharged, or thereabout. In some little distance of time after this, was audibly heard the sound of a drum, beating a retreat. Amongst all these angry peals shot off from heaven, at the end of the report of every crack, a hissing noise made way through the air, not unlike the flying of bullets from the mouth of great ordnance, and by judgement were thunderbolts; for one of them was seen by many people to fall at a place called Bawlkin Green..." - anonymous leaflet on the Hatford meteorite fall of 1628

That all sounds very much like what was observed and heard for this meteorite fall in 2013. Carcharoth (talk) 20:26, 18 February 2013 (UTC)

Very interesting indeed, thank you. I note that on this video you can hear the multiple explosions persisting for at least 90 seconds after the initial detonation. The physics of the sound are probably going to keep some researcher busy for a long time... Prioryman (talk) 20:46, 18 February 2013 (UTC)

tempature of LED

On the wikipedia page for Light-emitting diode (LED) it states as one of the advantages, "Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED." My question is what does very little heat mean? How hot does the inside get? — Preceding unsigned comment added by 69.115.221.5 (talk) 03:27, 18 February 2013 (UTC)

While the total heat generated is low, each LED is tiny, so the heat inside it might be more than you'd think. StuRat (talk) 05:19, 18 February 2013 (UTC)

An incandescent globe operates essentailly as a black body radiator. The filament is heated by the electric current to a white heat temperature - 3800 deg C or higher. In consequence, most of the energy is emitted as infra red i.e., heat, and only a small fraction of the energy is emitted as visible light. In contrast, LED's operate completely differently, emitting visible light photons as electron- hole pairs collapse. Heat in a LED is only generatted by the current floowing through the electrical resistance and is not an essential part of the light emitting process. Hence the fraction of total energy emitted as light in a LED is very high compared to incandescents.

LEDs must be operated at an internal temperature less than the limit imposed by the chemically doped crystal structure - usually taken as 200 deg C. However, the reliability of LEDs, as with any semiconductor device roughly doubles for each 10 C drop in temperature. For this reason, LEDS should generally be opereted at an internal temperature of around 55 C or less.

Keit 120.145.52.14 (talk) —Preceding undated comment added 11:25, 18 February 2013 (UTC)

While I don't disagree with the majority of Keit's post, I'd note that given the demands of lighting systems, particularly replacement bulbs for existing fixture, many LED manufacturers seem to be coming round to a higher limit usually 85 degrees C maximum for the internal junction temperature under normal operating conditions. Cree bins or rates most of their LEDs at this temperature[1], as does Philips/Lumileds [2] (which they call real world operating conditions) and actually I believe most reliable manufacturers now do so, rather then the ridiculous 25 degrees C they used to use. You can also see this Osram document which also recommends a similar thing [3] and interesting enough the Indian Railways seems to have specific requirements at 85 degrees C [4]. This does have negative effects on lumen maintenance and lifespan in general, as well as in performance but as I said, thermal management is not always easy, particularly when used in replacement style bulb. (And of course once it's binned at that temperature, if it meets your requirements the fact it could be better if cooler is not necessarily a big concern. Of course since the colour tends to change and the changing performance means the brightness changes, you do want to have a good idea of what the junction temperature is likely to be.) The absolute maximum BTW tends to be in the 120 - 150 degrees C range. You may also be interested in Thermal management of high-power LEDs. Nil Einne (talk) 12:28, 18 February 2013 (UTC)

Water heater producing hydrogen

From the instruction manual of my washing machine:

“ WARNING: Under certain conditions, hydrogen gas may be produced in a hot water system that has not been used for 2 weeks or more. HYDROGEN GAS IS EXPLOSIVE. If the hot water system has not been used for such a period, before using the washer, turn on all hot water faucets and let the water flow from each for several minutes. This will release any accumulated hydrogen gas. Hydrogen gas is flammable; do not smoke or use an open flame during this time. ”

How would an unused "hot water system" produce hydrogen gas, and is this a real hazard, or is it something that happened to somebody once so the lawyers now insist on a warning? --Carnildo (talk) 04:23, 18 February 2013 (UTC)

When two different metals are connected by a conductor, an electrochemical reaction occurs which will corrode one of the metals. In the case of a steel water heater tank and copper pipes, it is the steel that corrodes. To slow this process down, water heaters have a replaceable sacrificial anode rod that corrodes instead of the steel. High end water heaters often have two rods.

The most common rod material is magnesium. Magnesium sacrificial anodes have the advantages of not dropping debris into the tank and not expanding when they corrode. However, they can release hydrogen gas as they corrode. How much depends a lot of the chemistry of your water. Of course the warnings are for the worst case. When the water contains sulfur, bacteria can grow that produces hydrogen sulfide gas (that's the one with the "rotten egg" odor).

Aluminum anodes also prevent corrosion and do not produce hydrogen gas, but they expand as they corrode, often becoming larger than the opening they were inserted through. Also, debris from the aluminum anode drops into the bottom of the tank and can clog the hot water system. Also, decide for yourself whether you buy the stories about aluminum in the diet and Alzheimer's.

Zinc rods are really aluminum rods with a section of zinc The zinc lessens the odor of sulfur within the water. Otherwise they act kike any other aluminum rod.

If you have a bacteria problem, the first step is to set the temperature on your water heater to high for three days. Be careful not to scald yourself when using the faucet or shower. Another effective way to fight the bacteria is to oxygenate the water with hydrogen peroxide. Anaerobic bacteria thrive where there is little or no oxygen, and the hydrogen peroxide creates an oxygenated environment. One pint of hydrogen peroxide per forty gallons of tank capacity should be enough. Keep open flames away just in case there is some oxygen buildup. Run all the hot water taps until they run hot and then turn them off Let the water stand for two to four hours then run each hot water tap for about five minutes to flush the peroxide. Sometimes you have to repeat this several times until you kill all the bacteria. --Guy Macon (talk) 05:22, 18 February 2013 (UTC)

(ec) Galvanic action between different metals can set up a slight electric field, which might decompose water, by electrolysis, into hydrogen and oxygen. I would expect a microscopic amount, but, if it accumulates, it might add up to something substantial. StuRat (talk) 05:25, 18 February 2013 (UTC)

It's not electrolysis, which turns water into hydrogen and oxygen. It is anaerobic galvanic corrosion, which turns water and magnesium into hydrogen and magnesium oxide. This process is used in industry to create bulk hydrogen without the high electricity costs of electrolysis. Basically, you put magnesium in a 100% steam atmosphere and set it on fire as the steam flows past. As it burns it creates magnesium oxide and hydrogen gas. (Steam works better than water, because it avoids magnesium hydroxide forming). --Guy Macon (talk) 07:19, 18 February 2013 (UTC)

Why not use same metal in the whole hot water system? Electron9 (talk) 08:51, 18 February 2013 (UTC)

Most water heaters are steel to keep the price down, but there are copper water heaters that would match copper pipes. The problem is that a household water system needs to connect with the rest of the world, and re-plumbing your entire city with copper is impractical, so you would still have galvanic corrosion where your copper pipes connect to the water main. The answer to that would be a sacrificial anode somewhere in the system.

Plastic pipes are an interesting variant; you would still get an electric current between, say, a copper faucet and a steel water tank connected by a long plastic pipe, but the long column of water would have significant resistance, thus lowering the current and the corrosion. --Guy Macon (talk) 14:15, 18 February 2013 (UTC)

The girl with an IQ of 161

I've never understood what an IQ actually means. Using this girl as an example, is she able to read this entire reference desk page and understand everything everyone is discussing? I'm assuming she still has to "learn", but maybe her capacity for retaining and recalling information is advantageously high? Why is a high IQ usually equated with science and math, anyway? Can someone have a (technically) high IQ, but have no interest or even comprehension of higher and complex sciences and mathematics on paper, but be brilliant at something else? Mozart probably had a high IQ, I'm guessing? He could absorb music and spit it back out, but if he were alive today, would he have also been designing rockets on the side? Do polymaths have high IQs? What about people who were extremely good at one thing and one thing only, like someone who has an uncanny ability to learn and speak languages fluently, but more or less isn't good at anything else? – Kerαunoςcopia^◁_galaxies 08:34, 18 February 2013 (UTC)

Oh, and how much of IQ do you think is affected by impatience? – Kerαunoςcopia^◁_galaxies 08:34, 18 February 2013 (UTC)

See g factor (psychometrics) for the hypothesized quantity that IQ is supposed to measure. The extent to which such a thing exists is hotly debated (you'll probably get a lot of responses that say there's no such thing, because, apparently, that's what the "good" people are supposed to think </snarky aside> ). Even if there is such a quantity, of course, IQ, like any test, is an imperfect measure of it. --Trovatore (talk) 08:38, 18 February 2013 (UTC)

I happen to believe IQ tests are laughable metrics, but it has less to do with any moral judgement on equality and more to do with coming from a background in the cognitive sciences and knowing the difficulties involved in quantifying mental phenomena (though in the case of IQ tests I daresay anyone with common sense ought to be perplexed out how subjective weighting of different mental tasks is supposed to yield an absolute) and in knowing the well-documented origin of such tests in pseudo-science and general quackery (usually of the highly racist variety). This is one subject I typically can't help weighing in on -- the disconnect between the actual empirical study of the mind by those in a field of relevance and the perception amongst people who are not (even those who are undoubtedly are extremely gifted) can be pretty profound and fascinating -- but my time is limited just now, so it will have to wait until tomorrow. In the meantime, to anyone interested in the subject, an excellent primer is Stephen Jay Gould's The Mismeasure of Man, which looks in detail at the methodology of the early IQ tests in the context of the broader trend towards ridiculous psychometrics of the time, including craniology and so-forth. Of course, IQ tests have come a long way in trying to eliminate biasing elements with regard to social factors, but they haven't made much progress in terms of improving upon the general subjectivity in their basic assumptions and priorities between mental tasks, which is why they are of little interest to anyone doing genuinely empirical work in exploring the brain's (or the mind's) capabilities. Snow (talk) 10:17, 18 February 2013 (UTC)

Gould is exactly one of the ones I had in mind with my "good people" comment. I got a very strong impression, when reading Mismeasure, that while he certainly made valid criticisms of the scientific objectivity of the ones he criticized, his own was equally suspect. --Trovatore (talk) 10:21, 18 February 2013 (UTC)

It's an interesting book for him; most of his other supposedly broad-audience works I've found to be pretty dry. He obviously felt impassioned about this subject. But for all of that, I don't know that I ever felt his objectivity was flawed in that particular work. He certainly busts some balls, but it's hard to find fault with his arguments, as well documented as he makes them. Snow (talk) 10:26, 18 February 2013 (UTC)

To me it comes across as a straight polemic. I cannot claim to have studied the topic in any depth, but I find it very difficult to trust the objectivity of a worker who writes polemics on the subject he studies. His argument that g is nothing but principal component analysis is particularly facile in my view. --Trovatore (talk) 10:30, 18 February 2013 (UTC)

Hold that thought, back to discuss this in greater detail tomorrow. (All in the interest of more fully answering the OP's inquiry, of course! :) Snow (talk) 10:36, 18 February 2013 (UTC)

(Trovatore, you just committed the unspeakable crime of having an unmatched tag.) The g factor, which IQ tests are designed to measure, is the "average" of a wide variety of abilities that make up intelligence. As an analogy, suppose a company wanted to evaluate how good a potential employee is. It might consider a wide variety of factors that affect "goodness". How much experience does he have? How patient is he? How logical is he? Does he have good people skills? Motivation? Passion? Flexibility with work hours? All of these factors are part of his goodness, but someone with very high goodness doesn't necessarily score highly in every aspect, and someone with very low goodness could score highly on a few aspects. The same is true with IQ tests. Getting a high score is far easier if you're good at everything, but you could be absolutely hopeless at a few things and still score highly if you're a genius at everything else. --140.180.243.51 (talk) 09:19, 18 February 2013 (UTC)

IQ is the attribute measured by IQ tests. HiLo48 (talk) 10:23, 18 February 2013 (UTC)

In much the same way ghosts are the things pursued by ghost hunters. ;) Snow (talk) 10:28, 18 February 2013 (UTC)

Yes, an excellent analogy. HiLo48 (talk) 10:35, 18 February 2013 (UTC)

Except, IQ strongly correlates to performance on a wide range of other skill-tests, from rifle marksmanship to average salary over the person's entire career. In this August 2010 discussion, I attempted to refute the point that IQ is meaningless. I will concede that IQ is not the only factor in human cognitive performance, but it is a reliable and repeatably-measurable metric. The accuracy and precision and repeatability of modern tests are all surprisingly high. And when judging people in the statistical aggregate, which is often necessary for large organizations, it can efficiently summarize other performance metrics. If misused or misinterpreted, the data-point can lead to very invalid conclusions. But it's not fair to say that IQ is pseudoscience. On the whole, it is a measurable, quantifiable, repeatable metric. Any conclusions drawn from this metric are falsifiable and can be substantiated by experiment. Nimur (talk) 13:25, 18 February 2013 (UTC)

Nimur, do you have citation for the IQ-marksmanship correlation? I'd like to read more about it. It's not too surprising, since IQ is correlated with height.Dncsky (talk) 14:39, 18 February 2013 (UTC)

Yes, in the discussion I linked above, or directly linked here: Whole and Part Methods in Learning a Perceptual Motor Skill (1954). The study compared some three hundred infantrymen at Fort Knox; trained some in marksmanship using Method A and others using Method B; and analyzed the results. A secondary analysis of the same data treated the the training method a a null factor, and instead compared the marksmanship results against each man's previously-measured intellectual aptitude. And finally, they analyze whether higher-intelligence riflemen learn better using Method A or B. There is no reason to slander the intellectual aptitude of "army guys." Completion of an ASVAB (part of which is essentially an IQ test) is mandatory for most recruits to most branches of the armed services in the United States; and the intellectual entrance requirements for many career military tracks are as stringent as those for some universities. At the very least, the armed forces have standardized empirical data, which can be used to objectively analyze their recruits: many universities do not even have such data, or rely on a third-party corporation to provide it. Nimur (talk) 15:01, 18 February 2013 (UTC)

What a jolly good read, thanks. I have retracted the joke; it was made in poor taste and inappropriate for the RD. A certain Australian must be rubbing off on me. For the record, I will soon be one of the "army guys" and the joke was intended as self-deprecating humor.Dncsky (talk) 15:10, 18 February 2013 (UTC)

Yeah, but consider an anologous Athletic Quotient, which is measured by a test which inncludes things like a 100 yard dash, a bench press, ability to catch a fastball, triathlon, etc. I think the average person would see that there is some validity in such an overall measurement, but would realize that it's really looking at a wide variety of individual skills, which are only slightly related; if you have some sort of neuromuscular disorder, for instance, you'd do badly overall, but marathon running and weight lifting skills probably aren't that tightly correlated. Same for IQ; if you brain is defective, you do badly overall, but there's no real evidence that there is a specific function used in visualizing what the object in a picture would look like if rotated and also used in reading comprehension. Gzuckier (talk) 14:57, 18 February 2013 (UTC)

As I mentioned above, IQ is measurable and tests can be designed that stand up to scientific scrutiny. That does not equate to "any conclusion about IQ is immediately true." There are many hypotheses about IQ that can be tested and proven false. If your hypothesis is that IQ correlates (or does not correlate) to performance on spatial reasoning tasks, then I am not sure about the answer; but I am sure there are experiments that have tested that hypothesis and published their findings. Nimur (talk) 15:01, 18 February 2013 (UTC)

• The issue with IQ tests is that they are statistically valid without necessarily being individually deterministic. That is, IQ tests are valid when averaged across wide swaths of population: for enough people, they seem to be roughly useful predictors of certain aptitudes and skills they may have. If you average out IQ results over many millions of people, then the outliers get averaged out. That is, there are going to be some people for whom the IQ test is woefully wrong in terms of acting as a predictor of anything. These people are common enough that, anecdotally, enough people will know someone like this, to make it seem like the IQ test is worthless. And for that person, it is. However, when that person's results are averaged into "all of humanity", it doesn't make much of a difference at all. So, are IQ tests useful? Yes, except when they aren't. --Jayron32 16:24, 18 February 2013 (UTC)

As a random comment, not an answer, I would suggest that the layman's terms of "dull" and "bright" are about as useful. IQ measures something, but just what is hard to say. If you do a chemical reaction and the mixture turns some color, sometimes you can surmise something, but it doesn't really tell you much for sure, and that is about what IQ tells you. It is a single scalar measurement of a very complex matrix of many kinds of data. Wnt (talk) 19:57, 18 February 2013 (UTC)

Wnt just neatly and concisely said what may very well have taken me (is about to take me?) several paragraphs to voice. It's a bit of a case of not seeing the forest (the concepts in this case) for the tress (the raw mathematical data and various trends found therein). Nimur makes some decent arguments above as to why the field cannot be said to be completely without structure, but statistical self-consistency is not the only measure by which the extraordinary claims of this field must be analyzed. That people or sample populations can repeat similar testing scores under similar conditions is not in itself surprising. What said results actually say about the nature of intelligence and where people rank in some abstract spectrum is another matter entirely. Though the specific claims that are made may vary some between tests, they mostly share in common an assumption that "this is a reasonable measure of some form of general and/or practical intellect." -- an assumption that is just not established by any line of reasoning that doesn't rely heavily on subjective assesments. Oh, look at that, managed to keep it to one. :) Snow (talk) 00:42, 19 February 2013 (UTC)

In 1967 I applied for a job with the Australian Government Public Service. At that time, entry was by sitting a 3-part exam. When I sat it, there were about 1500 applicants for 120 jobs. The exam results were ranked 1 thru to 1500, 1 = highest score, 1500 = lowest score, and they sent job offer letters to the folk with rankings 1 thru 140, knowing from experience that about 20 would not take up the job offer. No interviews were conducted. The three parts to the exams were a) Mathematics, pitched at about 1st year high school level, b) General knowledge: multi-choice - typical questions were things like From what direction does the sun rise in the morning? East, West, North, South; Is the differential in a motor vehicle connected to - engine, radiator, gearbox, prop-shaft; c) A raven's style IQ test. I should think that every one would have done well in Part A and B, so the IQ test was probably the decider. I was ranked 37, so I got a job. They sent a list of all 140 successful applicants, with their ranking, to each succesful applicant. I still have my copy, and I now have known most of the succesful applicants for 46 years. Some turned out a dead loss. Some are now top leaders in major businesses. So how does the ranking correlate with the career success? Answer - no correlation AT ALL! And nothing I have experienced in my career ever since has indicated to me that IQ and aptitude testing has any value at all. Ratbone 124.178.182.45 (talk) 00:21, 19 February 2013 (UTC)

I don't know how you compared the success of those selected against that of the ones not selected. For quite a few jobs doing an interview after selecting candidates that way actually reduces the number of good outcomes compared to not doing any interviews so I wouldn't dismiss it so quickly. There's no 100% successful way to select people to employ - and in fact even selecting only the most suitable is often a wrong thing to do as one wants a mix with some people willing to do the nitpicky stuff and others to have grand ideas and others who just hold a team together properly. Dmcq (talk) 13:06, 19 February 2013 (UTC)

If you read carefully what I said, you'll see that where I said there was no correlation between ranking and carrer success, I was referring to the subset of candidates who received job offers - these are the people I got to know as work colleagues and friends. Having said that, I do know three people, who were schoolmates, who were not given job offers (and were ranked further down on the list), and all three have had careers that indicate they should have being given an offer. One was ranked at about 1000 as I recall. One is a senior police detective, one is head of a plumbing firm emplying hundeds of people, and one became a grocery store manager.

In my careeer, which includes leaving govt service after 10 years and becoming a professional engineer and later becoming a manager, I have plenty of experience of working with people selected by interview conducted by others, people selected by interview conducted by myself, and plenty of experience where selection was based on interview backed up by IQ/aptitude testing. Interviewing is certainly not perfect, and a lot of managers/selectors don't know how to run interviews. Never-the-less, interviewing is far far better than any other method. When I interview candidates for jobs, I try and create a relaxed atmosphere and put the guy/girl at ease - pretty much have a friendly conversation, getting them to tell me what they've done, problems they've solved, things they are proud of. People they admire and why. I'll ask them why they applied for the job. At some stage, I'll switch and put them under pressure, hit them with questions to see how they think. Then I'll back off. After the formal interview, I'll walk them around the plant, unless they are hopeless. If they are good, I'll find some excuse to talk to one of the technicians, and get the candidate involved in the conversation, which may range from where is a good place to buy pizza to whatever the tech is working on. I seldom make a mistake on who to hire. I worked for one company that had a policy of backing up interviews with IQ/aptitude testing done by an external consultant. The consultant provided a detailed report based on raven testing and another IQ test that I found out was supposed to screen high school students for higher study. These detailed reports never got it right, and fortunately we ignored them. Ratbone 124.182.51.4 (talk) 01:29, 20 February 2013 (UTC)

As to IQ it is designed as a measure of mostly problem solving ability and as people said above doesn't measure a number of important factors like being able to get on with others. Intelligence tends to be a bit more integrated than athletic ability, but even so whilst it is true that a top class runner won't shine against a top class weightlifter but compared to your average man on the street they probably still would wipe the floor with them at most things athletic. IQ can be thought of as an equivalent of measuring general fitness by seeing how people get on with a range of athletic tasks. Dmcq (talk) 13:06, 19 February 2013 (UTC)

Not really. It's more like trying to measure athletic fitness by measuring things like how much weight you can lift by bending your big toe, or how much air you can pump by fluttering your eyelashes. There are IQ tests and there are IQ tests, Stanford Binet and Raven's Progressive Matrices being probably the most well known and most used. SI has perhaps some merit, not much. Raven's just tests your ability to pick visual patterns and has no bearing on anything in the real world at all, not withstanding what some psychologists would have you believe. And it is amazing what rot some psychologists read into Raven scores. Ratbone 58.170.151.23 (talk) 12:19, 21 February 2013 (UTC)

Disease transmission from sharing a cup?

What is the likelihood of contracting a disease, illness or infection from the sip of a shared cup at a social gathering in church? 140.254.226.238 (talk) 15:20, 18 February 2013 (UTC)

Yes, I recognize that some churches individualize cups. 140.254.226.238 (talk) 15:24, 18 February 2013 (UTC)

I'm curious about this too, always seemed instinctively to be a really bad idea - perhaps some sort of alcohol content helps kill the germs, hopefully someone can find us a study --_nonsense ferret 17:01, 18 February 2013 (UTC)

I don't think the alcohol in church wine is sufficient for sterilization, you'd need something more like vodka. Also, as I note below, the rim may carry the microorganisms, and not have any wine on it. StuRat (talk) 17:09, 18 February 2013 (UTC)

Do you think churches should use something like vodka or individualize cups instead? 140.254.226.238 (talk) 17:12, 18 February 2013 (UTC)

Individual cups, yes. Straight vodka, no. That would burn people's throats. (Enough alcohol to kill bacteria cells also kills the cells lining your throat.) StuRat (talk) 17:19, 18 February 2013 (UTC)

Well, if you can distill wine and count it as valid for sacramental use when it condenses, perhaps one could merely boil the alcohol and the congregation could take inspiration from the ... :) Wnt (talk) 19:50, 18 February 2013 (UTC)

Well, quite a few diseases can be transmitted by saliva, especially if the recipient has a cold sore or chapped lips, allowing the bacteria to enter thru a crack in the skin. The previous person to use the cup might have had similar lip problems, and have bled on the cup rim. Exposure to air quickly kills many microorganisms, but the time between sips may not be long enough. Inside the mouth and throat, there may be other breaks in the skin. Once the sip makes it to the stomach, disease transmission is unlikely, as stomach acid is sufficient to kill the small bacteria load. StuRat (talk) 17:04, 18 February 2013 (UTC)

This is actually much closer to "medical advice" than many of the redacted topics - however, public health seems to be something traditionally left to guesswork (and the will of God). I would think of meningitis (e.g. Neisseria meningitidis, Streptococcus pneumoniae) and (if cleanliness lags behind godliness) hepatitis A transmission, among other things. Wnt (talk) 19:48, 18 February 2013 (UTC)

• If anyone is interested in references that address this question (I see Wnt has supplied some nice wikilinks for diseases during my EC), please see the study entitled "Survival of bacteria on the silver communion cup", here [5]. The article is on Jstor, and should be freely available to the public. I found this reference by searching google scholar for /disease transmit cup/, and this came up as the third hit. Granted, the work is old, and there are probably much more recent studies. These can be found by perusing the list of works that cite this one, etc. SemanticMantis (talk) 20:12, 18 February 2013 (UTC)

Should be, alas is not. But you're right I should have looked more carefully. Even so... I imagine every species of bacteria is potentially its own experiment. Anyway, respected sites [6][7] support cup sharing for meningitis. Wnt (talk) 22:17, 18 February 2013 (UTC)

Ok, my link assumes institutional access, which we obviously don't all have. However, I believe anyone can get to it if they register (for free) at Jstor's "register and read" program, here [8]. From there, the title quoted above should get you to the paper. (and the "no refs" comment was not directed at anyone individually, and you at least did give some relevant wikilinks). SemanticMantis (talk) 22:26, 18 February 2013 (UTC)

And to save time for the only mildly curious, the study concludes "Evidence is presented which indicates that bacteria swabbed on the polished surface of the silver chalice die off rapidly. Experiments on the transmission of test organisms from one person to another by common use of the chalice showed that approximately 0.001 % of the organisms are transferred even under the most favorable conditions; when conditions approximated those of actual use, no transmission could be detected. Only small numbers of bacteria from the normal mouth could be recovered from the chalice immediately after its use by 4 persons. It is concluded that in practice the silver communion cup is not an important vector of infectious disease" -- But I'm not sure how this conclusion would hold up under modern scrutiny. SemanticMantis (talk) 21:44, 18 February 2013 (UTC)

Yea, the main thing missing from that statement is how long they waited afterwards to do the test. Since there may only be seconds between uses of the cup, the test would need to be done within seconds to be valid. StuRat (talk) 21:51, 18 February 2013 (UTC)

They figured out that 5 minutes was too long to wait. So they had person A drink, then immediately person B, then took samples within a minute. (I'm not quoting directly because of formatting issues, the quote above took me several annoying minutes. If you don't trust my paraphrasing, please register and read the paper ;) SemanticMantis (talk) 22:31, 18 February 2013 (UTC)

I also should note that their conclusions are based on the treatment wherein the cup was wiped with a cloth between drinkers (which I think is common practice in USA christian churches that have a communal communion cup) -- so that this claim of "not a big risk" is specific to communion cups which are wiped, not drink sharing in general. As Wnt points out above, several diseases are known to propagate via casual drink sharing. SemanticMantis (talk) 23:47, 18 February 2013 (UTC)

Who drinks wine at church? It's blood. --Onorem♠Dil 12:29, 21 February 2013 (UTC)

Water jet that pops up after somethings drops in water

When something is dropped in water, a thin jet rises up (like this). What is the technical name for it? I cannot recall. It was something like williamson jet. Does anyone here know the right name? —  Hamza  ^{[ talk ]} 15:32, 18 February 2013 (UTC)

According to Wikipedia's page on Drop (liquid), it looks like it's called a "backjet". 140.254.226.238 (talk) 15:37, 18 February 2013 (UTC)

Resolved

Thankus Maximus. —  Hamza  ^{[ talk ]} 16:08, 18 February 2013 (UTC)

Sulfuric acid and nitric acid for cleaning glassware

In Introduction to Organic Laboratory Techniques [9] two solvents are suggested for cleaning glassware:

1. Acetone

2. A mixture of concentrated sulfuric acid and concentrated nitric acid

Isn't #2 kinda dangerous since it could lead to nitration and thus explosive compounds like RDX and TNT?

Googling "cleaning glassware sulfuric acid nitric acid" gets me plenty of other textbooks suggesting the exact same formula [10][11], albeit as an alternative for the standard chromic acid. Dncsky (talk) 16:50, 18 February 2013 (UTC)

Geez, if you need to use dangerous chemicals like that the clean your glassware, maybe you'd best just replace it. I sure wouldn't want to inhale those fumes, either. StuRat (talk) 16:57, 18 February 2013 (UTC)

The glassware under question typically isn't a set of Ikea bowls. Depending on the reaction vessel under consideration, you're talking $50 or more each - sometimes much more if it's a specialized piece of apparatus. "Toss and replace" is impractical if there is a simple and inexpensive way of cleaning them. Sulfuric & nitric acid aren't all that hazardous if handled properly, and "wouldn't want to inhale those fumes" isn't an issue if you have a exhausting fume cabinet, as would most who are doing such procedures. - Regarding nitration, yes, that can lead to explosive compounds, but generally you would remove most of the organic material by soap&water/solvent washes prior to the acid bath. The acid bath is primarily to get rid of residual contamination. Only a small amount of nitrated compounds will be made, they'll be dissolved in an excess of solution, and there's enough excess nitric acid that they'll likely be completely oxidized. Care must be exercised, though. Consult with an experienced organic chemist (most love to talk shop, especially if you're paying for the beer) before attempting. - That said, using concentrated sulfuric and nitric acid isn't all that common in my (limited) experience. Perhaps if you have some persistent contamination and nothing else works. Most organic labware gets cleaned with soap&water and an acetone rinse. If that doesn't work, a soak overnight in dilute acid is usually done. Dilute sodium hydroxide baths are sometimes also used, although that can etch glass and ruin ground glass joints, so base baths are typically used sparingly. As Pavia says, the sulfuric/nitric mix would only be for "troublesome stains and residues that adhere to the glass despite your best efforts". -- 67.40.213.4 (talk) 17:56, 18 February 2013 (UTC)

OK, but basic test tubes and flasks can be replaced cheaply. StuRat (talk) 18:02, 18 February 2013 (UTC)

Test tubes are nearly always designed to be disposable.. especially the smaller ones that you fit into fraction collectors. Flasks on the other hand can be quite a bit more expensive, especially precisely calibrated volumetric flasks. Back to the original question, as 67 pointed out you'd really only be using this sort of acid rinse in a functional hood so the fumes aren't much of an issue. Not to mention, we do keep both dilute sulfuric acid and dilute nitric acid in the teaching labs here, it can't be too hazardous if they let freshman/undergrads use it in genchem. For really persistent contaminants you can use concentrated nitric acid; I've certainly cleaned cuvettes that way on occasion. It's certainly more cost effective than replacing a quartz cuvette! And yes, base baths will etch glass rather quickly, so as already stated above you wouldn't want to use them on anything with joints or fittings. (+)H₃N-Protein\Chemist-CO₂(-) 19:12, 18 February 2013 (UTC)

Cleaning classware with nitric is on par with lighting a barbecue with liquid oxygen [12]. Spectacular but dangerous. Don't try it at home folks – in your neighbors garage yes – it invokes a lot of 'wows' etc (followed by the sound of sirens from the emergency services ) but not in your own house please.--Aspro (talk) 22:55, 18 February 2013 (UTC)

Note, "concentrated" is of course a relative term. Nowhere did I say that I was cleaning cuvettes with fuming nitric acid. I think it's a little silly to make such a big deal about nitric acid without even factoring in concentration. Yes, you probably don't want to pour even moderately concentrated nitric on exposed skin or bad things would happen.. but I doubt many solvents would pass the "I can pour it on my arm without adverse affects" test, so that's an odd safety requirement. (+)H₃N-Protein\Chemist-CO₂(-) 02:11, 19 February 2013 (UTC)

I'd compare it with things normally used to clean glassware, like detergent and water (distilled water in this case). In that context, these cleaning methods seem quite extreme. I suppose they have their place, on expensive items which can't be cleaned in any other way, but their use should certainly be limited. StuRat (talk) 02:17, 19 February 2013 (UTC)

Not limited. No reason it should be either. We used to keep a garbage pail of dilute acid for the first day's soak and a garbage pail of sodium hydroxide for the second day's soak then a day in the oven to dry. For every single piece of glassware. Chemists work with far more dangerous chemicals all the time. Which is why we have lab coats - and gloves, safety glasses, fume hoods, eye washes, emergency showers, acid spill kits, mercury vacuums, gieger counters, lead aprons, inert atmospheres, etc. Rmhermen (talk) 15:52, 19 February 2013 (UTC)

Small clarification, my statement "we do keep both dilute sulfuric acid and dilute nitric acid in the teaching labs here" in no way implied that it's used for cleaning glassware or that we let the undergrads just randomly play with strong acid. (+)H₃N-Protein\Chemist-CO₂(-) 02:19, 19 February 2013 (UTC)

But there are some professionals who specifically specify fuming nitric acid though[13], hence my question. In any case, thanks for all the responses, guys. It's been a real eye opener. Dncsky (talk) 04:44, 19 February 2013 (UTC)

Resolved

If 'you' know what effect that RFNA has on baked-on encrusted carbonated glassware then fine. I'm just saying that for those folks that can obtain access to these chemicals – they should not try it at home – especially, if they live next door to me and if they don't know the A to W to archive the right dilution. De-rusting the gas tank on your classic car with nitric.... forget it … a little knowledge can be a dangerous thing. “Hi Aspro, can you be right neighbourly and lend me some of you battery top up acid? My son's following this recipe where he boils up some cotton wool in nitric and now he need a little sulphuric... I'll tell you this, that 'ol tree stump in the back yard will be out the ground tomorrow – just you wait and see.” So just saying.--Aspro (talk) 15:31, 19 February 2013 (UTC)

The original question was about suggestions offered by an "Organic Laboratory Techniques" handbook for cleaning specialized scientific glassware in a laboratory setting. I don't think anyone was suggesting that this was general wisdom for cleaning everyday household items. (+)H₃N-Protein\Chemist-CO₂(-) 14:36, 20 February 2013 (UTC)

Arthur C Clarke Space Elevator

Hi, I read the quote from Arthur C Clarke again today about the space elevator being built "50 years after everyone stops laughing". What did he mean by this? Did he just mean 50 years after everyone starts taking the idea seriously, or is there something more I'm missing? I'm sure its really obvious but my brain is slow today... 80.254.147.164 (talk) 16:55, 18 February 2013 (UTC)

I think your 1st instinct was right. That is, it will take some 50 years of development to make it work, and that can't start until the idea is taken seriously. StuRat (talk) 16:58, 18 February 2013 (UTC)

NASA started spending money on space elevators in 1995. So we can be fairly sure that at least those people had stopped laughing. So we're about 40% of the way into Arthur Clarke's 50 years. That would put the space elevator completion date around 2045. I don't think any of the developers believe that's possible. However, Clarke left himself a loophole - he said "50 years after everyone stops laughing" - I'm pretty sure there will still be laughing right up the the first day it actually works!

Sadly though - it's looking like he may not be correct. I think enough people have taken the idea seriously - and between the tremendous difficulties with making a sufficiently light/strong tether - and the much more problematic issues of stability - he may have been wrong about whether it'll ever be built. However, there are lots of people working on various aspects of the problem - and a good amount of research money is going into solving these problems - so nothing is certain.

SteveBaker (talk) 20:32, 18 February 2013 (UTC)

Well, even if the version he had in mind, only supported at the top and bottom, doesn't work, you could always have one which is powered and has upward propulsion at various points along it. StuRat (talk) 21:57, 18 February 2013 (UTC)

No-one questions that (given sufficiently strong materials) it would work once erected: the difficulties lie in the erection and the dangers of failures during that process. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 13:57, 19 February 2013 (UTC)

No, no, no. That is absolutely not the case! There are severe concerns about the stability of the cable due to things like Coriolis effect forces on the elevators. These things start the cable swaying - and damping out that motion is difficult with the vast majority of the system being above the atmosphere and extremely flexible. As StuRat points out, you might be able to put rocket motors at intervals along the cable to counter this motion - but then the system needs power and fuel and all sorts of other things that make the whole concept much more difficult. There have been suggestions that you could cancel out these forces by running the elevator very slowly (like 2 months to get from bottom to top) - or by having multiple elevators climbing the cable at the same time (which makes the strength requirements of the cable vastly bigger - and means that you can't bring the elevators back down again once they're up there).

Then there are issues of how to handle wear on the cable and small breakages due to flaws in the materials. Those are exceedingly hard to repair on-the-fly.

With our present level of knowledge, the space elevator is far from a "do-able" problem - even if the cable strength issues can be resolved using something exotic like carbon nanotubes.

SteveBaker (talk) 14:29, 19 February 2013 (UTC)

For a single robot crawler, a single cable should suffice, but as loads increase, its really just a matter of designing a larger structure to handle these. --Modocc (talk) 17:06, 19 February 2013 (UTC)

But that's just not true. The technology doesn't scale at all well. SteveBaker (talk) 20:50, 19 February 2013 (UTC)

The current technology doesn't scale, for the material needed is not even here yet. Strength-weight ratios might improve dramatically though with better models and fiber design. Once we have made one cable that works well, more will be made and used in new designs that do scale. -Modocc (talk) 00:05, 20 February 2013 (UTC)

I would hate to be on such an elevator when an asteroid or meteor came along and severed it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:36, 19 February 2013 (UTC)

If that catastrophe were to happen, I'd make sure one could fly away! :) I imagine too that a large spiraling suspension bridge type construction would work, because each counter-weighted (the weights are in orbit, which can be bundled with a large structure, like with marionette control bars) cable would need to support only a very small portion of the road (or tracks). The structure can have lanes for both directions of travel and the suspension cables would be isolated from the vehicles. The vehicles which are capable of traversing this bridge could also be wheeled like when one climbs up and down a mountain with an auto. With a large enough structure, the incline can be gradual, but with a shorter near vertical incline, a coilgun type system should get you to orbit and back. At some point, if we ever are able to manufacture cables that are strong enough, it could become commonplace to be taking out one's favorite retrofitted computer driven auto to an upscale establishment. Modocc (talk) 16:12, 19 February 2013 (UTC)

That at least isn't a problem! These machines are unlikely to ever carry people. The elevator would travel through the atmosphere quite slowly and that would expose people to huge amounts of dangerous radiation as it passes through the Van Allen belt. Astronauts only survive this right now because the spacecraft are moving really fast and don't hang around in the dangerous areas for very long. The power requirements for the elevator and the nature of a friction grip on a valuable, highly stressed cable means that the elevator will rise very slowly. They'd spend hours to days of travel through Van-Allen belts - and that would fry the astronaut without many tons of lead shielding - which kills the performance of the machine and makes for impossibly strong cables. The space elevator would have to be a cargo-carrier only. But the probability of an meteor/asteroid/comet hitting the cable is utterly negligable - there are much larger concerns here. For example, an earthquake or tsunami (for example) would induce dangerous waves along the cable. Lightning strikes on a wet cable in the rain would be a serious risk also - so it's likely that the base station will have to be mounted on a ship and moved around to avoid storms...which brings a whole other cluster of issues. SteveBaker (talk) 20:50, 19 February 2013 (UTC)

"...friction grip on a valuable, highly stressed cable..."???? You apparently didn't comprehend my design method. The bridge spans put a static downward load on the many cables which are numerous (essentially as many as are needed). The vehicles have no contact with the cables and therefore no friction. There are reaction forces, but their effects will depend on the bridge's resistance to these and other environmental loads due to its inertial mass which, as a mass, will be considerable. The bridge is suspended and anchors need not be inelastic, thus probably earthquake resistant. Storms might be a factor... again it depends on the mass and plenty of bridges weather storms (and floods), but the whole thing doesn't have to (although it probably will) extend all the way to the ground and/or it could have a few light-weight tethers to the ground to give it lateral stability. Depending on the orbit one wants to achieve it could take hours perhaps, and far less if a rail system is used, thus shielding (we will need some substantial shielding anyway, something the astronauts could not afford much of due to mass restrictions) may or may not be much of a factor. -Modocc (talk) 21:46, 19 February 2013 (UTC)

Respondents here have clearly read the PR blurb and missed the math. Read this: http://www.sciencedirect.com/science/article/pii/S009457650800338X - it's not saying that the elevator is impossible, but very likely so inefficient that it won't ever be economically viable.

SteveBaker (talk) 20:50, 19 February 2013 (UTC)

Very first sentence: "The space elevator offers an alternate and efficient method for space travel." Its unstated conclusions are behind a paywall, but why bother? -Modocc (talk) 21:46, 19 February 2013 (UTC)

I can access the whole article, and its conclusion is almost the exact opposite of what you claim. Quotes:

"The effect of climber transit on the base of the space elevator is negligible..."

"However, due to the relatively small mass of the climber and the fact that the ribbon itself is not actually deployed or retrieved, the decay or growth of the oscillatory terms is small. This result distinguishes the dynamics of the space elevator from those of a typical tethered satellite system, where the growth of tether oscillations during constant rate retrieval can be very large."

"Since both of these values have upper bounds, the ribbon libration they cause is bounded as well; it will be of the order of milliradians at most."

"Still, the ribbon will experience undamped oscillations about its vertical equilibrium position. The period of such oscillations would be about five to six days. Even though the amplitude of these oscillations is small, it is desirable to minimize, and if possible, eliminate it."

"Three simple climbing procedures that aim to minimize or eliminate residual oscillation upon climber arrival have been presented [...] The second climbing procedure aims to eliminate ribbon oscillations. It is applicable for the case where a single climber is sent from one point on the ribbon to another at a constant speed. If the climber is sent at the moment when the ribbon reaches its maximum eastward propagation with a specific climber mass and velocity pairing, the ribbon will reach equilibrium at the moment when the climber arrives at its destination; the oscillation can be eliminated by using the Coriolis force on the climber." --140.180.243.51 (talk) 00:03, 20 February 2013 (UTC)

Completely fictional, but Kim Stanley Robinson described the fate of a space elevator that was severed at anchor point (in space) in Red Mars as mentioned above by Baseball Bugs. I've never liked the idea in the first place, but Robinson's description of the thing crashing down was enough to convince me that—feasibility and other subjects touched upon above aside—this is one of the most frightening ideas we've ever come up with as a race. Which means it'll probably happen several centuries from now, at some point in the far future when celebrities own their own moons. – Kerαunoςcopia^◁_galaxies 22:45, 19 February 2013 (UTC)

Personally, I found the concept in SimCity 2000 of a microwave energy satellite going off-track far more disturbing. Entertaining in a game, though. — The Hand That Feeds You:^Bite

As you said, that description is entirely fictional. Since any plausible material for a space elevator will be lightweight, the cable's terminal velocity will be very low. It might (or might not) be enough to kill a person with a direct hit, but there's no risk of damage to buildings or trees. --140.180.243.51 (talk) 00:03, 20 February 2013 (UTC)

If we did manage to make a space elevator we'd make it big not small, something capable of lifting hundreds if not thousands or tens of thousands of tons at a time and the cable might be many yards across. If it was snapped it certainly would cause damage. Probably you'd want shelters at the bottom just in case and have it some distance from anything else. Dmcq (talk) 17:31, 20 February 2013 (UTC)

Current designs call for a ribbon rather than a cable. In the event that it breaks at the upper end, most of the ribbon will burn up on re-entry, and the bits that don't will have the terminal velocity of a sheet of paper. --Carnildo (talk) 23:22, 21 February 2013 (UTC)

Tons of metal falling down will case damage. Dmcq (talk) 11:55, 22 February 2013 (UTC)

Salticid eyes

Hello,

what colors do the retina layers of salticids recognize? Is it blue, red or green or how is it constructed?

Greetings HeliosX (talk) 19:35, 18 February 2013 (UTC)

From the Wikipedia article on Jumping spider, it says that those types of spiders have tetrachromatic vision and are sensitive to UV light. Their retina presumably can detect up to four colors. See Tetrachromacy. 140.254.121.36 (talk) 19:52, 18 February 2013 (UTC)

Also enjoy this nice book article "How jumping spiders see the world", here on google books [14]. Of note is that they have a "staircase" retina, which they move to focus, rather than their lenses! SemanticMantis (talk) 20:17, 18 February 2013 (UTC)

They also have one of the most robust visual cognition systems of all invertebrates; with certain species like the domestic jumping spider in particular, you can note that they will track the movement of a large entity like a human (and even individual body parts thereof) with much finer attention than the overwhelming number of critters their size. To the OP, this article describes the specific frequencies of light which the photoreceptors of the retinas are sensitive to, with regard to two specific species. Snow (talk) 07:34, 19 February 2013 (UTC)

Identify guinea fowl-like bird with white cheeks and orange wattles

My nephews and I went out to feed the geese in the US North East this weekend in freezing weather. We found instead what I think of a standard guinea fowl with coal-colored feathers with small white spots. But they had bright white cheeks, yellow beaks, and a small bright orange wattle along what would be the jawline on a human on each side. Can anyone suggest what species these might be or what variety of what species? Google image searches get me things that look like the same genus but not identical. Thanks. μηδείς (talk) 20:37, 18 February 2013 (UTC)

Could it be Helmeted Guineafowl? 140.254.121.36 (talk) 20:55, 18 February 2013 (UTC)

(EC) There is a a lot of variety in guinea fowl. Some of them have white cheeks, yellow beaks, and orange wattles. I think there must be some plasticity in the color of the cheeks and wattles, even within species (think overall health and diet). Anyway, check out the helmeted guineafowl. Our article shows one with bluish cheeks, but this zoo page shows [15] theirs with white cheeks. Is that close at all? SemanticMantis (talk) 20:58, 18 February 2013 (UTC)

Related: does anyone have refs of feral GF flocks in the NE USA? I had not heard of that before... SemanticMantis (talk) 21:00, 18 February 2013 (UTC)

Common Birds of the New England Area — Preceding unsigned comment added by 140.254.121.36 (talk) 21:09, 18 February 2013 (UTC)

First, I am absolutely certain they are Guinea Fowl, which aren't native to the US. Second, while they do look like helmeted guinea fowl from the neck down, they have bright yellow beaks, no wattles at the nares or above the "jawline", and bright orange ones at that, and bright white cheeks--they could be Crayola Crayon standard colors or the focal colors of Berlin and Kay. Third, they have absolutely no helmet or crest whatsoever--even though in body shape and the color and pattern of the plumage they are identical to standard helmeted guineas, and their beaks seemed a bit less robust. There were six individuals, and they were identical, no apparent sexual or age variation, so I am wondering if perhaps they were hens or juveniles or juvenile hens. Their white heads were closer to the Pearl variety, but still no crests and their wattles were smaller than and less forward pointing, basically only the size of the white are of the wattles on this Pearl specimen, as if the white part were orange and the red part snipped off. Pearl. μηδείς (talk) 01:57, 19 February 2013 (UTC)

Standard components in Edison, Tesla, and Marconi's day

Where'd they go to get, say, a resistor of X ohms, a capacitor of Y microfarads, or an inductor of Z henries when implementing one of their designs? Not Radio Shack or Mouser, I presume :) 67.163.109.173 (talk) 22:48, 18 February 2013 (UTC)

Edison had his own staff, and I imagine the others did, too, or made the items themselves. StuRat (talk) 23:01, 18 February 2013 (UTC)

I wold like to know (for knowledge's sake, not that I would expect to be able to do it in my garage) if records/documentation for their "recipes" and construction methods/procedures to construct components with specified component values have been preserved. 67.163.109.173 (talk) 23:06, 18 February 2013 (UTC)

Michael Faraday's Experimental Researches... contains many experimental descriptions that are very cook-book-recipe-like. By the era of Edison and Marconi, electrical components were already commercially available. For example, Federal Telegraph Company is famous in these parts; they used to sell great big ferrite cores and integrated radio systems, dating back to the very early era of radio. Telegraph and telephone companies, like Western Union and Bell and AT&T (the original corporation) were already building large scale telecommunications systems, and they manufactured support electronics on industrial scales. Nimur (talk) 23:48, 18 February 2013 (UTC)

Thanks. Related to first precision components, I always wondered; the first calibration measurement devices to be able to measure to a given precision, how were they calibrated, given that prior to them, one could not know that their components were accurate to that given precision. For example, the first capacitors asserted to be accurate to within 10 microfarads, the tester used on them would need to be able to measure within 10 microfarads to know what value they were. So the device to test the first capacitor with a value within 10 microfarads of its nominal value needs to be able to do whatever it does to indicate "yes" within 10 microfarads of that value. Doesn't that device need such level precision capacitors in it? But prior to this moment, no such precision capacitor has been made (knowably with any degree of confidence). This questioning could go for resistors or inductors, I suppose, not just capacitors, which I used as an example. 67.163.109.173 (talk) 00:29, 19 February 2013 (UTC)

Well, for simpler measurements, like length, they just carved a line in stone somewhere, declared that to be a foot, and measured everything else against that. I suppose a similar method could have been used with more complex measurement devices. StuRat (talk) 01:50, 19 February 2013 (UTC)

I am an electrical engineer by occupation, and electronic engineer by qualifications and hobby, and have been involved in a bit of chemistry. The great thing about electrics and electronics is that it is quite simple and easy, if a pretty bit tedious, to home-make basic components because they are calculable, and you can build up from there. For instance, given the physical dimensions, the capacitance of an air-spaced capacitor can be calculated with a high degree of precision (> 4 place accuracy is not at all difficult with a modicum of enginuity). The inductance of a toroidally wound air core inductance can also be calculated from its physical dimensions with a high degree of precision. I wish chemistry was like this!

In a home electronics lab, all you really need is an accurate DC voltmeter, and accurate frequency meter (both easy to get without much expense: 5-digit digital voltmeter ~ $200, 6-digit frequency meter about the same), and an accurate capacitor (home-made), and you can construct apparatus to relate all measurements back to these, for calibration purposes. 100 years ago, labs used the Weston Cell as an accurate voltage for calibration purposes. Oscillators were compared with others by counting beats and ultimately referred back to a mechanical clock, whose accuracy was assured by comparison with observations at astronomical observatories.

Ratbone 60.230.235.171 (talk) 02:39, 19 February 2013 (UTC)

Standards might be determined in world-class physics labs, such as the work of Maxwell and Thompson in the 1860's [16] with standard cells and carefully managed galvanometers, or Lord Rayleigh and (his faithful companion Mrs. Sidgwick) to define a column of mercury of some length of some cross section at some temperature as having a specified resistance. See [17]. They followed on the heels of Davy, Faraday and others. The telegraph industry made use of standards and measuring instruments by the 1850's, to achieve commercial success. A useful and practical lab standard resistance could be made with a certain length of resistance wire, such that it has a desired resistance with a stated precision at a stated temperature, and correction factors could be applied for other temperatures. Lab supply houses could make and sell to experimenters such standards. Bridge circuits could be used with standard voltage cells, standard resistances, inductances or capacitances to measure or adjust other secondary standards. An early 20th century or late 19th century electrical lab had big, expensive and delicate instruments for precision measurements, museum pieces today, just to achieve similar precision to a digital meter today costing a few hundred dollars.Edison by the 1870's could buy or have whatever measurement devices he needed. Tesla in the 1890's could just write Westinghouse and have motors or generators built for his lab, or could have his workmen build new devices. Experimenters did not always need state of the art accuracy in measurements, compared to the physics labs developing standards with many digits of accuracy. Edison (talk) 16:58, 19 February 2013 (UTC)

freezing point of water

Would a solution with 250 ml of rock salt and 25 ml water 125 ml ice have a much lower freezing point than a solution with 175 ml of rock salt, and 25 ml water 200 ml ice? At the beginning of my experiment, the 400 ml beaker was half full with ice, and the rest was rock salt (with a tiny bit of rock salt). Alot of rock salt was added to the beaker, over the course of the experiment. — Preceding unsigned comment added by 99.146.124.35 (talk) 23:29, 18 February 2013 (UTC)

Does our freezing-point depression article help? Mikenorton (talk) 23:37, 18 February 2013 (UTC)

If the extra rock salt dramatically lowers the freezing point of the ice in the 400 ml beaker, how would that impact the freezing point depression constant of the fluid inside the vial that is positioned inside the 400 ml beaker? All of the freezing point depression constant Kf values of the water that was mixed with citric acid inside the vial were much lower than what they should be (0.5 and 0.65 is what they came out to be. — Preceding unsigned comment added by 99.146.124.35 (talk) 23:41, 18 February 2013 (UTC)

Citric acid ? As for the effect of more rock salt, there's only so much salt that can be dissolved in the (liquid) water. Beyond that, more won't change it's properties, it will just sit on the bottom. However, rock salt has lots of other junk in it, some of which might be dissolved by water and affect it's properties. In a chemistry experiment, I expect you'd want to use pure table salt (non-iodized sodium chloride). StuRat (talk) 02:35, 19 February 2013 (UTC)

If you want to REALLY lower the freezing point of water, you can make a saturated solution of calcium chloride and see how cold you can get it without freezing it.  :-) 24.23.196.85 (talk) 05:01, 19 February 2013 (UTC)

Rock salt will lower the freezing point of water by maximum −21.12 °C for saturated solution with 23.31 wt% of NaCl. See also [18]. Ruslik_Zero 07:54, 19 February 2013 (UTC)

February 19

contracting rabies

I have looked extensively for information that would tell me if deer or elk can contract rabies. I have never heard of these animals becoming infected and would like to know if it is possible and/or how common.98.22.220.148 (talk) 01:40, 19 February 2013 (UTC)

Yes deer can get rabies, e.g. [19][20], though rabies is rather rare for deer. Based on the first link, of the 7000 rabid animals found in the United States each year, about 5 will be deer in the typical year. Dragons flight (talk) 02:04, 19 February 2013 (UTC)

Thank you!98.22.220.148 (talk) 02:47, 19 February 2013 (UTC)

All mammals can get rabies, apparently birds also but I don't know if that's ever been found in the wild. A factor which limits finding rabid animals is their survival of the infective event; for instance, small mammals like mice and rabbits aren't found infected, apparently because they rarely or never survive the attack by an infected animal. In a similar vein, deer or elk are unlikely to survive an attack by an infected large carnivore like a cougar, wolf, or even a large dog; but also are unlikely to be successfully attacked by something small like a rabid fox or raccoon so wouldn't get infected in an attack they could survive. Just my opinion. Gzuckier (talk) 19:53, 19 February 2013 (UTC)

Double-slit experiment and scale

When performed on subatomic "particles", like electrons and photons, I understand that the resulting interference pattern associated with waves is produced. When performed with much larger objects, like bullets, no interference pattern is observed. So, my question is, at what scale does the transition from wave behavior to particle behavior occur, and how does it occur ? Is there a gradual change from one to the other, or an instant change ? We could try larger subatomic "particles", like protons and neutrons, small atoms, large atoms, small molecules, large molecules, etc., until we get to the size of a bullet. StuRat (talk) 04:00, 19 February 2013 (UTC)

By theory, ALL well-defined objects should be subject to wave-like properties, per the de Broglie relations; it's really an engineering problem and not a science problem; that is, even for bullets, there should be an associated wavelength which could be calculated given the mass and velocity of the bullet; knowing that wavelength would give you the way to construct a set of slits through which the double-slit experiment should be valid, the issue is in the actual construction of them, which may be a physical impossibility due to the restraints imposed by using real materials in the experiment, but again this is an engineering issue, not one in the theory. In actual experimentation (according to information at the Matter wave article), the largest particles shown to diffract experimentally (and thus display real wave-like characteristics) have a mass just shy of 7,000 atomic mass units, which would be about the size of a smallish protein molecule (for comparison, hemoglobin has a mass of about 64,000 amu.) --Jayron32 04:56, 19 February 2013 (UTC)

And, at that scale, do we get a pure interference pattern, like a wave ? StuRat (talk) 05:01, 19 February 2013 (UTC)

Again, there are no theoretical limits here, just engineering limits. You can calculate all the parameters; the size and distance between the slits, the parameters of the interference pattern you get, for any arbitrary object, from an electron up to, say, a star. The parameters work to infinity in all directions; there is no hard limit where any well defined object stops following quantum behavior. Instead, there's a limit where the difference between quantum behavior and classical behavior becomes smaller than tolerances of our measuring devices, or where the actual means to construct, say, two slits to diffract bullets becomes a physical impossibility. But the math should work, and we have no reason to suspect that it would be wrong per se, just that the actual construction of an apparatus to test it would be impossible. --Jayron32 05:25, 19 February 2013 (UTC)

(edit conflict) Someone should check my math, but I just did the calculation of a 20 gram bullet (0.020 kg) fired at a speed of 1000 m/s, and came up with a de Broglie wavelength of 1.91 x 10^-40 m. For comparison, the charge radius of a proton is 8.75 x 10^-16m, which means that you could fit about 200,000,000,000,000,000,000,000 or so de Broglie wavelengths of the bullet within the radius of a proton. If you can create slits small enough and close enough to run a double-slit experiment on something like that, you're a better man that I. --Jayron32 05:43, 19 February 2013 (UTC)

Clearly a bullet wouldn't fit through those slits. Does that mean there's a hard limit where the particle is larger than the required slit ? StuRat (talk) 05:49, 19 February 2013 (UTC)

It also depends on velocity; I believe (and I may be wrong on this assumption) that objects moving closer to the speed of light could fit through smaller slits, due to relativistic effects on their dimensions. So, depending on how fast you can get your bullet moving, you could get it to squeeze through any arbitrarily sized slit. Practically, of course, you are correct, eventually, your object size and your slit size are moving in opposite directions, and you reach a limit where the slits become too small to fit the object in question through, at which point the experiment becomes impossible. See below, where I found the results of an experiment where the slits were only about 500 times larger than the diameter of the object, which is still pretty close in size. --Jayron32 06:12, 19 February 2013 (UTC)

I don't think so. Relativistic length contraction will only apply to the axis along which the object is moving. Your relativistic bullet would be just as wide as before, but shorter. You'd also run into the issue of higher speeds producing ever shorter wavelengths. Someguy1221 (talk) 06:21, 19 February 2013 (UTC)

Like I said, I wasn't too confident on that part. So, there would be a real physical limit, which is where the shrinking slit size and the growing object size pass. --Jayron32 06:31, 19 February 2013 (UTC)

There are ways to "cheat". The simplest demonstration is to have slits that are much narrower than the object's wavelength, but weaker effects can allow one to demonstrate interference and other quantum effects even if that isn't the case. However, in that scenario one needs to do the analysis of the situation more carefully and the measurements are generally harder. In the C₆₀ molecule interference demonstration, the C₆₀ have a diameter of about 1 nm and passed through slits ~50 nm wide with a 100 nm separation. However, in this case, the de Broglie wavelength is only about 2.5 pm (i.e. 0.0025 nm). In other words the slits were already orders of magnitude larger than the de Broglie wavelength, so the waves would only be very weakly diffracted, but the quantum effect was still large enough to measure. (In this case "large enough to measure" meant diffraction peaks separated by about 20 microns.) Dragons flight (talk) 06:33, 19 February 2013 (UTC)

There are theoretical limits. First, the wavelength you calculated is smaller than the Planck length, so it probably doesn't make sense to talk about it without a theory of quantum gravity. Second, unless they're cooled to near absolute zero, bullets emit blackbody radiation which leads to environmental decoherence within a much shorter time than you'd need for the experiment. Third, even if you do this at very low temperature, bullets have a lot of internal state (they're malleable, for example), which would likely record which-path (welcher-Weg) information, which destroys the interference pattern. Any one of these alone makes the experiment impossible. -- BenRG (talk) 08:26, 19 February 2013 (UTC)

And I'm also interested in the reverse Q: What's the smallest object which can be fired thru the double slits, without a detector to show which slit, that still doesn't exhibit an interference pattern ? StuRat (talk) 05:37, 19 February 2013 (UTC)

I'm not really good with the optics calculations, but roughly speaking the more massive the object, the smaller its de Broglie wavelength is, so the smaller and closer you'd have to make the slits in a viable double-slit experiment. So, what you would need to do is calculate the relationship between slit size and wavelength, and then figure out what the smallest slits you can make are, and then use the de Broglie wavelength equation to calculate what mass corresponds to whatever wavelength you can diffract with the smallest slits possible to make. That would be the practical upper limit for an object you could successfully run a double slit experiment on. --Jayron32 05:47, 19 February 2013 (UTC)

Just for an example of a good double-slit experiment using massive particles, here is the results of such an experiment run on Buckminsterfullerene molecules (C₆₀, mass = 720.64 amu) which showed interference patterns consistent with theoretical predictions based on calculated de Broglie wavelengths. The slit sizes here are really freaking small: it required 50 nanometer slits spaced 100 nm apart. The diameter of one of these molecules is about 10.18 Å (according to https://sesres.com/PhysicalProperties.asp), which means that the slits are about 500 times larger than the molecules themselves. At some point, you'd reach the point where the slits become smaller than the diameter of the particles; this may (or may not) represent some sort of physical limit. I think you can count on relativistic effects to allow for an object larger than the slit to pass through it (that is, by firing the object at some speed very close to the speed of light, you can still get it to pass through a slit which is smaller than it is, when the slit and the object are at rest relative to each other), but we're getting out of the realm where I'm capable of doing such calculations, or even discussing it confidently in broad terms. --Jayron32 06:06, 19 February 2013 (UTC)

I don't see how you could use length contraction to get an object through a narrow slit, given that only lengths in the direction of motion are contracted. -- BenRG (talk) 08:26, 19 February 2013 (UTC)

Yeah, like I had already said above, I was wrong about that. I'm still wrong about that. --Jayron32 13:32, 19 February 2013 (UTC)

Oops, sorry I missed that. -- BenRG (talk) 06:48, 21 February 2013 (UTC)

Small correction: 10 Angstrom = 1 nm, so it's 50 times larger, rather than 500 times larger. -- 205.175.124.30 (talk) 22:19, 19 February 2013 (UTC)

Imaging C60 in double-slit experiment

This post has reminded me of something I meant to ask.

Given that buckminsterfullerene has a diameter of 1 nm, each molecule can be imaged with e/m radiation of over 300PHz, which is soft x-rays and up. Is it possible to use a hard X-ray camera pointed in the same direction as the slits, (normal to the direction of the C60), and then fire individual C60 molecules in the experiment, to track each molecule? Or does this violate wave/particle duality? CS Miller (talk) 20:49, 19 February 2013 (UTC)

Presumably, just like other attempts to tell which slit they use, if successful, this would destroy the interference pattern, and you'd see the simple sum of particles passing through both slits, at the detectors, instead. As for how it can do this, we have to imagine that the x-rays in some way disturb the particles. StuRat (talk) 22:00, 19 February 2013 (UTC)

For the second part of your answer, you are probably right StuRat, a 3,000PHz photon has 2 fJ of energy, enough to accelerate a 60*12 amu object to 57.7 km/s; unless the molecule can complete the experiment in a few microseconds, it will probably be forced onto the far end of the container.

For the first part, if the camera was far enough away for the photos to reach it, after the molecules hit their detector, then the observation can't affect the interference pattern. (I think, I'm not strong on quantum mechanics). CS Miller (talk) 23:18, 19 February 2013 (UTC)

It will affect the interference pattern, because the photons carry information about the particle path just as much as the photographic film later will. Regardless, I don't think you can make a shadowgraph of nanometer-scale particles using x-rays. -- BenRG (talk) 06:48, 21 February 2013 (UTC)

wireless electricity transmission

please give me the details that how it possible to transmit electricity without wires(wireless)? what are the recent researches in this field? as well as what is the future of this?? — Preceding unsigned comment added by 49.50.96.200 (talk) 08:11, 19 February 2013 (UTC)

The wireless power article would be a good place to start. -- BenRG (talk) 08:15, 19 February 2013 (UTC)

Transmitting small amount of electricity wirelessly over small distances is easy, you can use things like electromagnetic fields to convey power a few inches. Transmitting large amounts of electricity wirelessly a long distance is more problematic. Tesla wanted to do it with radio waves, but this is quite dangerous, inefficient, and it's difficult to do billing (current radio and broadcast/satellite TV does transmit a tiny amount of electricity wirelessly, but needs electricity from wires to amplify the signal (with the exception of a crystal radio). You could also point a laser at a distant solar cell, and transmit electricity that way, but this would be inefficient and require a clear line-of-sight. StuRat (talk) 09:39, 19 February 2013 (UTC)

Talking of fields, this video shows transmission in a field.[21] Unfortunately, the camera used is not sensitive enough to actually convey how amazing this is when demonstrating it to the doubting Thomas's and grandchildren. When your eyes become light adapted to the darkness the tubes are bright enough to read by. If a factory or office near you is replacing its tubes, the old ones can be picked up for a few cents each. I'm surprised that this demo didn’t use balancing coils to enhance the power -(as the tube are only four to six feet long).--Aspro (talk) 15:55, 19 February 2013 (UTC)

Back in the dawn of time when I used to subscribe to Popular Electronics, they had a project that was a crystal radio with a one transistor amplifier stage, which was powered by another crystal radio which was tuned to a powerful local station. Never built one, but how cool is that? Gzuckier (talk) 19:58, 19 February 2013 (UTC)

Not very cool at all actually. Other electronics magazines reckoned it would not work. So I decided to investigate. Well, it would work in theory. Trouble is, you need to produce a voltage exceeding the saturation voltage of the transistor (V_CEsat) and a few 10's of microamps for it to work. With the most suitable germanium transistors of the day, that's about 100 mV into 2000 ohm or so. With a realistically sized long wire antenna, you need to be within visual range of the power source transmitter to get that. And you need an earth connection, << 2000 ohm, as well I set up a long wire antenna in a park next door to a long wave navigation transmitter (2 kW), using a water pipe as earth and could not get enough for the transitor to amplify. Ratbone 121.221.37.9 (talk) 03:05, 20 February 2013 (UTC)

Nice way to force the big guys to support the little guys. Now if we can just get Microsoft to support Linux. :-) StuRat (talk) 20:05, 19 February 2013 (UTC)

In the 1980's Microsoft sold Xenix - their version of UNIX that would run on a PC. My employer at the time had databases running on it. It was ok to use & maintain, if lacking in features. It was a utter market failure and Microsoft sold it off to SCO who marketed it as SCO Unix. I have it, at employer's expense, on one of my home computers for training/experience purposes, but seeing as the vastly better and more common Sun Microsystems UNIX o/s with your choice of GUI is free for home use, I don't know why anyone else would bother. Ratbone 121.221.37.9 (talk) 03:14, 20 February 2013 (UTC)

See Space-based solar power as one possibility. Note that this isn't directly "electricity" being transmitted, rather solar power being transmitted as a microwave signal to the ground, which then converts to usable electricity. — The Hand That Feeds You:^Bite 23:24, 19 February 2013 (UTC)

Classification of animals

In here (page 95) the classification of animals is shown. I'm having trouble understanding how animals with tissue level of organisation are further divided. Can anybody please explain? Thanks. --Yashowardhani (talk) 10:30, 19 February 2013 (UTC)

Our body cavity article explains this pretty clearly -- see the section called Grouping. If you need more information, please follow up. Looie496 (talk) 16:21, 19 February 2013 (UTC)

Thank you so much, the article helped a lot. Could you please also explain how coelomates are further divided? --Yashowardhani (talk) 11:22, 20 February 2013 (UTC)

Is it possible to discharge electricity by alternating current (AC)?

In discharge tube, electric discharge takes place when we supply direct current (DC). If we supply AC instead of DC, will the electric discharge take place in the same way as in case of DC? 27.62.227.241 (talk) 11:17, 19 February 2013 (UTC)

Yes, however there is an important difference. With DC, there must be sufficient voltage to start the discharge, ytermed the striing voltage. Once the arc has started, a gnenerally very much lower voltage is required to kepp it going. With AC, unless the arc is quite large, as in arc welding, the will stop each time the voltage goes to zero, 100 times a second (120 times in USA and certain other countries). Hence with AC the peak voltage must be kept continuously above the strike voltage in order to keep the arc going. Keit 60.230.216.137 (talk) 12:28, 19 February 2013 (UTC)

Electric discharge in gases and arc lamp are two relevant articles. DMacks (talk) 16:30, 19 February 2013 (UTC)

One thing you should notice that, in discharge tube (DC) cathode and anode never exchange their position, on the other hand, AC is fluctuating. 27.62.227.241 (talk) 16:54, 19 February 2013 (UTC)

Biochemistry

is that right that Glucose and Phosphat (or phosphorous) are the main ATP sources (and thus, sources for short-time energy), while, Creatine and Fat are the main "long term energy" sources ?.

thanks.

All (or almost all) of the biological energy sources go through ATP. The question is how the body regulates the conversion. The process of glycolysis is the main energy generating pathway in heterotrophs, so typically glucose is thought of as a primary energy source. It's certainly the case that blood glucose, when available, is typically used as the preferred external energy source. In contrast, energy generation from fat (acetyl-CoA production by fatty acid degradation, which ultimately leads to ATP production through the citric acid cycle and oxidative phosphorylation) is more complex, so it typically reserved for long-term energy storage. Even then, a portion of the fat isn't used directly, but instead is used for gluconeogenesis to produce blood glucose. Fat, being more energy dense than carbohydrates, tends also to be better for long-term storage of energy, although things like glycogen are used for medium-term energy reserves. As to the other compounds, phosphate/phosphorus by itself is not an energy source. It's role in energy metabolism is to serve as a building block of things like ATP. Creatine per se isn't an energy source, at least anymore so than standard amino acids are. The reason it's mentioned is because of creatine phosphate, which, like ATP, is a high-energy phosphoester that can serve as a store of energy. It's not used as an energy donor itself, though, instead functioning as a "buffer" for ATP in places like muscles, regenerating ATP when ADP levels are high, and being created itself from ATP when ATP levels are high. But that's more of a short/medium-term storage rather than long-term storage. -- 205.175.124.30 (talk) 22:13, 19 February 2013 (UTC)

Maybe the OP means polyphosphate (a universal acidocalcisome component, not just in polyphosphate-accumulating organisms) which holds energy-rich bonds comparable to those in ATP. For review see [22] [23]. I'm actually not quite sure what overall percent of the cell energy budget it represents in typical organisms. Wnt (talk) 23:25, 19 February 2013 (UTC)

Pantoon?

what is pantoon — Preceding unsigned comment added by 210.212.95.98 (talk) 12:57, 19 February 2013 (UTC)

Do you mean pontoon? StuRat (talk) 15:58, 19 February 2013 (UTC)

Or pantaloon or Pantone or platoon?--Shantavira|^{feed me} 16:12, 19 February 2013 (UTC)

Or Panton, pantun, Penton or Panettone? Red Act (talk) 16:16, 19 February 2013 (UTC)

Or Phantoon... --Tardis (talk) 01:56, 21 February 2013 (UTC)

Can you please give this word as used in a sentence. Pantoon could refer to a boat which as StuRat points out is an alternative spelling. We need the context to take this further.--Aspro (talk) 16:10, 19 February 2013 (UTC)

• Could also be Pantone (a system for color management)? Looie496 (talk) 16:13, 19 February 2013 (UTC)

The OP has 4 entries in the last 3 1/2 years. So figure it will be at least autumn before he gets back to this question. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:43, 20 February 2013 (UTC)

How do you polish a copied key to make it work better?

I've noticed that duplicate keys made by automated machines have groove marks on the cut surfaces, transverse to the length of the key. I think the groove marks make a duplicate key difficult to insert into and pull out of the lock. Is there an easy way to polish way the groove marks without affecting the function of the key? --108.2.210.178 (talk) 13:29, 19 February 2013 (UTC)

I've always used 400-600 grit "flatting paper" (carborundum type sandpaper that is normally used wet esp. in the automotive bodywork industry.) It's hard enough to remove any superficial burrs but fine enough that it will take some hard work to actually alter the shape of the key. An emery board (used for manicures) also works well for the same reasons. 196.214.78.114 (talk) 14:03, 19 February 2013 (UTC)

Common "Pin tumbler locks" only depend on the height of the high spots and the depth of the low spots on the key. What makes the key harder to insert and remove is the grooves on the sloping parts. As you insert the key, the pins inside the lock have to slide up and down those slopes - so if they are rough, you'll find the key hard to insert and remove...AND you'll wear out the lock prematurely too.

Hence, so long as you don't reduce the height of the 'hills' or the depth of the 'valleys' of the key - you should be able to gently smooth off the slopes between them using a very fine emery paper or a polishing stone on a Dremel (or something similar) without affecting the ability of the key to open the lock. I would only do this on a duplicate key for which you still have the original!

SteveBaker (talk) 14:12, 19 February 2013 (UTC)

Rope walking

I have seen people walking on ropes taking a long stick in their hands. I know they use the stick to balance their body. How can we explain this in scientific terms? 27.62.227.241 (talk) 15:03, 19 February 2013 (UTC)

Our article on tightrope walking explains the basic mechanics -- the increased weight, coupled with the increased distance from center of mass, increases the moment of inertia which reduces the angular acceleration of the person. This slows the tipping process and gives the person time to correct. — Lomn 15:12, 19 February 2013 (UTC)

There's a similar counter-intuitive experiment you can do. Try balancing a ruler and then a yardstick (or meter stick) on your fingertips, vertically. You'd think the smaller one would be easier to balance, right ? Nope, you need to make much faster adjustments to keep it steady than the longer stick. StuRat (talk) 16:02, 19 February 2013 (UTC)

similarly, weight one ennd of a yard/meter stick and you'll find it's easier to balance vertically on a finget with the heavy end up in the air, than with the heavy end down at the finger end. Hey, that would be one heck of a field blood-alcohol test for cops to use, no? "Your honor, we could only slide the weight 6 inches down the meter stick before the defendant could no longer balance it, he was clearly inebriated?" Gzuckier (talk) 20:03, 19 February 2013 (UTC)

Phone signal disconnecting a mouse

Hi, this may seem like a question for the computing desk, but I am not interested in how to fix the problem, just the scientific reason behind what is happening - I don't even intend to fix it, it fascinates me so much I kind of like it...

My PC at home has a standard wired mouse connected via USB to the back off the PC. Every time I have my mobile phone on my desk, and recieve a call/text on it, the mouse "disconnects", the cursors won't move and the Windows "hardware disconnected" sound plays. I have observed this happening too many times for it to be a coincidence, and I actually have to sit far back from my PC if I want to use the mouse whilst on the phone. My question is why is this happening? Is it the phone signal inducing a current in the wire? The signal interfering with the infared sensor on the bottom?

To reiterate: nothing is particuarly special aboout the set up; it is a plastic cheap-ish mouse with a plastic coated wire connecting it via USB to the motherboard at the back. Again, nothing is special about my phone, and I have observed it happening with multiple phones (I am not sure about mice). Thanks! 80.254.147.164 (talk) 15:24, 19 February 2013 (UTC)

I have observed a "galloping sound" on my PC speakers when the cell phone is near the wires. So, I do believe it's picking up interference on the wires, in your case, too. I would hope that it would "reconnect" once the text is finished. Does it ? StuRat (talk) 16:08, 19 February 2013 (UTC)

Yes it does, I thought the "galooping" sound was due to the signal interfering with the magenets in the speakers? 80.254.147.164 (talk) 16:27, 19 February 2013 (UTC)

I did an experiment where I wrapped the speaker wires around the cell phone, then sent a text, and the galloping sound was much louder, despite the distance to the actual speakers being the same. StuRat (talk) 16:37, 19 February 2013 (UTC)

Clever, I might do the same with the wire on my mouse - see if I can get to happen away from the actual mouse but wrapped in its wire. I will report on my findings tommorow. YEAHH SCIENCE!!!! 80.254.147.164 (talk) 16:41, 19 February 2013 (UTC)

Cool, please let us know how it goes. StuRat (talk) 16:43, 19 February 2013 (UTC)

Sounds like Electromagnetic interference to me. The interesting question is whether it is the microcontroller inside the mouse or the USB host on the motherboard that is getting confused. Cand you try another mouse on that computer and/or another computer with that mouse? --Guy Macon (talk) 19:48, 19 February 2013 (UTC)

Yeah - it definitely sounds like electrical interference. I would suggest adding a ferrite bead to the mouse cord - but to be honest, it would be probably be both cheaper and easier to replace the mouse instead. You might also try changing the length of the cord - if it's acting as an antenna, that might fix it...but again, it's not an easy thing to do.

What's happening (probably) is that the mouse cord is acting like a radio antenna. The abrupt emission of radio waves from the phone to the cell tower acknowledging that it's there is evidently just the right frequency to be picked up by the USB cord and that's evidently enough to cause either the mouse or the PC to decide that something went horribly wrong. When you halve the distance between the antenna and the transmitter, you quadruple the amount of energy produced in the antenna. So when you consider that the phone signal has to be picked up by a cell tower several miles away - and when the mouse cable is just inches away, the power is going to be millions of times more than the cell tower sees. Moving the phone further from the USB cord would obviously be a good idea.

SteveBaker (talk) 20:26, 19 February 2013 (UTC)

determination of pesticides by QuEChERS method using LC-MS/MS

HI I WOULD LIKE TO KNOW WHETHER IT IS POSSIBLE TO USE CLOPYRALID AS THE INTERNAL STANDARD IN THE DETERMINATION OF TRYCLOPYR IN WHEAT GRAIN COMMODITY.WILL IT NOT ELUTE AT THE SAME TIME AS THE COMPOUND OF INTEREST OR COURSE ANY INTERFERENCES OF SOME SORT? — Preceding unsigned comment added by Tsbu (talk • contribs) 15:29, 19 February 2013 (UTC)

For reference, we have clopyralid, Triclopyr, Quechers and Elution. Rojomoke (talk) 18:56, 19 February 2013 (UTC)

I have too little experience to give you a good answer, but my impression is that it depends on the precise method used for the gas-liquid chromatography - what column, what gas, I think even the temperature program? The obvious thing to do is to make up three samples with either compound or both, and see what you get. Wnt (talk) 17:36, 20 February 2013 (UTC)

Polarized lens sunglasses

1) Is it true that, if you have two polarized lenses, arranged in series, so each photon passes thru both, and each lens blocks 50% of the light, that by varying the angle of rotation of one lens, so it's either in the same orientation as the stationary lens (both horizontally polarized or both vertically, for example), or at a 90° angle (so one is horizontal, and one is vertical, for example), you can vary the total blocking of light from 50% to 100% ? StuRat (talk) 16:16, 19 February 2013 (UTC)

Yes, or nearly a 100%. If the light is bright enough some light leaks through.--Aspro (talk) 16:18, 19 February 2013 (UTC)

Why is that ? Is it some flaw in the polarized lenses, or does light have the ability to change it's polarization from one lens to the other, or is it just that you can never quite get exactly 90° ? StuRat (talk) 16:23, 19 February 2013 (UTC)

Because attenuation is not a "binary," "completely on" or "completely off" effect. Polarized light incident on a differently-polarized medium is attenuated. If we analyze one single photon, we can say "one single photon has a probabilty P% of passing through the medium." And if we analyze a large ensemble of photons as a continuous incident light source, then we say "the polarizer attenuates the light to P% of its incident value." Nimur (talk) 16:28, 19 February 2013 (UTC)

OK, so if it's not 100% blockage, what percent can be achieved ? StuRat (talk) 16:35, 19 February 2013 (UTC)

That depends on the thickness of the glass and the sensitivity of your experiment. At some point, increasing the attenuation of "wrongly-polarized" light will also increase the attenuation of "correctly-polarized" light, and soon we have an opaque material. Are you asking for the optical properties of many common glass? My go-to reference, Applied Photographic Optics, has a full chapter on polarization, and another on attenuation, and has lots of details about commonly-used glass. We can easily build polarizers that attenuate 50% of all light and 95% of oppositely-polarized light. Sunglasses are probably in that ballpark. Nimur (talk) 16:43, 19 February 2013 (UTC)

So, then, my set-up would vary from 50% to 95% blockage, as well, depending on the angle of rotation ? StuRat (talk) 17:08, 19 February 2013 (UTC)

2) Does anyone make such a pair of sunglasses ? StuRat (talk) 16:16, 19 February 2013 (UTC)

Doubt it. We are talking rays not photons (which are packets of light energy). The medium used to filter light of one orientation only (were talking around 500 nano meters) have an angle of error and internal refraction. Hold two of the best polarization filters up to the sun and I reckon you will still see it. No 100%.--Aspro (talk) 16:36, 19 February 2013 (UTC)

P.S. Why are you asking? If you want to block out light competently why not use a thick bit of cardboard? Cornflake packets are cheap and readily available. A really low tech and practical solution. --Aspro (talk) 16:47, 19 February 2013 (UTC)

I'd like a pair which I can adjust. I'm aware of the ones which darken automatically in bright sunlight, but that fails in four respects:

A) They lag the light change, so, when driving under a bridge, everything can go black. I'd rather adjust my sunglasses going into a dark space, than have to take them off and put them back on. (Less chance of me poking myself in the eye this way.)

B) They don't adequately account for a single bright point of light ahead, like the old Airstream trailers (which should have been banned as a road hazard).

C) They don't account for my preference for light levels. Sometimes my eyes are bothering me and particularly photo-sensitive, so I'd like darker lenses. (Alcohol may be involved here.) :-)

D) At times I want to block more light to one eye than the other, right up to 100%. If I just had an eye drop in one eye, for example, which causes photosensitivity. (Yes, I could use an eye patch for this, but then I'd feel the need for a hook arm, peg leg, and parrot on my shoulder.) :-) StuRat (talk) 16:54, 19 February 2013 (UTC)

You don't strictly need any property of polarization, then; except to fine-tune the darkness. You can stack extra neutral density filters until the glass is as dark as you like, and use one rotatable crossed polarizer for fine adjustment. Nimur (talk) 17:08, 19 February 2013 (UTC)

Yes, but keep in mind that I don't want the minimum to go too high, either. For example, I wouldn't want sunglasses that can be adjusted to block between 90-99% of the light, as 90% might well be too much, in some cases. Of course, I could take them off, but then it might be too bright. Ideally they would be fully adjustable from 0% to 100%, but I don't think that's possible in something light enough for sunglasses, at present. Perhaps sunglasses with very tiny LCDs could do that, but this would increase the complexity and weight. StuRat (talk) 17:17, 19 February 2013 (UTC)

If it's any help, one can (or could) buy a similar arrangement for SLR cameras with one polarized filter rotating on another which is screwed to the front of the camera lens. A competent handyman could build a pair of these double adjustable filters into a spectacles frame. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 18:07, 19 February 2013 (UTC)

Cool, have any links ? StuRat (talk) 18:48, 19 February 2013 (UTC)

Here's a page of them from an online catalogue (click the less-than-obvious 'Learn more' links in the descriptions for further details). {The poster formerly known as 87.81.230.195 212.95.237.92 (talk) 14:04, 20 February 2013 (UTC)

Yikes, looks like the required 4 would cost me about 100 pounds. Any for 100 yen ? StuRat (talk) 05:29, 21 February 2013 (UTC)

could probably cobble something together from a couple pairs of the polarized variety of 3D glasses filched from the local showing of whatever is being foisted upon the public. Gzuckier (talk) 20:10, 19 February 2013 (UTC)

Note that the currently-popular RealD Cinema uses circular polarizers; it is possible to "cross" those, but it's more complicated than with the linear variety. (For instance, the two sides of a circular polarizer are not interchangeable.) --Tardis (talk) 04:42, 21 February 2013 (UTC)

A couple of "products" (I don't see any actual ordering information) that claim to do this with two different technologies:

http://www.allproducts.com/optical/hurricane/as01_print.html

http://www.photonics.com/Article.aspx?AID=29481

--Guy Macon (talk) 21:05, 19 February 2013 (UTC)

The first one claims to use my concept, but I'm confused, since they aren't circular. How could you rotate non-circular lenses relative to each other without having bits sticking out ? StuRat (talk) 21:55, 19 February 2013 (UTC)

Displacement vs. Distance

Suppose a person marks two points along the circumference of a piece of pizza. The person may measure the border of the pizza and calculate the distance from Point A to Point B along the perimeter of the pizza. That will be the distance. The displacement from Point A to Point B, if they are across from each other, would be the diameter of the pizza, while the distance, if measuring the border, is only the half-circumference of the pizza. In this example, the displacement is the shortest distance. I wonder how you apply it to the universe, which astronomers describe as being linear, parabolic or hyperbolic-shaped. The distance will probably mean how far one travels from Point A to Point B in the universe, but the displacement is presumably the shortest distance, even though this distance may be difficult to actually to calculate, because one may need to know how curvy is the curve of the universe. Is displacement really practical in the latter case? 140.254.226.230 (talk) 17:29, 19 February 2013 (UTC)

This concept of displacement requires that it be possible to embed the space in question in a higher-dimensional Euclidean space, and that there be essentially only one way to do this. In your example, the one-dimensional pizza border is embedded in our three-dimensional Euclidean space. However, there are many non-Euclidean geometries that cannot be embedded in a finite-dimensional Euclidean space, and even for those that can, the embedding is often not unique. So basically the answer is that unless an embedding space exists and we have some way of observing it, this concept of displacement is not practical. Looie496 (talk) 18:08, 19 February 2013 (UTC)

I suppose there are similar concepts in space flight. For example, the distance a space ship must travel between Earth and Pluto is not simply the minimum distance between the two, since you can't go that way. For one, the target is always moving, and, also, the spaceship will be rotating about the Sun with the velocity of Earth, more or less, once launched, not travelling straight out radially. If you add in detours around other planets on the way, the distance traveled becomes even longer.

Similarly, travel on Earth usually means along the surface, not through the crust. A great circle route is the shortest route on the surface, but detours are frequently needed, so total distance traveled from point A to B can be far more than the straight distance from A to B. StuRat (talk) 18:40, 19 February 2013 (UTC)

A great circle route is actually a good example of a geodesic. A great circle route is a geodesic within the 2-dimensional manifold of Earth's surface. Red Act (talk) 19:43, 19 February 2013 (UTC)

Although the concept of a displacement vector only really works in a Euclidean space, there's a related concept of a geodesic, which works in both Euclidean space and in a curved spacetime. Geodesics do not require any assumption that spacetime is embedded in a higher-dimensional space. Of all the spacelike curves between two events that are spacelike separated, the shortest such curve is a geodesic between the two events. In a Euclidean space, the length of the displacement vector between two points is the same as the length of the geodesic between the two points. Red Act (talk) 19:07, 19 February 2013 (UTC)

Really simple question about boiling water

I'm learning to use a wood stove that works simply by heating up and letting the warmth spread through the house, rather than through a central heating system; as such, its surface is quite hot. Upon advice from friends who have experience with these things, I've placed a small pan (one of these with the rolls removed) on top and filled it with water, so that the house will be humidified; I typically fill it by filling a cup at the sink and pouring it into the pan. The surface of the furnace is hot enough that it boils water that drips off the cup (even though it's cold water), but to my confusion, the water in the pan doesn't boil: tiny bubbles form at the bottom and the water gradually becomes steam, but despite sitting on top for hours it never boils. Why not? The Leidenfrost effect doesn't seem to apply here, since I filled the pan before starting the fire; the water has warmed gradually as the fire's gotten hotter. However, I witness the effect when little bits of water drip off the cup. Nyttend (talk) 17:48, 19 February 2013 (UTC)

Is it a cast iron stove? [[24]] spells out the basics of how this works, but cast iron heats up slowly and dissipates heat slowly - it is not a very fast conductor of heat. — Preceding unsigned comment added by 207.189.106.4 (talk) 17:57, 19 February 2013 (UTC)

It's cast iron, but I'm not sure how that's relevant. The iron under the pan (which is aluminium) is the same temperature as the iron on which little bits of water drip, so it's conducting just as much heat into the water. Nyttend (talk) 18:05, 19 February 2013 (UTC)

Aluminum foil (which this pan basically is) is a sucky heat conductor, especially given that its direct contact area with the stove is probably pretty small. I bet that you could place that pan on the stove without any water and press your finger against the bottom for a second or two without burning yourself (but if you want to try it, try a brief touch first to make sure). If you used a proper saucepan and the stove was hot enough, the water would certainly boil -- people cooked on stoves like that for ages. Looie496 (talk) 18:16, 19 February 2013 (UTC)

Aluminum isn't the best conductor, I agree. A copper pot would conduct heat better. Also, make sure that the pan is touching the stove continuously. (You sometimes get a warped pan that only touches at a few points, greatly reducing the conduction.) Ensuring that both the stove and pan are free of cruft like carbonized food is also important, as that's a good insulator, too. StuRat (talk) 18:25, 19 February 2013 (UTC)

I don't recommend this method of humidification, unless you have a freakin' big pot. The problem is that the water evaporates too rapidly, and burns the pan up when it runs dry. Also, scale accumulates on the pan as the water evaporates, leaving only it's minerals (unless you used distilled water, but that's expensive). I do actually use this method, with a huge junk stock pot at a low flame, so it takes about 2 days to evaporate. I'm unlikely to neglect it for that long. Also, note that this method of humidifying a home only makes a slight difference, as water vapor escapes through the wall cracks, chimney, etc., almost as fast as this method can add it, and, if you do manage to get the humidity up much, in winter, it may condense on nearby windows, possibly causing mold on the sills. StuRat (talk) 18:25, 19 February 2013 (UTC)

• You simply don't have enough heat capacity, meaning the temperature is high enough but the quantity of heat is not. Imagine trying to boil that water with a candle which also burns at above boiling temperature but provides only "heat quantity" for a real tiny tiny cup.TMCk (talk) 18:38, 19 February 2013 (UTC)

• I'd expect that the total heat capacity of the wood stove is more than enough to boil the water, it's just not being effectively conducted into the pan. StuRat (talk) 18:46, 19 February 2013 (UTC)

• Yes, but you don't get the whole heat capacity of the stove to the pot. (And heat is disapearing quickly once it reached the pot.)TMCk (talk) 18:57, 19 February 2013 (UTC)

Aluminium (regardless of spelling) is a very good heat conductor indeed - worse than copper, but much much better than stainless steel. See List of thermal conductivities. And that may indeed be the problem here. Heat is conducted into the pot via a relatively ineffective interface (the uneven surface of the foil on the uneven surface of the stove), and distributed very evenly through the pan. So all of the surface of the pan serves as a cooling surface, which probably keeps it slightly below 100 °C. --Stephan Schulz (talk) 20:23, 19 February 2013 (UTC)

If you have a cooking thermometer, preferably one with a probe, you could measure the temperature of the uncovered pan of water then put a cover on it and see if the temperature rises. Evaporation from the surface into the room might be keeping the temperature down. A pan or teakettle of water on a stove to humidify the air is a time-honored practice. But one small pan of water a day will not humidify a whole house very much. Edison (talk) 23:57, 20 February 2013 (UTC)

Buy a good humidity meter. Even then, they are not accurate but will serve as a rough guide ( a wet and dry bulb thermometer -even better). You may fine 35 to 40% relative humidity comfortable. A pan does not need to boil. If it does, you may end up with mildew in the colder parts of the house were it condenses. Below 40% this should not happen unless the walls/windows are very cold. The dryer the air, the more the warm water will evaporate due to partial pressure. However, by boiling, you will 'force' more water vapour into the air than partial pressure of water vapour would naturally course the water in the pan to evaporate. Which can lead to the mildew and stuff. PS. Just a little liquid water when evaporated creates an big increase in relative humidity - hence the need for a meter to see that your not over doing it. --Aspro (talk) 19:24, 23 February 2013 (UTC)

Gun safety

A lot of firearms accidents seem to involve people not realizing a gun was loaded. Why is it not possible / why hasn't it become normal for guns to be designed in such as way as to make it really obvious whether there is a round in the chamber? — Preceding unsigned comment added by 207.189.106.4 (talk) 17:55, 19 February 2013 (UTC)

It's nowhere near safe to make the round visible from the outside, since breech-loading weapons can only work if their chambers are sealed — otherwise the gases escape in wrong directions. Cartridges don't normally (in my experience) do anything to the rest of the gun when they're just sitting in the chamber, so I can't imagine a way that the presence of the cartridge could be used to change the way something else looks or feels. Nyttend (talk) 18:09, 19 February 2013 (UTC)

A few people have been in the news lately because of accidentally firing a loaded weapon that was in their breeches Gzuckier (talk) 20:19, 19 February 2013 (UTC)

Hmmm, bullets should change the ability of a magnetic field to be transmitted from one side of the chamber to the other, slightly, so you could possibly devise such a device using this principle. The added complexity of the gun might not be welcomed, though. StuRat (talk) 18:45, 19 February 2013 (UTC)

Clearly it's possible to do this. Mechanical, magnetic, electrical, optical - you can come up with a dozen ways to measure whether there is a bullet in the chamber or not. Why it hasn't become a standard feature is because there isn't a market for such weapons - people who buy weapons are clearly more concerned about cost than safety - and the legal/fiscal framework to compel such things hasn't been put in place in the target markets for gun manufacturers. A more subtle (but just as lethal) problem is that guns with magazines will typically leave one round in the chamber when you remove the magazine - and will fire it if the trigger is pulled. This fools a lot of people who think that removing the magazine unloads the weapon and many, many people have died as a direct result of this. There is a very simple, cheap fix for it that locks out the trigger when the magazine is removed - yet many weapons don't implement it. Why? It saves lives - but it's not always done. If we can't get something as simple as that fixed - then there is no chance for more difficult improvements such as you suggest. SteveBaker (talk) 20:07, 19 February 2013 (UTC)

Because in self-defense situations, it's not unusual to pop out the magazine before firing off that last round (for faster reloading) -- so if the trigger was locked when the clip is removed, it could actually cost the person his/her life. 24.23.196.85 (talk) 06:21, 20 February 2013 (UTC)

That's an idiotic argument. Tell me, how many deaths per year are caused by civilians being unable to reload in time in self-defense situations? On the other hand, this paper suggests that around 16 lives per year would be saved by these devices. SteveBaker (talk) 15:03, 20 February 2013 (UTC)

Steve, please don't use words like "idiotic" here. Always be civil. StuRat (talk) 18:53, 20 February 2013 (UTC)

Indeed. Even something as simple as allowing the hammer to rest a fraction of an inch further in when there is no bullet in the chamber to impede it, which would then actuate some sort of indicator. Gzuckier (talk) 20:14, 19 February 2013 (UTC)

Which brings up something else I've wondered about; why do some manufacturers of semiautomatic handguns (maybe other varieties, I don't know) not have a safety? Because they're designed for use somewhere where instant use is a requirement and a safety would get you shot? All I can think of.Gzuckier (talk) 20:16, 19 February 2013 (UTC)

Actually a number of handguns do include what's called a loaded chamber indicator (LCI). On my Walther PK380, it's a simple notch cut in the back in the chamber which allows you to see if a round is in the chamber. Taurus and Glock handguns designed the extractor to "pop" out just behind the ejection port. Many others do as well. However, if you search google for handguns with loaded chamber indicator, you'll see a lot of people calling them stupid. Their argument is basically that if know enough to check the LCI, then you should know enough not to be stupid with guns and if you don't know enough to be safe with guns, you won't know enough to check. You can take what you want from that argument.

To Steve Baker's question about the gun firing with the magazine out of the weapon, that's known as a magazine disconnect. Our article says they are standard on the Browning Hi-Power and some Ruger rifles and pistols. It also notes that California has required magazine disconnects since 2007. Arguments against magazine disconnects are similar to arguments against LCI's but also include the convenience of not loading a clip for a single shot. Again, make of that what you will.

Finally to Gzuckier's question. There are wide variety of safeties in use. My Walther has a external safety switch which rotates a bar that should prevent the hammer from hitting the firing pin. I actually hate that safety and don't feel very safe with it because it allows the hammer to fall and relies on the bar not bending and being in tolerance. My SIG Sauer P250 has no external safety, but it has an internal automatic safety. The firing pin is locked in place and can't move until you pull the trigger back about half way and the internal safety releases. Glock advertises that it has 3 safeties, all internal, including a trigger safety, a firing pin safety and a drop safety. So basically whether you see a safety lever or not, any gun should have at least one safety that will prevent the gun from accidentally going off.Tobyc75 (talk) 01:08, 20 February 2013 (UTC)

Of course any mechanical safety system can fail or be bypassed. The only way to truly make a gun safe is to practice safe gun handling. That includes keeping guns and ammunition secure and away from children. It includes teaching children that guns are not toys and how to safely hand one. Finally it includes keeping them away from those who would harm themselves or others and addressing the problems or illnesses that make them a hazard.Tobyc75 (talk) 01:17, 20 February 2013 (UTC)

Thanks - interesting - Toby - to your point, I'm just astonished that police and military, who are presumably among the best trained in gun handling, still manage to end up confused about whether there is a round in the chamber. — Preceding unsigned comment added by Tilapidated (talk • contribs) 05:31, 20 February 2013 (UTC)

Loaded chamber indicators are actually VERY common on all but the cheapest firearms (for example, my Beretta has an extractor that sticks out and shows a small red panel when there's a round chambered); however, they are NOT foolproof, and even if it shows the chamber to be unloaded, you should still pull back the slide and take a look with your own eyes, just to make doubly sure. 24.23.196.85 (talk) 06:26, 20 February 2013 (UTC)

You'd think they could design one which sometimes incorrectly says it's loaded, but never incorrectly says it's unloaded. Shining a laser thru a pair of tiny holes in the barrel, such that it would have to pass thru the bullet to indicate an empty chamber, would be one such design. StuRat (talk) 06:35, 20 February 2013 (UTC)

Lasers require a power source, though. Lasers run out of juice, what happens? Does it just not register a bullet? (Bad) Does it refuse to disengage the safety? (Really bad if you're in a life-threatening situation) Unfortunately, it's just not practical. — The Hand That Feeds You:^Bite 12:26, 20 February 2013 (UTC)

I wouldn't make it disable the gun. If the battery was dead it just wouldn't indicate that the chamber is empty (which a light would indicate if the battery had juice when the chamber was empty). So, it would be back to the original gun, where you can't tell if it has one in the chamber or not. StuRat (talk) 18:57, 20 February 2013 (UTC)

Again this says that 20% of the roughly 450 deaths due to handgun accidents in the USA every year would be prevented by this device - 85 people a year would not be dead if such devices were universal. How many people would die each year due to forgetting to change the battery and then entering into a life-threatening situation when actually discharging their gun would save their lives. Numbers please? SteveBaker (talk) 15:28, 20 February 2013 (UTC)

Read more: http://www.time.com/time/magazine/article/0,9171,152446,00.html#ixzz2LS9ntPcI

Re: cops & military, they're still human. Even with all the training in the world, someone can be absent-minded or careless. Especially if something becomes routine (cleaning a gun), it's way too easy to fall into a habit of not checking because you "know" you unloaded it, just like last time. Except you didn't this time... — The Hand That Feeds You:^Bite 12:33, 20 February 2013 (UTC)

There was a case in the military recently[25] where a trained infantryman decided to scare his buddy in an effort to cure his hiccups...shot him in the head by mistake. Not just because he pulled the trigger by mistake, not just that he had a live round chambered when he thought it was a blank - but also because he thought that a blank fired at short range would be safe...three mistakes in a fully trained man who was around guns all the time. Whatever happened to "Never point a gun at something you don't want killed"? No amount of training stops this kind of ridiculous stuff from happening. SteveBaker (talk) 15:03, 20 February 2013 (UTC)

A good story sure saves a person a lot of years in prison, even when nobody believes it. Wnt (talk) 17:30, 20 February 2013 (UTC)

From Gun safety:

"Treat firearms as if they are loaded

This rule is a matter of keeping a certain mindset. The purpose is to create safe handling habits, and to discourage reasoning along the lines of, "I know my gun is unloaded so certain unsafe practices are OK." The proposition "the gun is always loaded" is used as a shorthand, even though it may be assumed—or even positively known—that this is not true of a particular firearm.

Many firearm accidents result from the handler mistakenly believing a firearm is emptied, safetied, or otherwise disabled when in fact it is ready to be discharged. ... If a handler always treats firearms as capable of being discharged at any time, the handler is more likely to take precautions to prevent an unintentional discharge and to avoid damage or injury if one does occur." --Guy Macon (talk) 08:55, 20 February 2013 (UTC)

That rule would also have saved the life of Jon-Erik Hexum, who made a different error — he believed, correctly, that the cartridge was a blank, but was (apparently) not aware that discharging a blank cartridge at close range is potentially lethal. --Trovatore (talk) 08:59, 20 February 2013 (UTC)

On a related note, a local man died last year because he was showing off the safety features on his new gun. Pointed the gun at his head & pulled the trigger... but he hadn't fully engaged the safety, so it slipped.

Safeties are good, but they are not guaranteed to protect you, especially from user error. Just like a seat belt can help save your life in a car accident, but not if you failed to lock it fully in place. — The Hand That Feeds You:^Bite 12:35, 20 February 2013 (UTC)

If that gun incident didn't make the Darwin awards, it should have. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:41, 20 February 2013 (UTC)

Hey, we agree on something! :) Wnt (talk) 17:26, 20 February 2013 (UTC)

I feel confident in saying that "Try not to shoot yourself in the head" does not constitute medical advice. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:41, 21 February 2013 (UTC)

Re: the laser — that's still a hole in the chamber through which gases would inappropriately be escaping, so it would be a bad idea regardless of the laser's merits. Nyttend (talk) 12:36, 20 February 2013 (UTC)

http://injuryprevention.bmj.com/content/9/4/307.abstract bears reading. SteveBaker (talk) 15:03, 20 February 2013 (UTC)

• My Ruger mark III has a Loaded chamber indicator and cannot fire without a magazine.165.123.233.100 (talk) 17:48, 20 February 2013 (UTC)

• "Treat firearms as if they are loaded:" I still concur whole hardheartedly with Guy Macon . A ten year old properly drilled in gun safety until it become automatic will follow through on auto-pilot even when he grows older and gets his conscious mind distracted by the odd pretty looking girl passing by. A few colour photographs of the result that can come from accidental discharge adds encouragement to follows the rules until it becomes automatic. Little fancy indicators as an aid memoir are no substitute for repetition of action. I'd feel safer with a kid taught this way than with an adult that has just bought his first real gun. The big problem is, that these ruddy kids are usually better shots than I am; dam-it.--Aspro (talk) 18:21, 20 February 2013 (UTC)

• I agree completely. Even when I take a firearm out of a case, and I know I was the last one to touch it, I always check to see if it is loaded. It only takes one mistake to ruin a life.130.91.93.207 (talk) 18:50, 20 February 2013 (UTC)

• Exactly. You know that it was unloaded but you still check -every-time. It is not being over-cautious it's just automatic good gun sense. And it takes no effort when it has become automatic - in fact, it it goes against the grain to to try and behave differently. There is no excuse for accidentally discharges.--Aspro (talk) 19:02, 20 February 2013 (UTC).

I used to look at the reinsurance claims for the National Rifle Association's death and dismemberment policies, from a safe distance (London). Goodness, what a lot of foolish people. My favourite was an idiot who caught the trigger on a coat hook on his bedroom wall and shot his own leg - it was dismemberment insurance, so it must have been amputated later. The rather sadder ones were people who killed or maimed their own children, or allowed them to play with their loaded guns with predictable results. Get a safer hobby. Using the figures in the BMJ article linked by SteveBaker above, it seems that there were 1,005 firearms-related accidental deaths in the US in 2000. Alansplodge (talk) 21:59, 22 February 2013 (UTC)

Vacuum metastability event implosion?

All the sources I've seen state that freeing ourselves from the current horrid false vacuum where we slog along hindered by the heavy shackles of the Higgs mechanism will cause a zero mass vacuum state. Is there any chance it will do the reverse and unmask the "true weight" of all the virtual particles causing a sudden Big Rip? Hcobb (talk) 18:52, 19 February 2013 (UTC)

If you have a good internet source for what your talking about could you do me the favor of linking to it? I'd like to read it. μηδείς (talk) 19:15, 19 February 2013 (UTC)

It depends a bit on what you mean. If you define the "true vacuum" as a state where the vacuum expectation of all fields is zero, then that is pretty much equivalent to eliminating the Higgs mechanism and assuming all particles are massless. However, it isn't entirely obvious whether such a state would have lower total energy than our current state, or whether there are stable states intermediate between the current state and true vacuum. One can imagine that there might exist other stable vacuum configurations where the universe effectively has different physical coupling constants and the masses of fundamental particles are very different than their present values. However, we don't really have a concrete theory for why any of the coupling constants have the specific values that they do. Without an understanding for why the universe has the physics that it does, it is deeply speculative to imagine fundamental changes to that physics. So while it is in some sense "possible" under some theories that the universe could move to a configuration with very different masses (even heavier masses), such theories are essentially untestable within the limits of our present understanding, and hence we can't really draw many meaningful conclusions about such a possibility. Dragons flight (talk) 00:27, 20 February 2013 (UTC)

Vacuum metastability and the Higgs mechanism are two different things. The Higgs mechanism works because the "true" vacuum state of the Standard Model has a higher energy than nearby non-vacuum states, so it's inherently unstable (not merely metastable), and as the universe cools it inevitably ends up in a minimum-energy non-vacuum state, and we are small perturbations of that state, which we normally think of as the vacuum. It would make sense to call this a "false vacuum", but I can't remember ever hearing the term used in this context. There is no way the universe could ever "end up in" the true vacuum of the Standard Model since that is still as unstable as it ever was. Vacuum decay, on the other hand, happens when there's another vacuum that is stable and has a lower energy than our pseudo-vacuum, but is separated from it by a huge potential barrier, so our vacuum is almost stable but eventually will tunnel to that lower-energy vacuum. Our vacuum is called a false vacuum in that context. There may be no such lower-energy vacuum; if there isn't then our pseudo-vacuum is completely stable. Tunneling to a lower-energy vacuum leaves the energy difference in the form of real particles, so it does effectively "unmask the true energy density" of the false vacuum. I'm not sure that could be considered the energy of virtual particles. Different vacua effectively have different particles (virtual or real) and different laws of physics. Familiar particles like electrons make no sense in the true Standard Model vacuum, though technically all the pieces are there. -- BenRG (talk) 08:02, 20 February 2013 (UTC)

applications

what are the applications of the ultra thin capacitors? — Preceding unsigned comment added by 115.240.6.7 (talk) 19:20, 19 February 2013 (UTC)

Film_capacitor#Applications. SteveBaker (talk) 19:57, 19 February 2013 (UTC)

Speakers & moisture/humidity

Can you tell whether audio speakers have been damaged from humidity? Are there any specific kind of noises or loss of sound quality it might have? Thanks. Clover345 (talk) 21:06, 19 February 2013 (UTC)

Paper cone woofer? Polymer dome tweeter? Horn?

The basic tests you want to do are a complete visual inspection, then run some very low frequency tones (not too loud!) and listen for anything rubbing or rattling. Something like this: http://www.youtube.com/watch?v=BdQbQa-rIbw or this: http://www.youtube.com/watch?v=lfXXQfG1T3g --Guy Macon (talk) 23:06, 19 February 2013 (UTC)

How long was it humid for? This might allow mould to grow on the cone (is there antifungal agents doped onto the it?). CS Miller (talk) 23:22, 19 February 2013 (UTC)

Unless you plan to buy them, sell them, or make an insurance claim, wouldn't it just be easier to continue using them, and, if unsatisfactory, replace them ? That is, if they are damaged, but you can't tell by normal listening, does it matter ? StuRat (talk) 23:26, 19 February 2013 (UTC)

I have a feeling the sound might have got a bit cloudy Clover345 (talk) 23:46, 19 February 2013 (UTC)

Leave them in a warm, dry, well ventilated area for a day or two. Might be that the cones are damp and therefore heavier then what they should be. It's possible that could affect the sound. Vespine (talk) 02:39, 20 February 2013 (UTC)

I imagine it might differ by type of suspension; acoustic suspension (i.e. sealed box) shouldn't be affected too much, but the kind where the cone is suspended by a zigzag support of resin impregnated fabric or some such might well be affected by moisture/humidity. (In addition to how the stiffness of a cardboard type cone would affect breakup, traveling waves, etc.) Gzuckier (talk) 20:53, 20 February 2013 (UTC)

February 20

Recurring smell

we can't give diagnoses or medical advice
The following discussion has been closed. Please do not modify it.
Hello all, there's something I'm wondering about. Just today, there was an incident at the refinery: a flange joint in one of the petrochemical units let go and caused quite a large spill of acetic anhydride. Thank God we contained it quickly and nobody got hurt, but the vapors entered the control room through the HVAC system and stank up the place pretty bad. I, in particular, inhaled a rather large amount of the vapor -- I didn't evacuate because I was too busy shutting down the unit, and I had tossed my gas mask to a young white lady who had lost hers, and who also had to stay at her post. To make a long story short, I had one of the highest exposures to the chemical, but I was fine (except for developing a runny nose and a slight cough). My question, though, is about a unique experience I had some hours after the incident: I had smelled the distinctive stench of the anhydride at the time of the incident, but it went away after the vapor dissipated -- however, and that's the unusual part, when I ate a tomato for dinner a few hours later, I instantly smelled acetic anhydride once again! Why is that? Did I have some of that stuff stuck to the back of my throat all that time between breathing it in and eating a tomato? Or was there something else at work? Thanks! 24.23.196.85 (talk) 07:10, 20 February 2013 (UTC) Oops, forgot to sign my comment. Fixed now. 24.23.196.85 (talk) 07:11, 20 February 2013 (UTC) Possibly related to Olfactory fatigue but consider seeing a doctor. Rmhermen (talk) 07:35, 20 February 2013 (UTC) Could also be some of the vapour was still in the bottom of your lungs, and you took a slightly deeper breath than usual when eating the tomato. 124.191.176.222 (talk) 07:44, 20 February 2013 (UTC) I didn't think that was produced from oil, does petrochemical works here just mean general chemical works including oil products or does it really use oil originally? That was dangerous not having proper safety equipment easily available for all staff who might be present whatever about them not individually following regulations. Dmcq (talk) 09:27, 20 February 2013 (UTC) One should not exclude the possibility that this story is made up. This IP asks a lot of weird questions. Looie496 (talk) 16:44, 20 February 2013 (UTC) I can't speculate with any certainty, but what we do know is that acetic anhydride is not stable in the presence of water, so it didn't "adsorb" and hang on unnoticed. I wonder if there is just maybe a chance that some fairly dry mucosa in the throat could react with it in the gas phase (to become <something> acetate) and then release the acetate by acid hydrolysis. I should echo other sentiments that I'm answering this solely as a gee-whiz question - if you have any reason to feel that this symptom is somehow unpleasant or harmful, or if you are concerned about your health, this isn't an answer worth consulting and you know where to get one. Wnt (talk) 17:24, 20 February 2013 (UTC) we can't give diagnoses or medical advice μηδείς (talk) 23:34, 20 February 2013 (UTC)

Not medical advice, just wondering. For the record, I did see a doctor that same day and he told me I should recover completely in a few days. And yes, the plant does make acetic anhydride (among many other things) from the ethylene produced by the FCC unit. 24.23.196.85 (talk) 06:40, 21 February 2013 (UTC)

Good to hear that. And thanks very much, I should really have checked with Google as it knows a lot more than me and is more up to date ;-) Dmcq (talk) 17:13, 21 February 2013 (UTC)

Rubbing two stones

When we rub two stones a spark is produced. How is this spark produced? I think this is due to electric discharge. 106.218.237.192 (talk) 08:30, 20 February 2013 (UTC)

It depends on the stones and on the type of spark. There are at least three possible processes. Triboelectricity, which is produced by rubbing any two materials together, and piezoelectricity, produced by distortion of certain crystalline materials (and used in some barbecue igniters) both produce purely electric sparks. The sparks seen with flint and steel (or flint and iron pyrite) are actually tiny particles of iron being shredded off and burning rapidly in air. TenOfAllTrades(talk) 14:34, 20 February 2013 (UTC)

Note, though, that most "flints" these days are actually man-made ferrocerium, where the steel scrapes off small shavings of ferrocerium, which then ignite. This is backwards from traditional flints, which, as you mention, make sparks by scraping off and igniting pieces of the steel. -- 205.175.124.30 (talk) 19:52, 20 February 2013 (UTC)

When stones hit each other they do so at point, which concentrates a lot of energy into that point. Because stones are made from hard minerals that do not deform much, that energy is not spread around so much, but instead heats and breaks off that point to make a hot flying fragment of mineral, a spark. Graeme Bartlett (talk) 20:32, 20 February 2013 (UTC)

Do the two stones become charged when they produce spark? Is this spark produced due to electrons or due to huge energy? 106.218.108.227 (talk) 02:14, 21 February 2013 (UTC)

Space-time

We know our sun has created a huge depression in space-time and the earth revolves around the sun in that curvature. Anything revolving around a curved surface roll down below the base of the surface. Why don't earth roll down below the center of that depression made by sun? 106.209.197.10 (talk) 10:05, 20 February 2013 (UTC)

Because the depression is not two-dimensional, as is commonly shown in poorly-diagrammed science shows. The depression is three-dimensional, and the Earth accelerates toward the sun's center of mass, not toward an imaginary point beneath it. Evanh2008 ^{(talk|contribs)} 11:02, 20 February 2013 (UTC)

Because the earth has velocity perpendicular to the direction of the sun. Even in the oversimplified 2D model with depression in the third dimension a ball with initial velocity would not fall in straight but spiral in. And this only because it looses kinetic energy due to friction. Without friction, it would circle around the depression endlessly. 95.112.187.252 (talk) 12:03, 20 February 2013 (UTC)

It should be noted that there really is no depression at all, that's just an aid to visualizing the scenario. In relativity, objects move along geodesics in curved space -- in other words, gravity causes a curvature of space, and objects move through that curved space as if no force was acting on them. But when you have a ball rolling near a depression, you need an external downward force to get anything that resembles gravity. Looie496 (talk) 16:40, 20 February 2013 (UTC)

Newtonian gravitational potential

General relativistic spacetime curvature

If you see a picture like the first one on the right, it's a graph of the Newtonian gravitational potential, and you can think of objects moving in that potential as rolling along it under the action of a constant downward vertical force. If you turned the graph upside down the direction of the apparent central force would switch from attractive to repulsive. This has nothing to do with general relativity, despite what you'll read in a lot of books.

If you see a picture like the second one, that's a genuine embedding of general relativistic spacetime curvature. It's a surface in 3D space, not a graph. Because only the curvature matters, turning it upside down (or sideways) makes no difference; the effective force is always attractive. To see why, you can cut out a circular piece of paper, draw a straight line (chord) on it, cut out a narrow pie slice that doesn't intersect the line, tape the two edges of the slice together so you have a cone, tape it to a flat sheet of paper, and temporarily flatten the cone near the ends of your chord so that you can continue it to a straight line on the flat sheet of paper. You will find that the line as a whole curves toward the central point, even though it's locally straight everywhere. Of course it would be the same if you had taped the cone underneath the paper instead.

All that said, the earth doesn't fall directly into the sun because it's in orbit, and it doesn't spiral into the sun (on any realistic time scale) because there's very little friction. Incidentally, I seem to recall that if gravitation were a vector force like electromagnetism, the earth would have spiraled into the sun by now. Gravitational friction is much lower because there is no gravitational dipole radiation, only quadrupole radiation and above. -- BenRG (talk) 18:33, 20 February 2013 (UTC)

Even in that Newtonian scenario the picture is only a visualization aid. If you think of the height as the potential energy, then a vertical slope would correspond to an infinitely large force. But an object falling into a hole does not experience an infinite force when the walls of the hole are vertical. It's still just a metaphor, not to be taken too literally. Looie496 (talk) 19:38, 20 February 2013 (UTC)

It's more than just a visualization aid. In a constant vertical gravitational field the height is proportional to potential energy, so a small object resting on a properly scaled potential energy graph will actually have the correct potential energy. When it's moving, though, it has too much kinetic energy because of vertical motion and rotation. You could minimize friction and solve the rotation problem by using a sliding puck on a curved air hockey table. I don't see how to solve the vertical motion problem, though. -- BenRG (talk) 22:37, 21 February 2013 (UTC)

The mass of the solar system is slightly less than the masses of sun and planets individually

Well, we all know the reason why the mass of atomic nucleus is slightly less than the masses of neutrons and protons individually. The mass of the solar system is slightly less than the masses of sun and planets individually. What is the reason behind the second statement ? Technologous (talk) 11:53, 20 February 2013 (UTC)

Where did you see the second statement? If the sum of a list of masses is different from that shown for the complete system, it could just be due to rounding. Rojomoke (talk) 13:30, 20 February 2013 (UTC)

In this section of article "mass-energy equivalence" Technologous (talk) 13:43, 20 February 2013 (UTC)

It's nonsense. The Solar System consists of far more than the sun and planets.--Shantavira|^{feed me} 14:07, 20 February 2013 (UTC)

Whoa, let's not get carried away with the 'n-word'. If we take "the sun and planets" as shorthand for "all the mass in the solar system" (or, alternatively, the "the solar system" to mean just the Sun and its planets, and ignore the gas, dust, comets, asteroids, and all the other minor planetary detritus) then the statement actually does make some sense—if one is very careful in the way one chooses to define "mass". It is a restatement of the principle that any gravitationally bound system will have an apparent mass that is less than the sum of the masses of its constituent parts, if those parts were separated. The energy of any gravitationally-bound system is lower than the energy of free particles (or planets) by the amount of their gravitational binding energy; by mass-energy equivalence, the apparent mass of the gravitationally-bound system is lower as well.

That said, I haven't run the numbers through but I would be very surprised if the difference in apparent mass actually came out to be more than rounding-error-sized for any body in our solar system. More interesting results might be obtained for bodies in close orbit of neutron stars or black holes. TenOfAllTrades(talk) 14:28, 20 February 2013 (UTC)

It is in the noise, but perhaps not as far in the noise as one might guess. The gravitational binding energy of the Sun is slightly more than the mass-energy of the entire Earth. Dragons flight (talk) 18:45, 20 February 2013 (UTC)

Question about a strange polymer

I had a strange dream about a polymer yes I know this is kind of perverted. Now I wonder if there is any chance of knowing the properties of this polymer.

The base molecule was pentane modified to have 2 adjacent ketone on one end and a double bound on the other, H(CO)-(CO)-(CH2)-(CH)=(CH2) (I know the first group really is an aldehyde as long as not polymerized, and polymerization would probably destroy the O-double-bound rather than remove the H). On the completed polymer there were also side-chains one on each base molecule. The dream was not clear on how they were attached, but it was -(CH2)10-(C6H4)-Cl, whit the chlorine in para position.

Thanks for any clue about that. 95.112.187.252 (talk) 12:23, 20 February 2013 (UTC)

There seem to be two steps to the question here. The first, of general interest, is "what properties does an unknown polymer have?" for us to measure. I'd like to hear that. The second involves guessing out the answers to those, and is more problematic.

Nonetheless, I assume anything with those long saturated carbon chains would be very oily, and with so much of the polymer made up of dead-end chains, I assume it wouldn't be very strong. I kind of wonder if the Cl's could make it possible for it to work like phospholipids or a soap, forming micelles and vesicles and such, but I suspect there isn't really enough polarity there to make it work very well. Wnt (talk) 17:43, 20 February 2013 (UTC)

Well, I didn't have the hope that this polymer was known by some name or had a wiki page of it's own. In the dream it was indeed oily, milky in appearance with a yellowish hue, building sharp droplets as if from a high surface tension. The two adjacent ketone groups featured really prominent, and I wondered (even inside the dream) if such thing could be stable at all. Another thing was that it was a conductor for electricity. Is there any chance of that, or can that be excluded by the structure? Another curious thing was that, as a kind of secondary structure, four of those chains would be entwisted into one, somehow in the way two DNA strains are twisted into one, but with the side-chains still pointing outward. Is anything like that known to happen in real live? 95.112.187.252 (talk) 20:46, 20 February 2013 (UTC)

Well, vicinal diketones like diacetyl and pentanedione do exist. I wish I were more qualified to say what properties they have... Wnt (talk) 00:32, 21 February 2013 (UTC)

For a polymer to conduct electricity, it must have conjugated pi-bonds (as in the case of polyacetylene, for example). 24.23.196.85 (talk) 06:43, 21 February 2013 (UTC)

Agreed - sorry, forgot about that part. I came up with a search result that acetone has conductivity 0.02 uS/cm (18 C) to 0.06 uS/cm (25 C). I'm having an amazing amount of difficulty deciding whether that is really equal to 2 uS/m as the math suggests, but in any case it is somewhere well under that of water. But I didn't find a figure for diacetyl to compare. Wnt (talk) 17:34, 21 February 2013 (UTC)

Momentum gained by body = Force x Time during which force acts

How can we proof that Momentum gained by body = Force x Time during which force acts ? Not homework. — Preceding unsigned comment added by 106.209.218.22 (talk) 13:21, 20 February 2013 (UTC)

There is useful information in momentum. -- SGBailey (talk) 16:20, 20 February 2013 (UTC)

If we define force as the rate of change of momentum with respect to time then change in momentum is the integral of force with respect to time. If a constant force is applied for a given time interval then this simplifies to give us change in momentum = force x time interval. Note that in the general case both force and momentum are vectors. Gandalf61 (talk) 07:23, 21 February 2013 (UTC)

Tonsillar cancer

Do we have an article dedicated to cancer of the tonsils, and if so, what is it? Tonsil and Oral cancer mention it somewhat, but only in passing, while Palatine tonsil doesn't mention cancer at all. Tonsil cancer and Tonsillar cancer could stand to be created as redirects, but I'm not sure what their targets should be. Nyttend (talk) 19:30, 20 February 2013 (UTC)

Tonsils are lymphatic tissue, so I would guess that tonsil cancer would fit under Lymphomas. Not sure, but that'd be my best guess. --Jayron32 20:14, 20 February 2013 (UTC)

No, lymphomas are blood cancers. It's the lymphocytes themselves that proliferate, not the solid tissues they're associated with. --Trovatore (talk) 20:19, 20 February 2013 (UTC)

See Oropharyngeal cancer. Duoduoduo (talk) 20:27, 20 February 2013 (UTC)

Liquid with highest boiling point

Resolved

Of all reasonably non-flammable substances that are liquid at room temperature, which has the highest boiling point? Horselover Frost (talk · edits) 23:20, 20 February 2013 (UTC)

Well mercury has a reasonably high boiling point of 356.7 °C (note that mercury vapor is toxic). And gallium has a melting point just above room temp, at 29.78 °C, but a boiling temp way up at 2403.0 °C. Alloys of gallium, such as galinstan, are liquid at room temperature, but also have a bit lower boiling temperature, although still > 1300 °C. StuRat (talk) 23:31, 20 February 2013 (UTC)

A quick look shows that not only is gallium perfect for what I had in mind, it's already used in similar applications. Thanks! Horselover Frost (talk · edits) 21:51, 21 February 2013 (UTC)

You're quite welcome. I'll mark this Q resolved. If you disagree, please remove the resolved tag. StuRat (talk) 04:59, 22 February 2013 (UTC)

What about some of the high melting point glass types? Glass is chemically liquid at room temperature isn't it? Or do you mean runny liquid? --BozMo talk 23:39, 20 February 2013 (UTC)

Glass is a brittle solid at room temperature, per the article, not a liquid. Glass lenses hundreds of years old and Roman glass a couple of thousand years old have retained their shape. Edison (talk) 23:47, 20 February 2013 (UTC)

I've heard glass referred to as a "supercooled liquid", as per window glass which can shrink from the top over the course of many decades. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:51, 20 February 2013 (UTC)

That's just an urban legend[26][27][28]. Some builders took the time to install the thinner side of the glass up, some didn't.Dncsky (talk) 23:55, 20 February 2013 (UTC)

Glass is properly an amorphous solid which is a phase of matter that lies somewhere between a solid and a liquid. It is liquid-like in the arrangement of the molecules: they are not arranged in an organized crystal lattice like other solids, instead they are arranged in a liquid-like organization. However (and this is a big however), the molecules themselves don't have any translational motion: that is, individual molecules remain "locked in" to their location in the glass, which is the basic definition of a solid. The main component of glass, silicon dioxide has crystalline solid forms (quartz), glass being the non-crystalline solid form of silicon dioxide. However, glass is still unambiguously a solid. Just one with a liquid-like organization. --Jayron32 02:44, 21 February 2013 (UTC)

What it doesn't have, though, is any well-defined melting point. --Trovatore (talk) 03:38, 21 February 2013 (UTC)

That's tautologically the definition of a "glass". See glass transition. --Jayron32 04:26, 21 February 2013 (UTC)

Perhaps, but it seems like thermoplastics are similar, in this respect. For that matter, so are oils and gels. StuRat (talk) 05:26, 21 February 2013 (UTC)

February 21

Mercury thermometers

Mercury thermometers become more inaccurate over time. Do they record (overly high) tempatures, or overly low tempatures when they are too old?149.152.23.48 (talk) 00:36, 21 February 2013 (UTC)

I added a title. StuRat (talk) 00:43, 21 February 2013 (UTC)

Note that, if they did drift, all they would need is to be recalibrated (have new numbers painted on). StuRat (talk) 00:45, 21 February 2013 (UTC)

Who says they loose accuracy over time? Accuracy is determined by three things: Random error in taking readings - in the conventional mecury thermometer this is merely a factor of how carefully one looks at the scale and compares it to the mercury height; Systematic error, which is determined by the accuracy of calibration (the position of the glass tube with respect to the scale, accuracy of capilliary diameter), and drift.

In metrology generally, drift is made up of thermal drift, inapplicable to thermometers as it is taken up in calibration, drift over time, and noise. There are no significant time and noise drift mechanisms for normal sealed mercury-in-glass thermometers.

Possibly the OP is referring to sensor thermometers that were once used in photographic processing labs, chemistry labs, and industrial control systems. In these, the mercury is electrically earthed via a wire sealed into the glass at the bulb end, and there is a probe wire fed in via a hole in the glass at the top end. The probe wire is adjusted in position so that at the desired temperature, it just touches the mercury column. When it does, it closes an electrical circuit, which controls the tank heater or whatever is required. These thermometers, when new, are extremely accurate compared to alternatives at the time. However, as the probe wire must move freely in the hole, there is not a perfect seal, and over tens of years some mercury vapour can escape to atmosphere, leaving less in the tube. So, over time, the thermometer reads lower and lower compared to the calibrated temperature. These wire probe type mercuray thermometers have been obsolete for 40 years or more, as solid state electronic thermometers (quartz or platinum sensing) were developed with more than adequate accuracy for the purposes that a mercury thermometer would otherwise be used. But you still sometimes see them. I saw one still in use in a photographic lab only a few years ago.

Ratbone 60.230.238.153 (talk) 03:14, 21 February 2013 (UTC)

In general, mercury thermometers do not drift. However, they may become damaged. Sometimes an old thermometer will have discoloration of the mercury or even bits of oxidized mercury along the capillary. This is caused by improper filling, where moisture or air was sealed inside the instrument. On high temperature thermometers, sometimes a portion of the column evaporates and then condenses in the upper portion of the thermometer. If a thermometer is treated roughly or thermally shocked, it can develop a nearly invisible stress crack, allowing mercury to escape. because of these effects, mercury thermometers need to send out for calibration, but the calibration is not because of any natural drift but because a close visual inspection under a magnifier followed by checking the accuracy is the most reliable way of identifying the above problems. --Guy Macon (talk) 08:27, 21 February 2013 (UTC)

We have several Mercury-in-glass thermometers provided by Environment Canada. Every one of these comes with a correction chart made up by EC. The oldest card and thermometer we have is dated 1978 and is still in use. There are two possibilities that could lead to inaccurate readings. First is if the column of mercury was to separate into two columns. Second, mercury freezes at −38.8 °C (−37.8 °F) and leaving them out at temperatures colder than that may cause problems. I wonder if the OP is thinking of mercury barometers rather than thermometers? It's been a long time since we used one but I seem to recall that the inspectors would check them out every time they were on a site visit. Also the mercury could be drained out for shipping which indicates that, unlike the thermometers, they were not sealed units. CambridgeBayWeather (talk) 01:02, 22 February 2013 (UTC)

Signs of life on Titan and Europa?

Do any of life currently exist on Titan. I thought Titan is way too cold to even support life. Its average surface temperature is -185 C/-300 F. I know Titan currently have water and rains. Some scientist thinks life could exist on Europa's ocean possibly sharks or maritime life. i wonder how is that plausible since Europa's surface is too cold -160 C/-260 F. Does this matter if planet fits under habitable zone to be habitable ? Or most important factor for habitable planets is water and atmosphere?--69.226.39.147 (talk) 01:22, 21 February 2013 (UTC)

If NASA had discovered unambiguous signs of life, I'm sure we would know about it. It is possible for life to not exist on the surface, and to only exist deep underground (or underwater). On Earth, we both have bacteria which live deep underground and live off minerals there and whole ecosystems around hydrothermal vents on the ocean floor, which get their energy from places other than sunlight, such as radioactive decay. Tidal forces could provide energy on the moons of the Jovian planets. If the energy sources are quite limited, you might find the plants and animals there have a much slower metabolic rate, and therefore grow and move more slowly. StuRat (talk) 01:38, 21 February 2013 (UTC)

We have an article on life on Titan. The corresponding article for Europa is a subsection only, mostly because there's virtually no hard evidence to go on (we have attempted no landings there). Due to the good chance of Europa having a subsurface liquid water ocean, my understanding is that it's considered to be a stronger case for extraterrestrial life than Titan; we just don't have as much evidence to examine. I note particularly that I find Stu's initial comment a little vague, mostly because of the various ways it can be interpreted. The Cassini-Hyugens mission found data from Titan that could be the result of biological processes, but could also be from other natural processes. Is that a sign of life? Maybe, depending on your definition. Even this tenuous bit should cast doubt on a blanket claim of "if there were, I'm sure we would know". — Lomn 01:50, 21 February 2013 (UTC)

Ok, let me add the word "unambiguous". StuRat (talk) 01:54, 21 February 2013 (UTC)

Even then, there are vagaries regarding just what "signs" of life are, and whether they're actually related to life, or whether "we" is "we the human race" vs "we the ref desk". Mostly I'd suggest sticking to a more straightforward referenceable statement like "Scientists do not currently know of extraterrestrial life on Titan or Europa, though it has not been ruled out" -- particularly for a leading sentence -- but that may just be the pedant in me. — Lomn 02:03, 21 February 2013 (UTC)

Oh come on, we don't need to be so pedantic, especially if it has a chance of confusing the OP. An unambiguous sign of life would be if a probe sampled the ocean on Europa and saw non-terrestrial microbes with its microscope. A even more unambiguous sign would be if a giant squid attacked the probe with its tentacles, and the probe took a picture of it. In any case, for any reasonable definition of "unambiguous", nobody has detected unambiguous signs of past or present life anywhere except Earth. --140.180.243.51 (talk) 03:37, 21 February 2013 (UTC)

For an interesting fictional treatment of life on Europa, see 2010: Odyssey Two. --Jayron32 02:01, 21 February 2013 (UTC)

"I know Titan currently have water and rains."

Titan has lakes and rain, but they're composed of simple hydrocarbons like liquid methane and ethane, not water.

"i wonder how is that plausible since Europa's surface is too cold -160 C/-260 F"

Both Titan (moon) and Europa have global subsurface oceans. Titan is 50% ice, which corresponds to many orders of magnitude more water than exists on Earth. Europa has a more rocky composition, but it still has a layer of liquid water 100 km thick, which corresponds to 2 times the mass of water on Earth. As for why these subsurface oceans can exist, it's mostly due to tidal heating. The moons orbit close enough to their planets that their near side feels significantly more gravitational force than their far side, causing them to be stretched. This stretching releases heat through friction, which melts enough ice to maintain a liquid ocean. As you said, the surface is too cold to support liquid water, but the interior fares better because the outer ice layer serves as insulation to prevent tidal heat from escaping. --140.180.243.51 (talk) 03:37, 21 February 2013 (UTC)

Time running slowly

When the velocity of a body increases, time for that body starts running slowly. Also, when gravitational force increases, time, in this case also, starts running slowly. Here, in both cases time runs slowly. Why don't time run faster when velocity or gravitational force increases? Chi Yang --27.62.106.130 (talk) 01:58, 21 February 2013 (UTC)

See time dilation for an explanation, it isn't a simple as your original assumptions. --Jayron32 02:39, 21 February 2013 (UTC)

It is fundamental property of time. It is described accurately by spacetime which is a mathematical model that combines space and time in single entity. Gravity and velocity bends spacetime which is observed as time dilation. - manya (talk) 03:24, 21 February 2013 (UTC)

The time dilation for a moving object is relative - something not moving at that velocity sees the object's time slowing down, but the object itself (or anything moving the same speed in the same direction) does not see his time slowing down. Bubba73 ^{You talkin' to me?} 03:40, 21 February 2013 (UTC)

Calculating the electric potential between two point charges

When given the coordinates and the charges of two points, how do I calculate the voltage/electric potential present at some other coordinate? — Melab±1 ☎ 03:09, 21 February 2013 (UTC)

This is one of Maxwell's equations, specifically Gauss's law IIRC. --Jayron32 03:23, 21 February 2013 (UTC)

Gauss' law doesn't tell you the potential. See electric potential instead, specifically "electric potential due to a point charge". Potential is an additive scalar, so if you have the potential due to 1 charge, you can just add the potential due to the other. --140.180.243.51 (talk) 03:39, 21 February 2013 (UTC)

Palladium Hydride

So I am trying to figure out at what temperature Palladium Hydride releases Hydrogen? And at what temperature it adsorbs Hydrogen? How much Hydrogen can it release? Ender Wiggin (talk) 03:58, 21 February 2013 (UTC)

Pluto to have a watery surface

This is true in 7.5 billion years scientists eventually Pluto and Kuiper belt object will eventually reach habitable surface temperature [29] it shows that icy moons of outer planets can actually become a ball watery beach and it even said in 7.5 billion years as sun's giant Pluto and Charon will become a liquid beach. However most people will think when they hit habitable surface temperatures they will have technical problems is atmosphere driven off into space. (I was forced to learn when Titan and Europa hit habitable surface temperatures they will hit technical problems:Atmosphere driven off into space) Actually [30] artist's conception's image shows when Pluto warms up slightly, it can create a more substantial atmosphere, but the question will be how warm can the atmosphere survive on Pluto. Can Pluto's atmosphere survive when it gets warmer than the conditions Jupiter and Saturn's moon is now? Alot of artist conception shows when Europa gets warmer, I've watched it on Youtube video, Europa's ice can actually melt into ocean beach, but I am not quite sure on how long will the atmosphere survive there? --69.226.39.147 (talk) 05:17, 21 February 2013 (UTC)

Determining asteroid's orbits

I'm looking for a description of how Asteroid's orbits are measured/determined, and trying to get some idea of the accuracy that can be obtained. It seems pretty surprising to me that the approach distance to Earth can be worked out so far in advance, when surely there must be some close encounters with other bodies that can't be predicted, apart from the questional accuracy of the initial sightings. Thanks in advance. 124.191.176.222 (talk) 07:19, 21 February 2013 (UTC)

Orbit determination may help. Duoduoduo (talk) 20:10, 21 February 2013 (UTC)

If Einstein hadn't invented the theory of relativity, would someone else have?

if einstein hadn't invented the theory of relativity, would someone else have? or might we still not know it today (even though we would know about quantum mechanics, for example). for example simply due to lack of interest or attention. (since we were focused on other aspects of physics for example). 178.48.114.143 (talk) 07:48, 21 February 2013 (UTC)

You never know. I could be the one, if not Einstein. ;) ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 07:55, 21 February 2013 (UTC)

No, this could never be. Long before peak oil and peak copper, peak intelligence already happened around 1900. Intelligence is steadily declining since. 95.112.148.69 (talk) 12:26, 21 February 2013 (UTC)

To be pedantic Einstien did not invent the theory of relativity. He postulated it. -- Alan Liefting (talk - contribs) 08:16, 21 February 2013 (UTC)

To be pedantic, it's Einstein, not Einstien. -- Jack of Oz ^[Talk] 19:32, 21 February 2013 (UTC)

(edit conflict) As for the question, we could compare it to the classic case of two separate people putting forward the theory of evolution, namely Charles Darwin and Alfred Russell Wallace. Einstein did have an amazing insight but there is nothing to suggest that at some stage (maybe decades later) someone else would came up with the same theory. Scientific discoveries and technological developments that after Einstein postulated his theories would mean that it would be easier for other scientists to arrive at the same conclusions. -- Alan Liefting (talk - contribs) 08:24, 21 February 2013 (UTC)

• I believe that most physicists think that Special relativity would soon have been invented if Einstein hadn't -- other people were very close to it. The story may be different for General relativity -- that was a huge leap beyond anything that anybody else was doing, and even now there are only a small minority of physicists who really understand it. Looie496 (talk) 08:20, 21 February 2013 (UTC)

  All basic ingredient of special relativity had been known from works of Hendrik Lorentz and Henri Poincaré before Einstein. So, Einstein only made the last step. General relativity would have likely been discovered without Einstein as well—David Hilbert obtained Einstein equations almost in the same time and independently of Einstein. Ruslik_Zero 12:17, 21 February 2013 (UTC)

  Don't forget Hermann Minkowski who also provided much of the mathematical underpinning for both relativity theories. Minkowski basically worked out all of the geometries of spacetime prior to Einstein applying it to light (special) and gravity (general) relativity theories. Einstein did not work in a vacuum, and it is possible, even quite likely, that with all of the ingredients someone would have put it all together eventually. Unprovable, but also not out of the realm of possibility. As Isaac Newton once famously noted "If I have seen further it is by standing on the shoulders of giants." Such a sentiment applies just as well to Einstein as anyone in the sciences. --Jayron32 15:06, 21 February 2013 (UTC)

  I'm not aware that Minkowski did any work on curved spaces. Regarding Hilbert, that's true, but it raises an interesting sociological question: he was considered a pure mathematician, and it's unlikely that any physicist would have paid serious attention to his ideas (since none of them could understand the mathematics). Einstein, in contrast, was already the most famous living physicist when he presented General Relativity, due to his incredible 1906 papers. Looie496 (talk) 17:01, 21 February 2013 (UTC)

  See Minkowski space, Minkowski diagram, etc. --Jayron32 18:45, 21 February 2013 (UTC)

1905. -- BenRG (talk) 19:25, 21 February 2013 (UTC)

I tend to agree that Minkowski's discovery of spacetime was a more important breakthrough than Einstein's original paper, but Minkowski's famous talk was in 1908 and I'm pretty sure it was Einstein's paper that inspired him to work on the problem. Minkowski died in 1909 and didn't do any work on general relativity as far as I know. Einstein initially didn't like the idea of spacetime but later said that he couldn't have discovered general relativity without it. -- BenRG (talk) 19:25, 21 February 2013 (UTC)

Indeed. Minkowski was Einstein's professor in Switzerland, and the two remained life-long collaborators, frequently critiquing and adding to each other's work. Minkowski provides the intermediary link between the special and general relativity theories: he developed his spacetime geometry as a way to simplify the mathematics behind special relativity; Einstein in turn used his unique four-dimensional geometry as a launching-off point to come up with his geometric description of gravity which forms the core of General relativity. These discussions are not to discount the singular genius of Einstein. It may have taken a dozen different people another dozen years to come up with what he did in the course of a much shorter time. But to say that doesn't mean that, had he not existed, all of those principles would simply never have been discovered or elucidated at all. He did not work in a vacuum, and had he not existed, others would have filled that void. Science works by answering the as-yet-unanswered questions (and also, it should be said, by asking the as-yet-unasked questions) and had Einstein not answered them, it seems impossible that no one else would have in the intervening years. --Jayron32 20:26, 21 February 2013 (UTC)

So far, the responses have focused on "how close" others were to Einstein's general theory. It sounds like the person who was closest, Hilbert, was doing pure math. That leaves the question of whether - even if someone had equations close to Einstein's - anyone would have given the specific thing great attention. (For a moment, let us say that Hilbert moved on to other things or whatever, like leaving equations in a notebook). Is it "natural" to develop the general theory of relativity, from the things that everyone was already looking at, such as the speed of light? Was there any particular reason to look deeply into that direction? What I mean to say, is that it is easy for me to imagine that, as quantum mechanics developed as something that physicsists could experiment with, and as in a practical sense everyone uses QM every day in electronics, etc, it is easy for me to imagine that we have QM today but nobody has invented general relativity. That would only be possible if it were possible for physicists not to really focus on the space that General Relativity is in . Could that have happened? How obviously was it in need of physicists' attention? 178.48.114.143 (talk) 18:39, 21 February 2013 (UTC)

From a modern perspective general relativity is the only relativistic field theory satisfying some pretty simple constraints (spin 2, no derivatives higher than the second... that may be all), so I'm sure it would have been discovered at some point. I'm actually kind of surprised it took Einstein 11 years. He had to discover almost everything from scratch, but still, it's not that hard. Part of the reason is that he lost several years to the hole argument.

It's sort of off topic, but one area where Einstein's influence seems to persist is in the typical presentation of the ideas he originated. Look at the lede of our article on general relativity: "General relativity [...] is [a] geometric theory of gravitation [...] the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present", etc. Now look at the lede of the article on gauge theory: "[A] gauge theory is a type of field theory in which the Lagrangian is invariant under a continuous group of local transformations. [...] The transformations between possible gauges [...] form a Lie group which is referred to as the symmetry group or the gauge group of the theory. Associated with any Lie group is the Lie algebra of group generators", etc. This despite the fact that gauge theory has a geometric character very similar to general relativity, and you can just as well describe general relativity in this relatively impenetrable way. You even frequently hear people saying explicitly that gravity is not like the other forces. So the answer to "how long would it have taken the general public to figure out that relativistic gravitation is about the geometry of spacetime, if not for Einstein?" may be "at least 108 years, if not forever".

Likewise I'm sure no one would ever say that special relativity is based on two postulates if not for Einstein, I doubt anyone would ever introduce it using trains, and the awful word "observer" might never have entered physics (though that's not really Einstein's fault—he used it in its ordinary vernacular sense, not the weird technical meaning that it somehow acquired later). On the other hand you don't hear much about his "general principle of relativity" these days. -- BenRG (talk) 19:25, 21 February 2013 (UTC)

This kind of thing is hard to prove conclusively - but if we look back to an era when new theories were not spread across the scientific community in a matter of days, there are many cases of similar breakthroughs being made completely independently. Calculus is a great example of that. Evolution is another. It seems that some level of 'background' math/science/data has to happen before it's possible for the next great thing to pop into someone's head - but once it does, someone will pick up on it in a matter of a few years. SteveBaker (talk) 20:14, 21 February 2013 (UTC)

Maxwell should have invented it. 23:04, 21 February 2013 (UTC) — Preceding unsigned comment added by Count Iblis (talk • contribs)

Average energy obtained for hydrolysis of a glycosidic bond and for a peptide bond

Anyone have a book or table which tells them what is the average energy obtained from hydrolysis of a glycosidic bond and also of a peptide bond? Many thanks, Kinkreet^{~♥moshi moshi♥~} 09:22, 21 February 2013 (UTC)

The change in enthalpy is often close to zero; entropic considerations will vary widely depending on the amount of water (free solution or crowded gel-like cell cytoplasm?), amount of product/starting material and steric considerations. 70.33.147.106 (talk) 02:28, 22 February 2013 (UTC)

pupae

Pupae found in Johannesburg Feb 2013

In Johannesburg, South Africa where i am currently on a holiday, the following pictures show what has been found on numerous walls. The pupae measure from 0.5 cm to 1 cm in length. I have been advised that a small black worm emerges from these and then will proceed to crawl up the wall pulling the shell or the pupae case with it. These are found usually at about head height or between 1.5 to 2 meters above the floor. I would please like your help in determining what this is. Thank you — Preceding unsigned comment added by Antonce (talk • contribs) 09:35, 21 February 2013 (UTC)

You will first need to upload the picture onto Wikipedia, or more preferably upload it somewhere else and provide a link to it. Simplying giving the pathway to the file on your computer does not actually allow us to see the picture. Kinkreet^{~♥moshi moshi♥~} 09:38, 21 February 2013 (UTC)

If what emerges is a larva, then this is an egg, not technically a pupa. See this similar thread on a South American bug. μηδείς (talk) 15:46, 21 February 2013 (UTC)

Materials that are compatible with the use and storage of chlorine pentafluoride, perchloryl fluoride, monomethylhydrazine, and diethylenetriamine?

Materials that are compatible with the use and storage of chlorine pentafluoride, perchloryl fluoride, monomethylhydrazine, and diethylenetriamine? — Preceding unsigned comment added by 192.248.248.55 (talk) 21:27, 21 February 2013 (UTC)

Building a rocket are we? Those are without exception very nasty chemicals without many uses, I don't think this is one the RefDesk should field. Fgf10 (talk) 22:00, 21 February 2013 (UTC)

Sorry, but Wikipedia is not censored. We do have a policy of not answering questions that require medical diagnosis or legal advice, but questions about nasty chemicals are allowed. (It may very well be that they shouldn't be allowed, but the way to do that is to change the policy).

192.248.248.55, start with reading the following articles (be sure to read the articles they link to as well): chlorine pentafluoride, perchloryl fluoride, monomethylhydrazine, and diethylenetriamine.

Then read Explosive material, Chemical explosive, Explosives safety, and Blast wave. Twice. Then decide on a safer propellant. One of the chemicals you list is a toxic gas, and one small leak will burn your skin and completely destroy your lungs. Not a nice way to die. --Guy Macon (talk) 04:17, 22 February 2013 (UTC)

What is the velocity of a body on a circular path?

Consider a body moving on a circular path, its direction of velocity is changing at every instant of time. Therefore, the velocity of the body is also changing at every instant, so, its an accelerated motion. Suppose, the body is moving on the circular path with a speed of 50km/hr. Then, what is the velocity of the body? - 50km/hr or zero. Don't forget the body is changing direction at every instant. Technologous (talk) 01:45, 22 February 2013 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Someguy1221 (talk) 01:51, 22 February 2013 (UTC)

I don't see this so much as a homework request as a philosophical misunderstanding. Velocity is a Euclidean vector, which is to say that it has a directional component as well as a magnitude. As you've noted, for the provided circumstance, the magnitude of the velocity (the speed) is 50 km/hr. At any given point in time, the direction is along a line tangent to the orbital path, oriented in the direction of travel. It's well-defined and is not at any point in the orbit zero, but neither is it accurate to describe the velocity as simply "50 km/hr" -- that's only a speed, because it lacks the direction. — Lomn 02:05, 22 February 2013 (UTC)

This is not my homework, you think this as my homework question because its answer is very simple. I asked this simple question because I was confused what would be the velocity of the body when it is changing direction continuously. Should we consider the direction while talking about velocity? Again, what would be the velocity of the body - 50km/hr or zero? Technologous (talk) 02:20, 22 February 2013 (UTC)

Neither. Velocity is defined as a Euclidean vector, and accurately stating it requires both a magnitude and a direction. 50km/hr is the magnitude of the velocity, as Lomn stated. The direction is changing at all times, but at any given moment is tangent to the circular path at the position of the body. Someguy1221 (talk) 02:25, 22 February 2013 (UTC)

It's usually simpler to just think of that as a constant rotational velocity. StuRat (talk) 04:56, 22 February 2013 (UTC)

how different are the different species of manatees?

Seems like there are 3 species, but not good breakdown of differences.

• are ranges at all touching? (do animals cross ocean to Africa or do West Indian ones come in contact with Amazon ones?

• physical differention?

• can they cross breed?

• any cpntroversy if the are really differnt species versus subspecies?

Fat burning zone

I've heard doing cardiovascular exercises at 65% of maximum heart rate burns most amount of fat. But there are lot of sources in google search saying fat burning zone is a myth. I was reading this source (page 2) which says fat oxidation is highest when exercising at 65% of MHR. It further claims during 85% of MHR exercise intensity, fat oxidation falls. On the other hand, this source claims during 65% of MHR intensity, a higher percentage of fat is burned, but at higher intensity, the total fat calories burned is higher. This contradicts the claim in the first source. Which claim is true? --PlanetEditor (talk) 04:43, 22 February 2013 (UTC)

Conditional Probability

I'm learning about probability in my statistics course, and I've learned that P(A|B) = P(A and B) / P(B). Similarly, P(B|A) = P(A and B) / P(A). Now, on a Venn Diagram, P(A|B) would be represented by the area that is within both circles as would P(B|A). However, if P(A) ≠ P(B) then P(A|B) ≠ P(B|A). If P(A|B) and P(B|A) represent the same area on a Venn Diagram, how can they ever be unequal? Have I understood some part here incorrectly? Lord Arador (talk) 04:51, 22 February 2013 (UTC)

I suggest you ask this Q at the Math Desk. StuRat (talk) 04:53, 22 February 2013 (UTC)

You have understood incorrectly. The area on the Venn Diagram that is part of both circles represents P(A and B). P(A|B) and P(B|A), on the other hand, are probabilities within a different set of possible outcomes, namely B and A, respectively. Someguy1221 (talk) 05:21, 22 February 2013 (UTC)

Alternate wheel arrangement

I've seem some carts, for laundry and such, which have wheels in an unusual diamond arrangement. Here's a top view:

+------------------+
|        □□        |
|                  |
|□□              □□|
|                  |
|        □□        |
+------------------+

1) What is the name of this arrangement ?

2) Do we have an article on it ?

3) What are the relative advantages and disadvantages of this arrangement ? StuRat (talk) 05:13, 22 February 2013 (UTC)

This site[31] might help. Unfortunately it doesn't name the arrangement. Dncsky (talk) 05:40, 22 February 2013 (UTC)

The website provided by Dncsky has the key to it but doesn't spell it out. The key is that when this layout is used, all 4 wheels are fixed, i.e., are not swivel castors, and the two centre wheels are installed slightly proud. This means that the cart sits with weight on the 2 centre wheels and only one end wheel - the other end wheel is clear of the floor by 5 to 10 mm. By applying minimal force, you can rock the cart transfer weight to the other end.

Disadvantage: As weight is only on 2 wheels when turning, the load carrying capacity is reduced by 50% compared to other 4-wheel arrangements.

Advantage: By pushing, the cart moves reliably in a straight line, but by a bit of up/down force you can get the weight off both ends simulataneously and easily turn the cart. Other layouts that permit turning will not stably follow a straight line when pushed along.

Advantage: Because it is symetrical, the cart is equally manuverable pushing or pulling from either end.

You most often see this layouts on carts used by the stocking staff in supermarkets, where a) the aisles are narrow and long, b) there's not much room for manuevering, and c) the weight carried is not great, due to retail packaging.

Wickwack 58.170.140.138 (talk) 06:42, 22 February 2013 (UTC)

Blast wave

How can I calculate the minimum "safe" distance from an explosion involving a known number of carloads of TNT? Thanks in advance! 24.23.196.85 (talk) 06:39, 22 February 2013 (UTC)