Wikipedia:Reference desk/Archives/Science/2012 May 13

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May 13

While I know that it's a myth that you can stop a moving car...

...by shooting a .44 Magnum round though the engine block (did that belief come from a line in the film Taxi Driver, or was it one of the Dirty Harry movies - that people just picked up on?), is there any handgun cartridge at all that can actually do this? --95.150.167.241 (talk) 00:16, 13 May 2012 (UTC)

Technically, a .44 Magnum round could stop a car according to the law of conservation of momentum. However, a 1000 kg vehicle could only be going .0051 meters per second if the bullet was fired from exactly the opposite direction. Similar calculations could be done with other cartridges. Reaper Eternal (talk) 00:23, 13 May 2012 (UTC)

I guess it all depends on what you mean by "stop a car". If you mean stop it's forward movement immediately, it would be have to be going very slow, as noted above. If you mean to stop the engine, I don't think you're likely to cause much damage to the engine block. You could take out any number of critical components by chance, however. The fuel line, distributor, ECM, any number of wires, etc., could stop the engine almost immediately. However, this requires a lucky shot. If you are content to stop the car eventually, putting a hole in the radiator gives you a much bigger target. StuRat (talk) 02:17, 13 May 2012 (UTC)

Stopping a car with any speed would require a serious amount of force, enough to interrupt oil flow probably, or as mentioned above a very lucky shot. Puncturing the radiator, as mentioned, will lead to the engine eventually seizing, but will not be any sort of rapid stop. the largest production handgun in the world is the .500 S&W, which produces a stunning 2600 or more foot-pounds of force. This is nearly 700 Ft-lbs more than the puissant .454 Casull. If you were to assume that the round is similar to the indenter used in a Brinell scale test, then against a typical grey cast iron engine block, it would make an indent defined by: Brinell hardness = (2*force in Kgf) / ((pi * diameter) * (Diameter - Sqrt(Diameter^2 -Indentation^2))) in this case that would be 260 = (2 * 35946.2) / ((Pi * 12.7)(12.7- Sqrt(12.7 - D))). This simplifies to: 260 = 71892.4 / 39.8 * (12.7 - Sqrt(12.7 -d)). The simple answer is 12.55mm which is almost exactly 1/2 in. (one half inch is 12.7mm as seen above). Since the engine block is greater than .5 in. thick, it's unlikely the handgun bullet would penetrate. Since cast iron is fairly ductile it is unlikely to shatter, and it's unlikely to deform greatly from that impact. Keep in mind this is a best-case scenario with a full-caliber tungsten penetrator, like a military AP round.Ssscienccce (talk) 10:24, 13 May 2012 (UTC)

Don't count on a cast iron engine block (leaving aside that most are aluminium alloy these day) not shattering. I've seen more than one engine block with a dirty great hole in the side caused by a thrown conrod (caused by either incorrectly installed bigend bolts, or the conrod itself breaking). However, engines can continue to run under such conditions, if the driver can stand the horrible noise. And if you are shooting at him, he will. Keit120.145.7.207 (talk) 12:29, 13 May 2012 (UTC)

HominidMachinae (talk) 06:42, 13 May 2012 (UTC)

Your best bet would be having the engine destroy itself, since a turning engine has a lot more kinetic power than a bullet. Breaking the timing belt or a valve (if a bullet can reach there) would do serious damage. A bullet at the right spot can initiate catastrophic failure, I suspect.  ::I would think that hitting the gearbox might well (though not always) cause immediate locking of the damaged gears and hence transmission, but you'd probably need quite advanced automotive experience to know where it was on your particular target, and whether or not it was effectively shielded from your position. {The poster formerly known as 87.81.230.195} 90.197.66.211 (talk) 11:31, 13 May 2012 (UTC)

Two words: smart bullet. Of course, when a bullet has the plans of every car coded inside it and decides where to hit in a few microseconds, the days of allowing the pathetic human behind it to have a say when it is fired will soon come to an end. Wnt (talk) 15:16, 13 May 2012 (UTC)

Mythbusters kinda hit on this one a while back. They were doing a myth about phonebooks making a car bulletproof... until Carrie put a .50 caliber round through the engine block(episode). So, I'd say no, a handgun won't be able to pull it off. — The Hand That Feeds You:^Bite 21:15, 13 May 2012 (UTC)

Like I said above, no handgun round could do it, even with military ammo. However a .50 BMG round from a rifle was BUILT to take out light armor would do it handily. Vehicles are tougher than a lot of people give them credit for. Anything capable of taking out a vehicle will be military-grade and probably a squad-level weapon (IE a Boys AT rifle is about the smallest they get, and that thing is 70 pounds). HominidMachinae (talk) 23:10, 13 May 2012 (UTC)

How's about a .50 BMG round fired from a pistol? I believe that .50 BMG pistols have been built before - though probably only in numbers amounting to single digits by people who want to see what holding and firing a .50 BMG pistol looks/feels like. --Kurt Shaped Box (talk) 19:19, 14 May 2012 (UTC)

The size of the round and powder charge is only part of the final end ballistic result, barrel length is also critical. a common pistol-length barrel firing a .50 BMG quite possibly would not have even burned all of its powder before said powder is flung from the barrel. a .500 S&W is about the upper end of "practical" pistol loads, though your definition of practicality may differ (the punishing recoil of the .500 S&W can break an inexpert user's wrist, or smash them in the face with their own weapon). If you put s shoulder-stock on the pistol you might fire a larger round, but then you're more properly talking about a carbine, and indeed that's what most rifle-round "pistols" like the .223 pistol are. HominidMachinae (talk) 04:36, 17 May 2012 (UTC)

Rusting after burning

Why is it that metal seems to rust much quicker after it's been burned in a fire? Or is this just confirmation bias on my part? Dismas|^(talk) 01:27, 13 May 2012 (UTC)

How is that you've observed the rusting of scorched metal often enough that you observed patterns in it?? If it is because you live in a city that was recently a battlefield, I sincerely feel for you, but otherwise, that is kind of strange. ike9898 (talk) 01:46, 13 May 2012 (UTC)

Upon reading the question I immediately thought of the old campers' dictum (now strongly discouraged) in my country, Australia, of what to do with empty cans - Burn, bash and bury. As Tin can tells us, "Tin cans are made of tinplate (tin-coated steel)", and the burning removed the thin protective tin coating, thus allowing the steel to rust more quickly. If this response has nothing to do with the question, just ignore me. HiLo48 (talk) 01:56, 13 May 2012 (UTC)

That seems like the proper explanation, although I doubt if the tin melts entirely. More likely there are just holes created in it. The plastic lining on the inside may burn away entirely, however, exposing the inside to the elements. Another factor to consider is that cans, once burnt, might be left in a fire pit, where they are far more exposed to the elements (water, changing temps, etc.), than the intact can was whilst in a cupboard. StuRat (talk) 02:06, 13 May 2012 (UTC)

My guess would be that it would have rusted before being exposed to high temperatures had there not been some coating on its surface preventing its exposure to oxygen and water. Paint serves this purpose but perhaps other clear substances, the presence of which one may not be aware of, could have been present before heating but removed or damaged by heat. Bus stop (talk) 02:29, 13 May 2012 (UTC)

No, I don't live in a war zone. And it occurred to me to ask after seeing the rubble from a house down the road that had recently burned down. Someone had made a pile of all the appliances and other large metal objects that were taken from the home. Every bit of it was rusted. Off the top of my head, I remember seeing a sink, a water heater, what appeared to be a washer or dryer, a stove, a few mattress springs, and what appeared to be possibly a table saw. Since the fire, it's been rather dry here with the exception being a couple days this past week and, of course more localized, the spray from the fire hoses. The items were all covered in rust. Dismas|^(talk) 03:34, 13 May 2012 (UTC)

Protective coatings burning off (like paint, oil on tools..) or damaged by impact, moisture for days, chemicals in the water, galvanic corrosion if touching other metals. Ssscienccce (talk) 10:51, 13 May 2012 (UTC)

You know what the difference between burning and rusting is? Speed. Apply oxygen to iron using water as a catalyst, and you get rust. Apply oxygen to iron using heat to speed up the reaction rate, and you get rust. The ingredients are the same, the underlying chemical reaction is the same, and the end product (iron oxide) is the same. --Carnildo (talk) 01:51, 16 May 2012 (UTC)

"Rusting" typically means the slow oxidation of iron, while "burning" can mean the rapid oxidation of anything (it also has other meanings), so there is so overlap, yes. StuRat (talk) 18:31, 18 May 2012 (UTC)

Autism

Autism is described as being on a spectrum. Presumably 'profound autism' is one end of that spectrum. What is the other end of the spectrum? 'Extrely Nuerotypical'? ike9898 (talk) 01:42, 13 May 2012 (UTC)

People who have abnormally good social skills. Count Iblis (talk) 02:08, 13 May 2012 (UTC)

Asperger's syndrome is a mild form of autism, and then there is PDD-NOS and high-functioning autism. StuRat (talk) 02:26, 13 May 2012 (UTC)

Stu is onto it. A basic definition of autism is the reduced ability to see another's point of view. But the range of Autism is not on a line - it is multidimensional. As with most mental/pschological "problems", a highly intelligent individual can overcome the "problem" by consciously thinking about it and correcting his behaviour. In doing so, the individual may make his autism seem different. I've put the word "problem" in quotes because to a high functioning autistic, it is a matter of opinion whether it is a problem. There are fields of employment where autism actually helps. Wickwack121.221.89.38 (talk) 03:08, 13 May 2012 (UTC)

'Stu is onto it' == 'Stu is on the autistic spectrum'? ~~ — Preceding unsigned comment added by OsmanRF34 (talk • contribs) 12:13, 13 May 2012 (UTC)

I'm sitting on a spectrum ? I can't feel it down there. I'd love to discuss this further, but it's 5:19, which means it's time for me to rip up pieces of paper for no apparent reason. :-) StuRat (talk) 05:19, 14 May 2012 (UTC)

Well, I wouldn't know, but as his posts are friendly, and he never attacks other posters, I doubt it. Note that I said "onto it", NOT "on it". The meaning is quite different. Wickwack58.164.226.214 (talk) 14:35, 13 May 2012 (UTC)

There is a hypothesis floating around by a Bernard J. Crespi that autism and schizophrenia are at opposite ends of a neurological spectrum. He's been going on about this since at least 2008. You can find lots and lots of papers [1][2][3][4][5] etc. about genes that affect both autism and schizophrenia. The problem is, it's hard to really categorize the effect as "same" or "different"; often one or the other is more what you'd call "altered". So some people paint it as two disorders based on the same mechanism, this fellow says they are opposite - in biology, there is little real distinction between synonyms and antonyms!

The most intriguing way to settle the issue would be to put some autistic kids on low-dose LSD - not enough to have obvious trippy effects, but maybe enough to revert autism to normality, if LSD is "psychotomimetic", and if that is some effect opposite to autism. But naturally many things could go wrong in such an experiment and some may question its ethics. ;) Wnt (talk) 04:38, 13 May 2012 (UTC)

You must be joking. Autism, neither the effects, not the cause, is well understood, but it is clear that it is caused by a lack of something - possibly a full set of functioning mirror neurons http://en.wikipedia.org/wiki/Mirror_neuron, maybe that and/or something else. You won't correct that with any sort of drug, any more than you could correct blindness, due say to genetically damaged retinas, with drugs. With enough LSD, you could maybe get the subject to think he has vision though... If you give LSD to autistic people, what you can only get is two problems instead of one - socially inept people who can't think straight, and if enough, socially inept people who halucinate and suffere from delusions. Hardly an improvement. Scientific American had a couple of good articles on autism, the mainstream professional view of it, and the role of mirror neurons, in the last year or so. Wickwack124.178.183.79 (talk) 11:07, 13 May 2012 (UTC)

I don't see the evidence that something is missing - while there are indeed large-scale and permanent variations in autistic brain (the location in the cortex where processing is done, the disruption of the inferior olive, AFAIR), it is often the case in biology that very visible alterations to an organ are less important than small and reversible regulatory changes. I'm not entirely serious in the sense that the low-dose LSD experiment I proposed probably wouldn't work and would very likely be regarded as unethical; nonetheless, I think there's a chance it would be beneficial. Wnt (talk) 15:11, 13 May 2012 (UTC)

In 2002 Simon Baron-Cohen put forward a theory that autism is an extreme form of the male brain, and there is a more recent article here about it. So one answer to the question could be "maleness" (or, depending on whether you see gender as a continuum, "femaleness").--TammyMoet (talk) 09:46, 13 May 2012 (UTC)

In the medical field generally, and the psycology field especially, you can always, if you look, find some wizzo professor who has very different and even bizare views about something. Here in Australia, we had a, otherwise quite well respected, medical professor who kept claiming that smoking had no role in lung cancer. He got in the news from time to time until he got lung cancer and died. However, TammyMoet's link is interesting. Wickwack124.178.183.79 (talk) 11:07, 13 May 2012 (UTC)

[OP] So, would it be safe to say that a spectrum is a bad analogy for the range of autism and related conditions?ike9898 (talk) 13:02, 13 May 2012 (UTC)

Not at all. "Spectrum" is a good word for it. Just as we talk about light having a spectrum, meaning a range of colours, autism is a spectrum, because it encompasses a range of conditions. Not only because you can be mildly, moderately, or severely autistic, but because not all autistic people, even if they are of the same severity, will display the same limitations or advantages. It is multidimensional in impact, as I said. (Not forgeting that autism can be a disadvantage or an advantage depending on the circumstances the autistic finds himself in). Wickwack58.164.226.214 (talk) 14:29, 13 May 2012 (UTC)

1 year.

Earth 2 forms a ring centered on the Sun, located on the circle* of old Earth's orbit. Earth 2 is stabilized by its rotational motion at old Earth's orbital speed. Your job is to find a way of having seasons on the ring. The idea for producing seasons is to allow Earth 2 to oscillate in the direction of its axis, perpendicular to the plane of its ring. Assume that a line from the Sun to Earth 2 oscillates through 46° of angle, with the mid-plane of the oscillation containing the Sun. What is period of the oscillations, in units of years?

If the Sun is a perpendicular distance $x$ from the ring, I worked out the magnitude of force acting on the ring to be ${\frac {Gm_{sun}m_{E2}x}{(r^{2}+x^{2})^{\frac {3}{2}}}}$ which is approximately ${\frac {Gm_{sun}m_{E2}x}{r^{3}}}$ since $r$ is surely much bigger than $x$. It follows that the "spring constant" is ${\frac {Gm_{sun}m_{E2}}{r^{3}}}$ and the period of oscillation is therefore ${\frac {2\pi }{\sqrt {\frac {Gm_{sun}}{r^{3}}}}}$. I look up the numbers and substitute and get a result of a single year. Since the result needs to be given in years, I am suspicious of this result and may have made a mistake. Does anyone agree/disagree with what I have done? --Widener (talk) 01:52, 13 May 2012 (UTC)

*By the way, I am aware that it is actually an ellipse.

Would not the "spring constant" be negative (which will not sustain oscillation)? Wickwack121.221.89.38 (talk) 02:41, 13 May 2012 (UTC)

That would be under the interpretation that $F=kx$ rather than $F=-kx$. Widener (talk) 03:06, 13 May 2012 (UTC)

If I'm understanding the question correctly, is it not obvious that it will be a year? I don't see why you need to use any maths. Egg Centric 02:43, 13 May 2012 (UTC)

Assuming I've understood his text etc correctly, he's visualising a donut/toriod shaped earth that supposedly oscillates up and down its rotation axis. The real earth has seasons because its rotation axis is at an angle away from perpendicular to its' orbital plane, forcing the seasons to be the same period as the orbital period. Such a thing is inapplicable to a donut surrounding the sun. So he needs to calculate the period of this "new" mode of oscillation, which is not locked to the orbital period. It will not actually oscillate though. Wickwack121.221.89.38 (talk) 02:50, 13 May 2012 (UTC)

I was going to say that the oscillation could be made any arbitary period (and therefore presumably a year) by altering the amplitude but then noticed the 46 degree thing... I see the problem Egg Centric 16:13, 13 May 2012 (UTC)

(So presumably you don't want to model it as a ring, just model it as a point mass with a centre of gravity which happens to pass through the sun during the oscillation, which means the equations will be very simple. Although it's a decade since I've done any mechanics, as this thought probably demonstrates) Egg Centric 16:15, 13 May 2012 (UTC)

The statement that r is much bigger than x is not valid. It's bigger, but not enough bigger to make the approximation valid. The max value of x/r is tangent(23 degrees), which is about 0.42. Looie496 (talk) 03:07, 13 May 2012 (UTC)

I don't think this will actually work - the varying distance from the ring to the Sun means the idea of stabilising it by having it revolve at orbital speed doesn't work. The centripetal force from the Sun's gravity won't balance the centrifugal force from the revolution, since the revolution is constant and the relevant component of the Sun's gravity isn't. That means you're going to get internal forces within the ring, which will rip it apart (unless it is made of some hypothetical super-strong material). --Tango (talk) 19:32, 13 May 2012 (UTC)

I don't know what "stabilized" means here; rotation doesn't affect the tendency of a Ringworld to drift into the sun. —Tamfang (talk) 03:20, 14 May 2012 (UTC)

By the way, this sounds like a homework question to me, presumably for calculus class. Ah well, too late now. ;) Indeed, the Ringworld is unstable, but only small attitude jets are said to be necessary. The oscillation along the axis would be unrelated to its instability from side to side.

As for the question, the Ringworld is simply a vertical wall to hold its bits in place. Mass cancels out and is irrelevant. A particle of the ring is accelerated toward the sun at G m_sun/sqrt(x²+r_earth²), but toward the midline at that multiplied by x/sqrt(x²+r_earth²). So you have to integrate dx/dt for G m_sun x/(x²+r_earth²), I think... And I don't think that you can assume x is much smaller than r_earth, or else you wouldn't get seasons from it. Besides, knowing/looking up/figuring out this integral is presumably the point of the assignment. ;) Wnt (talk) 04:30, 14 May 2012 (UTC)

Its not likely to be homework, becasue as such it would be a trick question - its not solvable because it is not oscillatory. In any case, its ok, because this OP showed us he had a go at working it out. Wickwack124.178.138.77 (talk) 06:02, 14 May 2012 (UTC)

If it doesn't oscillate, what does it do? It's not an escape trajectory (you can imagine it starting at rest at one of the mid-winter/mid-summer positions, so the total energy must be negative), and there isn't enough going on for it to be on a bounded but non-periodic trajectory (it essentially boils down to a two-body problem). It's not quite simple harmonic motion (the restoring force is inverse square, rather than a simple linear force) but it's still an oscillation. --Tango (talk) 18:24, 14 May 2012 (UTC)

It is an escape trajectory, as the "restoring force" for oscillation perpendicular to the rotation axis is negative. Unless I've mis-understood the OP's question. Please re-read the original question, my third post (begins "assuming I've understood....". and then tell us what you think. Your previous posts (and possible EggCentric's) are sort of/partly consistent with a different interpretation - that of a toriod (or bottomless & topless thin drum) with its centre of gravity in eliptic orbit about the sun. That will give seasons, but is not consistent with the OP's explanatory words to his question. Wickwack120.145.187.143 (talk) 00:54, 15 May 2012 (UTC)

I agree with Tango that you have misunderstood the question. The idea is that you have a ring, with the sun at the center, then you give it an "upward" push. It slows down until the angle of the face of the ring and the sun is 23 degrees, then accelerates back "downwards" until it reaches the ecliptic again and starts decelerating, then at -23 degrees it accelerates "upward" again. I think you've gotten lost in the equations, because it's simple to see that it will be an oscillator if you look at the problem practically :)

And to the OP: As a rough check of your calculations, you could take the freefall time of a point mass with the same mass as the ring at an equivalent distance directly above the sun, then quadruple it to get the time for a full oscillation. Too lazy to do the calculations myself, but a quick back-of-the-envelope calculation tells me the oscillation period should be on the order of hours-days, not years. -RunningOnBrains^(talk) 03:53, 15 May 2012 (UTC)

Agreed. I think Wickwack is reliving the glory days of (Larry Niven says, MIT students chanting "The Ringworld is unstable". But here the Ringworld is being pushed perpendicular to the direction it was moving in Ringworld Engineers. Wnt (talk) 19:39, 15 May 2012 (UTC)

Unfortunately no glory days. I've had another think, prompted by Runningonbrains's method, and decided that it will oscillate after all. Wickwack124.178.42.68 (talk) 01:03, 16 May 2012 (UTC)

Why is CO not the anhydride of formic acid?

The acid's article does not describe why formic acid behaves differently from carbonic acid, which I viewed as simply a higher oxyacid of carbon.--Jasper Deng (talk) 03:30, 13 May 2012 (UTC)

I think you might be mis-reading how carbonic acid behaves when it dehydates: its reaction is O=C(OH)₂→O=C=O, which is a standard gem-diol dehydration to form a carbonyl (lose an H from the OH, O remains attached). Formic acid doesn't have a gem-diol, and forming CO from it would involve loss of H from the C itself. It's pretty difficult to envision losing H and OH from the same position and getting anything close to a stable structure in general: dehydrohalogenation from a single atom (R₂C(H)(X)→R₂C analogous to your O=C(H)(OH) proposal) gives a carbene, which is generally extremely unstable unless there is something special about the R groups.

On the other hand, carbon monoxide is an anhydride of formic acid (see our formic anhydride article for details about CO formation in this sense). The carbene-like structure for O=C: in particular is just a resonance form of carbon monoxide, and the lone-pair on the "carbonyl oxygen" is exactly special to fix the octet instability of this carbene. DMacks (talk) 03:48, 13 May 2012 (UTC)

My conclusion stemmed from the fact that CO itself does not seem to hydrolyze in a reaction like CO(g) + H₂O(l)→ H₂CO₂ analogous to carbonic acid.--Jasper Deng (talk) 03:56, 13 May 2012 (UTC)

Carbon monoxide does react with water, just not in the way your intuition thinks it does. See Water gas shift reaction. --Jayron32 04:11, 13 May 2012 (UTC)

I knew about that particular one... I guess that there's little reason for my previous predicted reaction? -Jasper Deng (talk) 04:13, 13 May 2012 (UTC)

(edit conflict) Formic acid is the first of a homologous series known as the carboxylic acids, and those form dimeric anhydrides. If you look at formic acid like acetic acid and propionic acid, you'll see the pattern. The oxidation state of carbon in all three of those is the same, whereas in the carbonate ion, the electronics are quite different. Another way to think of formic acid as quite different than carbonic acid: formic acid has one of its hydrogens bonded directly to carbon, whereas all of the hydrogens in carbonic acid are oxygen bound. Any of these ways of thinking of it will lead you to the more correct conclusions than you reached. --Jayron32 03:50, 13 May 2012 (UTC)

Sorta the same reason that phosphorous acid is diprotic while phosphoric acid is triprotic, I guess...--Jasper Deng (talk) 03:56, 13 May 2012 (UTC)

Have you looked at carbonous acid and methanediol? Plasmic Physics (talk) 07:03, 13 May 2012 (UTC)

Formic acid was once made at a large scale by dissolving CO in hot NaOH solution under pressure. So you could consider it to have some anhydride properties (stoichiometrically) Staticd (talk) 12:17, 13 May 2012 (UTC)

Are there any traits (genetic traits) that are only inherited from one parent?(mom or dad)

Like the mitochondrial DNA that is inherited only from mothers?--2.147.67.209 (talk) 06:43, 13 May 2012 (UTC)

Anything on the Y chromosome is inherited from the father. Boys only, of course. — kwami (talk) 07:53, 13 May 2012 (UTC)

Colour-blindness in boys comes via the mothers. There are others, but I can't remember them right now. HiLo48 (talk) 08:29, 13 May 2012 (UTC)

Yes, the mitochondrial DNA is only inherited from the mother. Since virtually everything inside that DNA is directly related to the function of mitochondria, you don't really see anything but diseases being passed in it (i.e. when it works, you don't notice, except that you're not sick/dead). See Mitochondrial disease for a list of potentially inherited traits. As mentioned above, the Y chromosome is only inherited from the father. Explaining what HiLo said, boys inherit their X chromosome only from their mother. Sex linkage lists a variety of diseases that are linked to the X chromosome. There is also the case of genomic imprinting, in which case you inherit the DNA from both parents, but the DNA from only one parent is active and determines the phenotype. There are maybe 90 such genes, spread out across the chromosomes. Someguy1221 (talk) 08:46, 13 May 2012 (UTC)

Greenland as three islands

There's been a problem with an unref'd or poorly ref'd assertion at Greenland for several years now. The common understanding is that Greenland is really three islands connected by ice. A look at a topographic map shows that's not true: the center is below sea level, but the rim is unbroken. However, AFAIK that's not where the story came from. If the ice sheet were to melt completely, the sea level would rise 6–7 m, and then Greenland would be three islands; conversely, it's thought that glaciation united what had been three islands (at a higher sea level than now). I can't find a decent ref, though. Does anyone know of one, or am I remembering it wrong? (I can find lots of maps of what Florida would look like if the Greenland icecap were to melt, just not what Greenland would look like.) — kwami (talk) 07:52, 13 May 2012 (UTC)

Another theory is that as the icecaps melt, the weight removed would allow the land to rise, so none of Greenland without icecap may be below sea level. HiLo48 (talk) 08:27, 13 May 2012 (UTC)

Not a "theory" but a well-known phenomenon. It's pretty slow, though. Short Brigade Harvester Boris (talk) 21:24, 13 May 2012 (UTC)

I traced the assertion back to 1951 - see the reference I added to the article. However, the original discoverers said nothing about sea level rise so I deleted that bit. --Heron (talk) 09:56, 13 May 2012 (UTC)

check out greenland geology map186.151.67.249 (talk) 11:18, 13 May 2012 (UTC)

OK, you write the article and then we'll check it out. -- ♬ Jack of Oz ♬ ^{[your turn]} 21:39, 13 May 2012 (UTC)

Canada & the northern US are still rebounding from the retreat of the glaciers 11 ka, so I think it might be a while before the same happens to Greenland.

Without a rise in sea level, it looks as though Greenland would be a single island with a giant lake in the middle. But that's not realistic: all that water has to go somewhere. The 1951 claim may not have addressed that, but it's been done since. — kwami (talk) 03:01, 14 May 2012 (UTC)

And to further complicate matters, consider that the warmer conditions needed to melt the Greenland ice cap would also melt the ice shelves off Antarctica, some mainland Antarctic glaciers, and some other smaller glaciers. So, should that extra sea level rise also be taken into account ? If so, perhaps Greenland would be fully submerged. StuRat (talk) 04:51, 14 May 2012 (UTC)

No, that would not happen even if the entire planet were ice-free. But correlations with Antarctica are speculative, and you could at least hypothesize that only the northern hemisphere would be affected, as a minimal model. Not likely, but if Greenland melts, the sea level must rise by at least the amount of melt water from Greenland, so that's the theoretical lower bound. — kwami (talk) 11:09, 14 May 2012 (UTC)

I have a hard time imagining and scenario where only the Northern Hemisphere warms up. StuRat (talk) 23:33, 14 May 2012 (UTC)

Some kind of giant hat, perhaps? FiggyBee (talk) 13:27, 15 May 2012 (UTC)

I suppose if Greenland drifted south that might have the same effect, although the tens of millions of years for this to happen by continental drift is vastly longer than the glaciation cycles, which are on the order of tens of thousands of years. StuRat (talk) 17:02, 15 May 2012 (UTC)

Well yeah, but again, it's the bare minimum: if Greenland is icefree, the sea-level rise will be 7m plus whatever from Antarctica, so 7+m. The amount of the "+" is unknown, really, so I was going with 7m. But it's not enough. Got a data set from the NSIDC and mapped Greenland for various sea-level rises. In order to get the inland basin to connect at all, you have to raise sea levels almost 50m. That opens up the northwest channel (or channels, really: there are two of them). To get a second channel for Greenland to break up, you need close to the 68.3m estimated rise from both Greenland and Antarctica, and even then it's a rather narrow channel. Thermal expansion would push that up, but unless that's a big difference, the northeast channel would not open, so at most Greenland would be two big islands. — kwami (talk) 23:31, 17 May 2012 (UTC)

The Nature of Jupiter's Metallic Hydrogen Interior

The wikipedia article of Jupiter says that most of the interior is Metallic hydrogen a kind of degenerate matter. What I'm not clear on is how solid this state of matter would be. Does the metallic hydrogen act more like a liquid or a solid or a gas? Ignoring the gravitational effects, could a spaceship fly through it? I've always been under the impression that Jupiter was mostly a cloud of gas and now need to revise my incorrect ideas. Thanks for any help. --CGPGrey (talk) 10:15, 13 May 2012 (UTC)

It says that in the Jupiter article that there is liquid metallic hydrogen; a spaceship cannot fly through the centre of Jupiter; it is not simply a cloud of gas. Plasmic Physics (talk) 10:31, 13 May 2012 (UTC)

It is a planet with a ferrosilicate core, with a mantle of liquid metallic hydrogen, overlaid with a deep ocean of super-critical molecular hydrogen, topped off with a thick atmosphere of various gasses. Plasmic Physics (talk) 10:45, 13 May 2012 (UTC)

To get hydrogen solid, it would need to be below the triple point temperature, which is only 13.84 K. Not very likely within a large planet. Keit120.145.7.207 (talk) 12:21, 13 May 2012 (UTC)

But as the pressure on the hydrogen increases, so does its melting point. Conceivably, the pressure inside Jupiter could be high enough for solid metallic hydrogen to exist near the core. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 12:40, 13 May 2012 (UTC)

The triple point is where all three phases can exist. Maybe you mean the critical point. But that's thepoint where there's no more difference betweengas and liquid. Higher pressure may still make it a solid. Ssscienccce (talk) 12:55, 13 May 2012 (UTC)

I meant the triple point. Whoop whoop could be correct if the melt line, which begins at the triple point, "leans" significantly towards higher temperatures at higher pressures. From memory, there's not a lot of lean in the hydrogen melt line, but I don't have a phase diagram for hydrogen to hand. Keit120.145.7.207 (talk) 14:21, 13 May 2012 (UTC)

There are some conflicting statements in the metalic hydrogen article imo:

• The initial prediction about the amount of pressure needed was eventually proven to be too low.
• Because previous predictions of the nature of those interiors had taken for granted metallization at a higher pressure than the one at which we now know it to happen, those predictions must now be adjusted.
• at 345 GPa, hydrogen is still not a true alkali metal
• at 140 GPa ... the hydrogen might be considered metallic.
• The lead mentions solid metallic hydrogen but the rest of the article seems to talk about liquid only. It's a bit confusing Ssscienccce (talk) 12:55, 13 May 2012 (UTC)

Even if it's a gas, that doesn't mean a spaceship could fly through it. The density would be enormous, which means the resistance would be enormous too. It would take lots of energy to move the spaceship and all that energy would go into generating heat, so the spaceship would either not move or it would burn up. --Tango (talk) 20:03, 13 May 2012 (UTC)

There is a possibility that metallic hydrogen could be metastable at low pressures. Then if a giant Jupiter like planet is destroyed in a collison, there could be small fragments containing metastable metallic hydrogen, which could give rise to strange meteorites, see here. Count Iblis (talk) 20:54, 13 May 2012 (UTC)

Interesting idea, what would happen if such a meteorite, composed of solid metallic hydrogen, entered Earth's atmosphere? Could it perhaps be a candidate for the Tunguska event? Plasmic Physics (talk) 00:43, 14 May 2012 (UTC)

Maybe a reson why it could descend so far into the atmosphere, could be that the hydrogen centre was thermally insulated by another frozen gas such carbon dioxide (not likely). Plasmic Physics (talk) 00:48, 14 May 2012 (UTC)

I don't think you can have metallic hydrogen at any temperature if the pressure is not something "astronomical" - and by that I mean more astronomical than a meteorite. ;) Besides, I think if you work it out you'll find a meteorite contains more energy in its motion than it would have in chemical energy even if it were hydrogen ... but I don't know for sure. Anyone up for an exercise? ;) Wnt (talk) 19:37, 15 May 2012 (UTC)

Stronger superacids than fluoroantimonic acid

Since gold pentafluoride and bismuth pentafluoride are both stronger fluoride-ion acceptors than antimony pentafluoride, shouldn't hexafluoroauric acid, HAuF₆, and hexafluorobismuthic acid, HBiF₆, be even stronger superacids than fluoroantimonic acid? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 12:15, 13 May 2012 (UTC)

I think these superacids are in the Brønsted–Lowry sense, so acidity is "how strongly does the metal–F complex hold the H" not "how strongly does the metal hold the F?". AuF₅ might be the strongest Lewis acid, since that deals with electron-acceptor modes of the metal center. But adding HF to AuF₅ causes the whole thing to decompose--due to that acidity--and liberate fluorine and gold(III) fluoride (see [[doi:10.1002/1521-3773(20011001)40:19<3690::AID-ANIE3690>3.0.CO;2-5]]) rather than forming a [AuF₆]^– cluster. I know this exact question has been asked on WP before but I can't find it right now. DMacks (talk) 15:47, 13 May 2012 (UTC)

Heh...was my talk-page. See User talk:DMacks/Archive 13#Need help from the smarter where I had found some refs and related ideas. DMacks (talk) 20:40, 13 May 2012 (UTC)

Steel laptop and electroshock

How do they isolate the steel of those new laptops so you don't get a shock? OsmanRF34 (talk) 12:51, 13 May 2012 (UTC)

I don't think there are any steel laptops, although some are made from aluminium or titanium alloys. They are isolated in the same way as any other electricity-using equipment with metal part (washing machines, cars, stereos, toasters...), namely by making sure that there is no electrical contact from power carrying circuits to the frame of the device. If you want more details, iFixit has an article on disassembling a unibody MacBook Pro with pictures showing how the components are mounted on plastic circuit boards mounted inside the metal unibody enclosure. --Stephan Schulz (talk) 13:42, 13 May 2012 (UTC)

In countries following European standards, and countries that have their own standards more or less in harmony with European standards, laptops and any other appliance mus conform to one or two choices. With Choice 1, any and all exposed meatl work must be electrically earthed. The 'third pin' (the one that is different to the other two, or is aligned different to the other two) on the power plug carries the earth connection. Should any fault occur which would otherwise make the exposed metal live, the current is carried away via the earth connection, so you can't get a shock. With Choice 2, the laptop or appliance must conform to the standard commonly known as "double insulated", and must display the double insulated symbol (two squares, one inside the other). In double insulated equipment, it is designed in such a way that no concievable fault can, on is own, cause the exposed metal work to become live. This may be achieved by simply providing two insulating barriers, or by other technically acceptable methods. Choice 1 is the most common choice for personal computers & laptops. As a general rule, countries that have only 2-pin wall outlets (eg Japan) historically had lower electrical standards. However, these days, as manufacturing is for world markets, equipment is made to conform to European standards. Keit120.145.7.207 (talk) 14:12, 13 May 2012 (UTC)

Further to the above valid replies, all the laptops that I have ever seen in the last fifteen years run from a low voltage (usually 19v) fed from a "power brick" (Switched-mode power supply) which conforms to the EU double-insulation standards in isolating the whole of the laptop from any high voltages. Dbfirs 15:08, 13 May 2012 (UTC)

I think Dbfirs' answer is actually the most relevant one here. It is the power adapter that will have to comply to the mains standard, not the laptop, the laptop runs on relatively low voltage DC. The metal on the laptop does not need to be earthed externally as it is not a shock hazard. Vespine (talk) 22:53, 13 May 2012 (UTC)

Not all laptops have external power units. All the laptops (Toshibas mostly) they issued us with at work had internal power supplies. Wickwack121.215.40.247 (talk) 00:42, 14 May 2012 (UTC)

Ah, I wondered if they existed. I was trying to remember whether my first work laptop (heavy and bought in the 1980s) had an internal supply. I assume they conform to the same double-insulation regulations, rather than have all metal earthed. Dbfirs 07:23, 14 May 2012 (UTC)

Nope. Those Toshiba laptops were earthed via the third pin, the same as a desktop PC. Wickwack60.230.232.194 (talk) 07:52, 14 May 2012 (UTC)

Was this perhaps a few years ago? I first looked at the available models at the Toshiba site, but had to expand my search a bit to find one: a Toshiba t5200 from 1988, 8.5 kg, with built-in power supply. Who would have thought that the first laptops didn't run on batteries... Ssscienccce (talk) 11:20, 14 May 2012 (UTC)

Promiscuity and inbreeding

Would a fully promiscuous mating system reduce the minimum starting population needed to avoid problems related to inbreeding? Assuming equal gender ratios in the starting population. Horselover Frost (talk · edits) 16:31, 13 May 2012 (UTC)

As compared to a monogamous mating system, I mean. Horselover Frost (talk · edits) 16:32, 13 May 2012 (UTC)

A fully promiscuous mating system would make the problem worse, not better, since it would imply some level of mating between close relatives. But if you didn't really mean that, then I think the answer is that it would not make any difference, since every child has precisely two parents regardless of how promiscuous the mating is. Looie496 (talk) 18:21, 13 May 2012 (UTC)

a system of non-random mate choice for dissimilar individuals would be the best defence against inbreeding in a small population. (rats can smell out close relatives and some plants reject closely related pollen from fertilizing their eggs). Here are my calculations for a random mate choice system -

• monogamy with random partner: If an individual has 'n' offspring, probability of all n being inbred = probability of picking a close relative (p)
• promiscous mating with random partners: probability of all n being inbred = probability of picking a close relative n times = pⁿ < p for n > 1.

So yes, by my rough calculations for a toy model promiscuity is better than monogamy for inbreeding.Staticd (talk) 19:09, 13 May 2012 (UTC)

What do you mean by "problems related to inbreeding", or "fully promiscuous"? There are many separate issues at play in inbreeding, and not all of them are necessarily detrimental to the population. In the meantime, you may be interested in founder effects, and assortative mating. SemanticMantis (talk) 19:51, 13 May 2012 (UTC)

Lead poisoning and weight gain

Could children's bodies react to lead poisoning with weight gain--to sequester the harmful lead in fat tissue?Rich (talk) 19:54, 13 May 2012 (UTC)

I doubt it, since the article mentions as classic signs and symptoms in children: loss of appetite, abdominal pain, vomiting, weight loss. Ssscienccce (talk) 21:35, 13 May 2012 (UTC)

What you're talking about is an evolutionary response. Those only occur in response to problems which remain a serious threat to the species for thousands of generations. Thus, we have evolved a starvation response to keep us alive during famines. However, toxic lead exposure is rare today, and almost unheard of throughout most of human history. That's just not enough of a threat to the species to cause such an evolutionary response. StuRat (talk) 04:57, 14 May 2012 (UTC)

Stu, if by "toxic lead exposure", you mean exposure high enough to produce obvious symptoms, then its true that such exposure isn't common. However, lead is toxic, meaning degradation in rational behavior and measurable degradation in intelligence, down to very low levels. In response to another question, somebody posted a link to a study that showed that blood levels in US children had dropped in recent years. However, in western countries generally, lead is ubiquitous in the environment, resulting in blood levels around 30 to 100 ug/L. The USA has set an arbitary limit of 100 ug/L as safe, but that is not universally accepted - some experts think that is too high. Even so, a significant fraction of childen are above the US limit. It only takes a few industrial incidents or lead-using industry not complying with requirments, or some developer turning old industrial estates into residential, and you get children way over 100 ug/L. Here in Australia, lead poisoning of children gets reported in the media from time to time. See example report http://www.esperanceport.com.au/downloads/inquiry/Leadissueupdate2.pdf Wickwack124.178.138.77 (talk) 05:55, 14 May 2012 (UTC)

But evolution doesn't care about low-level exposure (please, no comments on my anthropomorphization of evolution). It would only care if a large percentage of people were prevented from reproduction, due to lead exposure. StuRat (talk) 23:30, 14 May 2012 (UTC)

Correct. Low level exposure to lead reduces your intelligence, but it doesn't take much brains to get a girl pregnant. Wickwack120.145.187.143 (talk) 01:02, 15 May 2012 (UTC)

I dunno about "toxic lead exposure is [...] almost unheard of throughout most of human history". Lead has a long history of all kinds of uses in western civilization, and it has been suggested (controversially) that sapa made in lead pots was a contributing factor in the decline of the Roman empire. Better documented, back to ancient Greece, is illness among miners, plumbers and potters who worked with lead. In the medieval and early modern period there were frequent outbreaks of illness caused by alcoholic drinks made with lead equipment or sweetened with lead (Devon colic). Of course, I agree with the rest of your assessment. :) FiggyBee (talk) 22:47, 14 May 2012 (UTC)

thd

what total harmonic analyzer measures? — Preceding unsigned comment added by Vivekmishra1988 (talk • contribs) 20:05, 13 May 2012 (UTC)

Total harmonic distortion. Tevildo (talk) 20:12, 13 May 2012 (UTC)

And THD analyzer. Red Act (talk) 20:17, 13 May 2012 (UTC)

How does myopia work?

I'm wondering how shortsightedness can work: apparently it is usually due to the eyeball being too long, but the point as I see it is that the lens focuses the image so that it will land on the retina. I can't see why we treat it as a focal-length mismatch between the eye and the lens, when the lens is adjustable. It does not have a fixed focal length, so what is the problem? Why can't it just compensate?

Another question: why do people's eyes so frequently get worse? Why don't they spontaneously get better? Assuming the eye is fixed in size and shape from one's early years, what is actually changing to make shortsightedness worsen, and why does it not improve? Thanks in advance, IBE (talk) 20:24, 13 May 2012 (UTC)

It does compensate, which is why they can still see things that are nearby. There is a limit to the range of focal lengths the lens can produce, though. Normally, that limit allows objects at distances from a few centimetres to infinity to be in focus. For shortsighted people, the range doesn't go all the way to infinity. For longsighted people, it starts further away. Some people (particularly the elderly) have both, so end up with a very short range - this can be corrected with bifocals. --Tango (talk) 20:45, 13 May 2012 (UTC)

The lens and the cornea, in combination, focus the light to a particular point. If you have normal vision, the image lands in the right place on the retina. If the eyeball is slightly misshapen, the focused image does not land in the right place. As Tango says, your eyes can adjust, but only so much - and their ability to adjust decreases with age. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:10, 13 May 2012 (UTC)

I think the reason why eyes get worse with age is that our ability to change the focus decreases, as a normal part of aging. There is sometimes an improvement in vision, such as in middle age, when people tend to go from having myopia to presbyopia. This can result in a short window when vision is improved. Eye exercises might also improve vision, at least temporarily. StuRat (talk) 05:04, 14 May 2012 (UTC)

Presbyopia unfortunately cannot help myopia: myopia occurs when the longest focal length is too short (principally a function of the cornea and eye length), and presbyopia is the lengthening of the shortest focal length without affecting the longest (because it is the ability of the crystalline lens to shorten the focal length of the cornea that is reduced). Put differently, presbyopia reduces a sort of depth of field of the eye, rendering some distances impossible to focus on without granting any other focusable distances in exchange. --Tardis (talk) 01:22, 16 May 2012 (UTC)

Myopia may be caused partly by doing to much near work, or for example children that read a lot and keep the book close to their face. The ciliary muscle is a ring of smooth muscle around the lens. When the muscle s relaxed, the lens is stretched (flattened) by the zonule fibers that connect to the ciliary muscle. When the muscle contracts, the ring gets smaller, there's less stretching so the lens becomes more spherical. How this would explain myopia is not certain, it seems there are several theories. Some researchers suggest myopic people use reading glasses (+ dioptry) for near work. Now the opposite usually happens, children get perscription glasses when they can't read the blackboard in class, and they keep them on when reading and writing. To focus correctly, the ciliary muscle will have to contract even more in that situation. But we don't know for sure. It's not clear why myopia doesn't worsen as rapidly with contact lenses as with glasses for example. Ssscienccce (talk) 12:29, 14 May 2012 (UTC)

what is cally disease

got it off of a mate and has same symtoms — Preceding unsigned comment added by Errrrrrcally (talk • contribs) 20:54, 13 May 2012 (UTC)

See a doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:04, 13 May 2012 (UTC)

Cally disease is a disease from the planet Auron, in the TV fiction Blake's 7. Has someone pulled your leg or are you pulling ours? Wickwack121.215.40.247 (talk) 00:37, 14 May 2012 (UTC)

Maybe that's what his unstated symptom is: A pulled leg. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:22, 14 May 2012 (UTC)