Wikipedia:Reference desk/Archives/Science/2007 October 31

From Wikipedia, the free encyclopedia

< Wikipedia:Reference desk | Archives | Science

Science desk
< October 30	<< Oct \| October \| Dec >>	November 1 >

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

[edit] October 31

[edit] Running hands under Superacid

After reading Superacids, what would happen if someone washed their hands under a tap of fluoroantimonic acid? How fast would the hands disintegrate? Acceptable 01:35, 31 October 2007 (UTC)

I guess it is unacceptable to post chromic acid stories? Delmlsfan 01:51, 31 October 2007 (UTC)

I once breathed in fumes of hydrogen chloride gas (by accident), not a very fun experience... -- MacAddct1984 14:02, 31 October 2007 (UTC)

Once it hits the water of your hand, it's no longer nearly as super. That is, it becomes little different than a really really concentrated solution of other acids (hydrochloric, sulfuric, etc) in regards to its acid effects. On the other hand (sorry:) the fluoro and stibbic components might present other hazards all their own. DMacks 02:01, 31 October 2007 (UTC)

[edit] Transporting rice

Car Talk's most recent puzzler was something along the lines of:

With old wooden ships, what common household item, if not stored properly, would sink a ship in a matter of minutes?

Apparently rice was the answer. If it wasn't stored properly and got wet, the massive amounts of densely packed rice would swell and split the ship apart. Has anyone heard of this before? It certainly sounds plausible. -- MacAddct1984 01:42, 31 October 2007 (UTC)

Car Talk got this information from the book Tall Ships by Philip McCutchan.[1] The author’s name is misspelled on Car Talk’s web site.[2] That book says "Spaced along the upper deck were the cargo hatches with their heavy covers of reinforced hardwood planks, well chocked in and secured with three separate layers of tarpaulin, held down with ropes and more chocks to withstand the pounding of heavy seas. Below the hatches lay the reason for the ship's presence on the sea, her cargo, to be held inviolate against nature and disaster, against fire that could come from a self-combustible cargo like wool, or a cargo that could swell when it met water, such as rice, which on more than one occasion in the long story of the sea swelled and in its irresistible pressure split the sides of holds like paper and sank those ships in minutes."

But that’s just what Philip McCutchan said. From the British shipping act in 1875, it sounds like the primary concern about properly storing grain on ships at the time was actually that the ship could sink if the grain shifted.[3] Maybe this is a question for MythBusters. MrRedact 03:25, 31 October 2007 (UTC)

I guess what bothers me about this is that once the water gets at the outer regions of the rice cargo, that will start to swell and the pressure build-up ought to lock out the water from getting in much further. But a lot depends on how fast the water is getting in and how fast rice swells. I guess it could be true. Definitely a good one for Mythbusters though. Car Talk's puzzlers are not exactly reliable sources of information! SteveBaker 03:32, 31 October 2007 (UTC)

This was a plot in a Horatio Hornblower book. He lost a prize of war. The ship was sinking even though no water was in the "well". It gains weight as well as stressing the hull. --DHeyward 05:18, 31 October 2007 (UTC)

For the locking question, I think osmotic pressure will keep sucking the water in to the center until they are all equally saturated. A dry rice grain next to water saturated one will suck the water out of it. --DHeyward 05:21, 31 October 2007 (UTC)

DHeyward: that was not a book, but rather the second chapter of Mr. Midshipman Hornblower. Algebraist 21:08, 31 October 2007 (UTC)

[edit] Children's vs Adult's voices

What are the differences between children's and adult's voices, excepting the obvious physiological effects of growth and hormonal adjustments?
For example, children's voices tend to sound more sing-songy, breathy, and rhymical, but have there been any studies to make quantitative or qualitative measures of the difference in voice-qualities as age progresses?
It is obvious that human's are readily able to differentiate between younger and older speakers independently of any use of linguistic cues : are computers able to do the same, and under what heuristics would they operate?
Are there any posited hypotheses of the cognitive causes of these non-physiologically determined variations?

Many thanks 81.153.3.36 10:05, 31 October 2007 (UTC)

I think this belongs in the section on Language and Linguistics. Meanwhile, I'm not well studied at all in developmental linguistics, but I can try to answer with what I know.

Obviously, as you stated, as a child gets older his larynx expands and produces deeper tones as the vocal chords vibrate. Similar resonance differences occur as the size of the oral and nasal cavity expand. However, the prosodic changes (those in rhythm and tone) can probably be traced to what are still not well understood phenomena in child linguistics. For example, a toddler will show reduplication (repetition of words) and other types of word play, depending on age, as he learns to speak. He will also exaggerate and misuse intonation (the parents do this too when they speak to children for the precise reason that intonation is difficult to master). All of this is most likely a result of the problem of learning something as complicated as language simply from cues around you. Computational models of this type of learning are very simplistic, last I've seen, and usually involve limited degrees of freedom (such as a simple robot learning to walk or play the drums according to outside information). None that I know of are linguistic in nature.

It is true that the age of a speaker can be approximated by linguistic cues alone. This is done in precisely the same manner as you mentioned, as well as by judging vocabulary, grammar use, pronunciation, and pragmatics (appropriateness of responses). Computers are probably most advanced at this point in distinguishing pronunciation, but still trained phoneticians are used to diagnose and treat speech disorders, because software simply still isn't good enough. The variations you discussed are not well understood computationally or anatomically, so I don't believe there have been any good hypotheses other than those suggested by experience with children. SamuelRiv 04:02, 1 November 2007 (UTC)

Thanks SamuelRiv. I guess I wasn't as clear as I could have been. I was interested in specifically those differences that aren't linguistic in any way. That is, not vocabulary, grammar use, pronounciation or pragmatics, nor anything else for which it is require to assign meaning to the sounds. Rather, I wondered what kind of differences were recognisable in the pure sound-form of the voice, aucoustic qualities you might say.

In any case, I found a paper which is along the lines of the ideas I expected : [4] : though it still seems that there is woefully little work done on understanding speech outside of pathological/dysfunctional cases, which I guess is understandable, if not totally satisfactory. 81.153.3.36 12:09, 2 November 2007 (UTC) (Cross-posting to linguistics desk, just in case.)

[edit] Things stuck in eyesocket

Suppose something small and mildly irritating (like, say, a bit of cat fur) got stuck up under someone's eyelid and worked up into the eye socket. What would happen to it? Would the body destroy it or expel it somehow? How long would it take? Maelin (Talk | Contribs) 13:16, 31 October 2007 (UTC)m n

In general, this idea falls apart when you expect something to work its way behind the eye. The eye, if I remember correctly, is pretty much sealed in the skull. There's no way to, for instance, lose a contact lens behind the eye. If you somehow DID get something behind the eye, it would have been through a wound, and the effects of that wound would be worse than the object itself, I should think. --Mdwyer 14:39, 31 October 2007 (UTC)

I guess it's possible something could embed itself up there and work its way in somewhat. I would expect a cat hair to be absorbed over a long period of time because it's protein, but anything inorganic...I shudder to think. And I suppose that the body would try to do to such a thing what it does to all such things, like splinters. The eye is different though; inflammation alone can be a serious matter. See sympathetic ophthalmia here and here. I doubt the body would have time to deal with an embedded cat hair before the eye reacted unfavorably to it. You can tell by my wishy-washy reply that I'm no expert. --Milkbreath 15:43, 31 October 2007 (UTC)

The function of the eyelashes would prevent a situation like this from occuring. Their job is to keep foreign objects out of the eye (i.e. dust, dirt, debris, cat hair). They work in conjunction with your tears to do it. Even though the primary function of the tears are to lubricate the eye, they also function as a sort of safety mechinism, when an object gets into the eye (be it dirt, dust, or cat hair) the eye gets irritated and tears up. The offender then gets caught up in the tears and then is eaither flushed out or it gets near the eyelid and caught by the eyelashes and taken out of the eye. Lastly, a thin, but strong, membrane, called the conjunctiva, lines the inside of your eyelids and curls back on itself to cover the white part of the eye. This prevents any obects from going behind the eye. Hope this helps! Josborne2382 16:18, 31 October 2007 (UTC)

I've gotten specks of dust stuck between my eyelid and my eye. That's not quite behind the eye, but I still wonder how it always ends up getting out, and how I could get it out faster. — Daniel 03:26, 1 November 2007 (UTC)

I wear contact lenses around the clock, even while I sleep. There have been a few times where I've been woken by an irritated eye and found that one of the lenses has somehow moved to the top of the eyeball - i.e. not visible in the mirror. The process mentioned by Josborne kicks in and after a minute or two of teary blinking and rubbing the top of the eyelid, the lens is moved far enough forward for me to see it and gently remove it with my fingers. Oddly enough, in every case the contact lens has folded over on itself. I don't know if the lenses only float if they fold, or if they fold when they float high enough to encounter the fold of the conjunctiva. 152.16.59.190 04:32, 3 November 2007 (UTC)

I often have contacts "go for their morning swim" when I first put them in. They float back to places where I can't get at them, then work themselves back to the front after they finish doing their laps (a few minutes). StuRat 16:34, 3 November 2007 (UTC)

[edit] Hair loss

I asked my doctor about this but he didn't know exactly. I want to know if anybody has a link or two about uninterested reseaches on hair loss and effectiveness (if any) of treatments. I have quit given up hope on what constitutes medical advice so I'll just post fingers crossed and see if it gets deleted.193.188.46.254 14:03, 31 October 2007 (UTC)

The baldness article has a huge list of the various possible prevention/reversal treatments: Baldness#Preventing_and_reversing_hair_loss -- MacAddct1984 14:10, 31 October 2007 (UTC)

[edit] Freezing eye

Some time ago I read on how difficult it is for the eyes to freeze, but I forgot the reasons, could anybody patch me up on this? Also what would hypothetically hppend if you poured liquid nitrogen on somebodies eye? —Preceding unsigned comment added by 193.188.46.254 (talk) 14:16, 31 October 2007 (UTC)

I'd guess it is because they're salty, and salt depresses the freezing point. Still, LN is going to make them freeze anyway. Don't do it. :) --Mdwyer 14:34, 31 October 2007 (UTC)

It also helps that the human eye is embedded in a nice warm human being, equipped with all kinds of tools to maintain the body at a fixed 37°C. Heat is readily conducted from the back and sides of the eye socket (which, being right next to the brain, are well-supplied with nice, warm, constant-temperature blood) to the rest of the eye. Still, it would be possible to freeze the surface of the eye if you made enough of an effort—like by direct contact with a cryogenic liquid, for example. Tests in rabbit eyes gave the result:

Liquid nitrogen poured onto the eyes for one or two seconds with the lids held apart, produced no discernable injury. When the exposure was extended to five seconds, slight lesions of the corneal were observed. By the next day, all eyes were entirely normal.

I would expect longer exposure to do progressively more damage. Assumptions about the behaviour of human eyes based on the rabbit model should of course be taken with a grain of salt. TenOfAllTrades(talk) 18:43, 31 October 2007 (UTC)

Does it strike anyone else as odd that it is someone's job to pour chemicals into the eyes of rabbits? Man It's So Loud In Here 19:35, 31 October 2007 (UTC)

Rabbits are commonly used in animal testing. -- JSBillings 20:04, 31 October 2007 (UTC)

Not at all, how else would we determine the safety and efficacy of drugs formulated as eye drops? Rockpocket 20:21, 31 October 2007 (UTC)

How many brands of eye drops have liquid nitrogen in them? I'm no PETA pusher, but that's just insanely and purposelessly cruel to the rabbits. What's the next experiment: tossing bunnies into a wood chipper? Maybe we'll develop a better bandaid from it. Matt Deres 13:21, 1 November 2007 (UTC)

I agree. If scientists do things like pouring liquid nitrogen into the eyes of rabbits, which has little scientific benefit, the resulting backlash of public opinion could result in laws preventing important animal research, like testing eye-drops. Animal testing should only be used when absolutely necessary to protect humans. StuRat 16:29, 3 November 2007 (UTC)

[edit] Why do birds fly away from people?

I think this question is appropriate for the Science desk, since it seems to concern evolutionary biology. The question occurred to me this morning as I walked through a group of pigeons, which scattered as I approached them. This seems to be normal behaviour among our feathered friends, but when I stopped to ask myself why, I couldn't come up with an answer. In other words, why are birds scared of people? Of course, the answer that comes to mind first is that they are afraid of getting shot. Now, the chances of a pigeon being shot in a city street are pretty remote, although I guess the pigeon doesn't know that. So, is there some kind of evolutionary impulse at work here under which birds instinctively (and wrongly, in the case of city-dwelling birds) believe that man should be avoided? And if so, why hasn't this impulse atrophied among city-dwelling birds? --Richardrj ^talk ^email 14:25, 31 October 2007 (UTC)

Well, not just birds run away from humans. I can't think of any animal, unless it's a pet or trained, that wouldn't run away from a human. Humans are fairly big mammals, and if you saw something 10x the size of you, it's more than likely to benefit you to run away from it. Why hasn't the behavior atrophied? Probably because there is no selective pressure to fade out the trait. If running away from humans suddenly had a negative impact, such as they all started getting hit by cars when they try and fly away, then it's more than likely to weed out the trait. In the meantime, the pigeons have nothing to lose by flying away from approaching humans. -- MacAddct1984 14:39, 31 October 2007 (UTC)

Running/Flying away (Fight-or-flight response) is a pretty common behavior amongst animals. Not flying away from people is the unusual thing, probably bred into generations of city birds by the selective pressure of increased chance of food and less energy expense, as well as a lack of predators. Read about the Dodo to see what happens to a bird with few predators. -- JSBillings 14:40, 31 October 2007 (UTC)

(After edit conflict) A general instinctive fear of being killed and eaten by a creature much larger than themselves? The street pigeons seem to mostly tolerate humans, seeing them as something to simply move out of the way of - as they understand from experience that the majority of the large bipeds of the concrete forest pay them little attention and mean them no particular harm. They only seem to become agitated and take flight (around here, at least) if a human is getting too close, actively following them around, trying to trap them up against a wall, or running/walking towards them at speed - all of which the bird may (rightly?) interpret as hostile acts. --Kurt Shaped Box 14:43, 31 October 2007 (UTC)

Great answers. Thanks all. --Richardrj ^talk ^email 14:53, 31 October 2007 (UTC)

(another edit conflict) I think the 'rule' is probably more general than "man should be avoided" - something more along the lines of "if it's bigger than you and coming towards you, it should be avoided". Birds that tended to fly away when approached by something bigger than them would have an evolutionary advantage over those who hung around because that something may be a predator. Even if it's not a predator, it's extremely unlikely that it would be something that would provide the bird with some advantage over its fraidy-cat brethren who didn't stick around long enough to find out, so the wait-and-see trait would be disadvantageous and would die out. The impulse is still there because it's still advantageous, even amongst city-dwelling birds, to get out of the way of bigger things (imagine how odd would be if birds all wandered around on crowded streets, or didn't bat an eyelid if they were standing in the road and a car approached).

In fact, not all birds take flight as soon as they're approached by a human. Before it was banned, holding a handful of seed in Trafalgar Square was guaranteed to result in you being mobbed by pigeons. — Matt Eason ^{(Talk • Contribs)} 14:58, 31 October 2007 (UTC)

Yes, they're afraid because instinct tells them anything that gets close to them is probably trying to eat them! Although they are used to humans, they are still preyed upon by cats etc. Feral Pigeons are sufficiently tame to approach a human if they have food and some birds can be tamed so that they are not afraid of humans, my two pet budgies will run up to me and climb onto my hand if they are on the floor and I hold my hand out. It's just a case of convincing the bird that you are not going to harm it which takes time and perseverence. At the end of the day, one of the most basic instincts of all animals is to survive which means avoiding anything that is likely to be dangerous.GaryReggae 15:01, 31 October 2007 (UTC)

Actually, some birds tend to be fond of humans. It was (and sometimes still is) for a human to be feeding food to gulls, pigeons, sparrows, ducks, geese, etc. Some other birds, especially flightless ones, are not afriad of humans. That's what killed the dodo so quickly. One time, for example, we were having a picnic. A small ~3 in. tall bird (not sure what it's called) came towards the food, and actually landed on the picnic table. If we tried to swat it away, it would fly away, hover in the air, and come back. It often landed about a foot away from us. Another time, we were just minding our own buisiness, and walking near the shoreline at a lake, when a few dozen ducks and geese who were near the shoreline seemed to follow us. As we walked by them, they continued to follow us. The moral of the story is, feeding of birds, even in the past, has caused some of them to follow humans and trust any food given by them. Now there are some laws restricting feeding of birds, but apparently the birds don't know that. Hope this helps. Thanks. ~A H 1^(TCU) 23:49, 1 November 2007 (UTC)

[edit] If human bodies had thick fur like other mammals, do you think we would still wear clothes?

She didn't. Rockpocket 20:25, 31 October 2007 (UTC)

Do you? 64.236.121.129 19:16, 31 October 2007 (UTC)

Hmm, that's a fun question. It depends where our sense of modesty comes from. I would imagine without the invention of clothing and the ability to cover up, there would be no way for embarrassment of genitals to come about. However, clothing also provides an additional sense of style and individuality. So maybe, just being human, we'd wear some sort of clothing anyway -- MacAddct1984 19:47, 31 October 2007 (UTC)

Individuality could be expressed by styling and coloring the fur, but I think clothing would still have been invented. Much of it provides a lot of utility beyond keeping warm. Lab workers, for example, would probably still wear some variation on a lab coat. Police officers would still wear Kevlar vests. I'm no expert, but it seems like if our current attitudes towards clothing evolved from the need to cover up in cold weather it wouldn't be surprising if other uses for clothed eventually evolved into similar attitudes. 69.95.50.15 20:18, 31 October 2007 (UTC)

Also where would you put your wallet if your a man? Certainly i'd still wear clothes, gotta have a place for my phone, keys, wallet and iPod...You can see why mugging is so popular! The above stuff is right too, clothes are cultural-identity too, they are also a sub-culture thing. Goths, punk rockers, skaters, sports-addicts, 'chavs', horse & hound types etc. A lot of clothes (and styles) seem to have started their life as work-based clothing and/or developed to become fashion/general wear. Jeans were work-clothes (still are), Cargo pants, three-piece suit (though Adam Hart Davis suggests it was an attempt by the British to reduce the love of French clothing in the Stuart period), sports-wear is obviously often derived from sport-use clothing. Obviously work-wise these things are not just to cover modesty but as a form of protection/security/uniformity too ny156uk 23:38, 31 October 2007 (UTC)

Umm, that's what bags are for. Malamockq 23:04, 4 November 2007 (UTC)

It's a man's bag! Someguy1221 00:01, 5 November 2007 (UTC)

[edit] How much sugar does the average kid/adult consume on Halloween?

^topic 64.236.121.129 19:23, 31 October 2007 (UTC)

Can you have an average kid or adult? ΦΙΛ Κ 21:09, 31 October 2007 (UTC)

Well you would expect that in any 'holiday' season people will allow themselves more treats, so possibly some like say three times as much as the 'average' sugar intake on any other day. This article (http://www.sys-con.com/read/451581.htm) is basically utter garbage but it does mention halloween and sugar intake. ny156uk 23:33, 31 October 2007 (UTC)

Ugh, I've heard stories of kids eating all their candy in one day, and there's often several hundred pieces of candy! No wonder people get sick and diabetes. Besides, if you're counting average as in world average, then the average kid doesn't go out for Halloween, either because the local culture doesn't celebrate it, and/or because the locals are too poor to afford that much candy. Besides, if you ate all your candy in one day, chances are a few of them may have been tampered with (I remember getting candy with the package opened). Some people argue that eating all your candy in one day has the same effect as eating it over a longer period. This is a complete falsehood. It might be a bit close to the truth if you're not going to have a single piece of candy or other treat for the next 6 months. Besides, eating all your candy in one day can cause blood sugar (and fat, and plastic, and colouring, etc) levels to suddenly spike up. It's kind of like drinking a gallon of alchohol in one day instead of the same amount over a 6-month peroid. Hope this helps. Thanks. ~A H 1^(TCU) 23:58, 1 November 2007 (UTC)

[edit] Cyanide and suicide

Is suicide via ingestion of cyanide, as seen in James Bond movies, fact or fiction? Babalonia 3. —Preceding unsigned comment added by 66.74.109.242 (talk) 20:41, 31 October 2007 (UTC)

As can readily be found in our article on cyanide, it can quite easily be used as a poison. Adolf Hitler, among others, used it as such. — Lomn 20:57, 31 October 2007 (UTC)

When you say "as seen in James Bond movies" do you mean ingestion of cyanide causing death in seconds? Sifaka ^talk 22:52, 31 October 2007 (UTC)

I thought Hitler died from shooting himself (though his wife and dog were killed by cyanide pills). — Daniel 03:18, 1 November 2007 (UTC)

I think you're right. I'll hunt for a reference and fix the article. — Lomn 14:27, 1 November 2007 (UTC)

The references in Adolf Hitler suggest that he both bit a cyanide capsule and shot himself, then had his body incinerated, just to be sure. — Lomn 14:30, 1 November 2007 (UTC)

Which do you think killed him? I don't care how fast cyanide can kill. A bullet to the brain would be faster. By the way, does bit a cyanide capsule mean he swallowed a pill, popped some kind of tiny balloon with his teeth, or what? — Daniel 01:54, 2 November 2007 (UTC)

Tiny balloon. Fribbler 23:26, 6 November 2007 (UTC)

[edit] Exercising, Muscle Burn and Calories

Upon reading over several articles (such as muscle and exercising ), I’ve got a few questions relating to “muscle burn” after a rigorous workout. Assume that one runs a mile on a treadmill. Most treadmills indicate calories burned over the duration of the run. Further assume that, according to the treadmill, 200 calories are burned (let’s pretend this number is accurate). If the runner has muscle burn from the rigorous run, does he/she actually burn more calories than the 200 indicated by the treadmill? I would assume so, as the body is ‘recovering’ from the workout, and thus will burn additional calories post-run.

Thoughts? Rangermike 21:25, 31 October 2007 (UTC)

See Lactic acid and Delayed onset muscle soreness, if you are referring to the fatigue and soreness one feels in one's muscles during and after workouts.

This is out of my field, but the body is burning calories with everything you do, say, or feel, but nothing burns as quickly from homeostasis as physical motion. For a physicist's example, say you were sick, and you had a fever of one degree celsius. At a weight of about 100kg, you would burn 10^5 calories = 100 kcal (kilocalories or kcal are the actual unit of measure when people refer to "calories". One calorie properly refers to the heat necessary to raise the temperature of 1 gram of water by 1 degree celsius). Keep in mind, this fever builds up over several hours, whereas you can burn that much in a 30 minute workout. SamuelRiv 03:28, 1 November 2007 (UTC)

[edit] Gravitational pull of the moon

Hi,
I've heard that there is no instrument on the earth which can measure the gravitational pull of the moon (apart from the obvious affects of the tides). Is this true? --124.181.69.55 21:35, 31 October 2007 (UTC)

Let's see here.... The Earth will pull on a 1 kg mass with a force of 9.8 newtons. Using an Earth-Moon distance of 380 000 km, the Moon overhead would tug on the same mass with a force of about 34 micronewtons. So the apparent weight of an object due to the moon's motion over the course of a full lunar orbit will appear to vary cyclically over about 70 parts per million. That's not a huge amount, but it's certainly measurable. Particularly if one monitored a very stable, very precise balance over the course of several lunar orbits, I would expect the effect of the Moon's pull to stand out as a periodic oscillation. A very quick Google search for microgram balances finds this one, which will set you back about $7000, and which will measure masses up to 5 grams with a resolution of 2 micrograms (about 0.4 parts per million). Can someone check my numbers? TenOfAllTrades(talk) 22:05, 31 October 2007 (UTC)

I get 7 ppm from your numbers (2 * 34e-6 / 9.8) — Lomn 22:25, 31 October 2007 (UTC)

In theory, there's no reason you can't. In practice, it may be the case that tolerances don't allow us to (I'm not sure). Just for reference, though, here's what you're dealing with. Gravitation is a function of mass over distance squared. For the Earth, we'll say that it's M/R², where M is the mass of the Earth and R is the radius of the Earth, and we'll normalize that resulting number to 1. The Moon, on the other hand, masses roughly 1/80 Earth, and never gets closer (to the surface) than about 56R at perigee. Substituting, we expect that the Moon causes a discrepancy over a no-Moon Earth of 1/(80*56*56) -- that is, 4*10^-6 or 0.0004%. Now, in practice, that discrepancy can be roughly doubled -- the difference between the Moon directly overhead and directly underfoot (noting that the move from 56 to 58 Earth radii is pretty minor at this point). So in total, to detect the influence of the Moon's gravity on Earth-surface objects, you need accuracy to six digits, or one one-hundred-thousandth of the object. (ec) I notice that I'm an order of magnitude off Ten's answer. Time to double-check. — Lomn 22:13, 31 October 2007 (UTC)

I will note, however, that you're monitoring a periodic variation of [whatever the correct magnitude, 7 or 70 ppm] over a day, not a lunar orbit (month). Monitoring over the course of a month could be used to confirm the roughly 25% variation in the daily cycle resulting from the eccentricity of the Moon's orbit. — Lomn 22:18, 31 October 2007 (UTC)

Oops, right. The Earth rotates once a day, doesn't it? Dang. Double oops; you're also right about the 7 ppm (not 70). I'm going to have to turn in my physics license. TenOfAllTrades(talk) 23:02, 31 October 2007 (UTC)

LIGO has to compensate for lunar tides, so there is an example of an active experimental instrument that is sensitive to the moon's gravity. Dragons flight 23:43, 31 October 2007 (UTC)

They did it on an episode of mythbusters. They used an extremely powerful accelerometer to measure if the anti-gravidy contraptions had any effect whatsoever (they didn't). They breifly mentioned the accelerometer measuring the tidal forces from the moon and showed the graph it made. — Daniel 02:01, 1 November 2007 (UTC)

You may be confusing an important law in Special Relativity, which states that a person in a closed space can never tell whether he is being accelerated due to external gravity or some other outside force (such as a rocket). See the article for details. You may also be thinking of the Cavendish experiment, in which the gravitational force of the moon, the planets, and the Earth were all simultaneously measured by measuring the gravitational constant G, which combined with Newtonian orbit theory gives everything you could possibly want about gravitational forces in the solar system. SamuelRiv 03:27, 1 November 2007 (UTC)

The "apart from the tides" part of the question is pretty telling though. If a simple yardstick stuck into the sand at the low tide mark can detect the presence of the moons gravity, it's unlikely that there would be nothing else that could do the job. SteveBaker 01:15, 2 November 2007 (UTC)

The tides are a tiny deformation in the earth. A proportional deformation on an artificial device would be ridiculously small. Measuring the tides with an accelerometer is essentially the same as measuring height above sea level to the meter with one. Although what anon heard is wrong, it's not particularly misleading. — Daniel 01:51, 2 November 2007 (UTC)

I'm sorry, my point wasn't clear -- all you need to measure the gravitational pull of the moon is Newtonian gravitation (i.e. Kepler's Laws) and a measure for G (Cavendish). Then from Earth using parallax or radar we can calculate the Earth-Moon distance, and we know the period of the Moon's orbit around Earth and so we can calculate the mass of the Moon, and the Gravitational field of the Moon is then $\frac{-G*M}{r^2}$ , where M is the mass of the Moon and r is the Earth-Moon distance. SamuelRiv 02:15, 2 November 2007 (UTC)

[edit] oxidizers

are they flamible without fuel?

Various ether peroxides, like Acetone peroxide, Diethyl ether peroxide, and Tetrahydrofuran peroxide spontaneously explode when disturbed. Lab accidents involving such peroxides formed when a bottle of ether is exposed to light, oxygen, or catalytic metals and then subsequently ignored for a long time happen every once in a while. Sifaka ^talk 23:15, 31 October 2007 (UTC)

Thinking more about this, I bet some oxidizing agents with more complex chemical structures could react with themselves or other molecules of the oxidizer. There are probably also some nasty chemicals which have the potential to react under a variety of storage conditions without deliberately added fuel. Sifaka ^talk 23:28, 31 October 2007 (UTC)

[edit] oxidation

is mn203 a good pyrotechnic oxidizer? —Preceding unsigned comment added by 216.103.183.127 (talk) 21:59, 31 October 2007 (UTC)

I'm not getting any hits on google for manganese (III) oxide (also called manganese sesquioxide) being used as a pyrotechnic oxidizer. Safety precautions for the compound as listed in the sigma aldritch catalog (source) list it as an irritant to eyes, respiratory system and skin so I doubt people would appreciate it being scattered about by pyrotechnic displays where it could be inhaled. Among the applicable safety phrases it says don't add water to it. Of important note is that sigma didn't list it as an oxidizer, so I am leaning towards doubting its efficacy as an oxidizer at this point (I need to research around a little more). Many other manganese compounds appear to be fairly strong oxidizers including Manganese(III) acetate. Perhaps you meant to ask about one of them instead? Try looking at the manganese page. Sifaka ^talk 23:58, 31 October 2007 (UTC)

[edit] Tased across the spine

Can a person be paralyzed if the electrodes are opposite the spinal cord? I recently saw a video of someone getting tased in the back (the flying wires kind, not the little zapper kind) and it made me wonder --⁪ffroth 22:14, 31 October 2007 (UTC)

See Taser for details. The weapon uses a shaped electric current to disrupt nerve function, I suppose in a process similar to a localized seizure. Unless structural damage occurs to nerve fibres or bone, the current itself shouldn't produce permanent effects. The brain and spinal cord both have a certain degree of plasticity (ability to change - i.e. learning) that is believed to depend on the intensity and duration of electric currents. See Electroconvulsive Therapy for information on the effects of high-intensity electric currents on the brain. Permanent effects to the spinal cord could possibly be similar, but would only affect memories stored in the spine, namely "muscle memory". —Preceding unsigned comment added by SamuelRiv (talk • contribs) 03:38, 1 November 2007 (UTC)

My answer is "Sure, why not?" We tend to think of a relatively robust person getting tased, but suppose a frail child gets in the way? The darts can penetrate up to an inch, and from what I saw poking around the internet, you get millisecond-range currents of up 8.5 amps. That's a lot of current, however short the pulse. If the darts get deflected so that they land right next to each other on either side of the spinal cord, I wouldn't be surprised if it caused electrical burns in the tissue in between. It was hard to get solid information on electrically caused tissue damage by googling, and I don't know much about the specific direct effects of the taser waveform on soft tissue. There is a lot of propaganda out there spewed by parties with an interest in tasers, for marketing, for furthering the use of non-lethal force by police, and for opposing tasering as an invitation to police excesses. The truth has been effectively obscured on the internet, it seems. --Milkbreath 10:34, 1 November 2007 (UTC)

Well, when we got our Taser's late last year, we all had to "take a shot" to carry them, I have video's of it all. AFAIK every charge was administered via clipping one probe to the right rear shoulder, and one probe on the left pants pocket cuff, then having 2 people hold onto the victi... er administeree's arms. I'd consider that across the spine, no ill effects from any of us(though thats not to say it isn't possible, I believe elderly people or pregnant woman is what our SOP say to try to avoid tasing), minus the videos floating around of us yelling 'oh fuuuuuuuu', and yes I am not ashamed to admit I screamed like a baby and being in that large of a muscle mass it really takes a lot out of you. Yes, I had what appeared to be tissue burns on the spots where the probes were, they went away after about 2 days, and I can say there was no pain there, even the second the charge was up, I felt shaky but nothing else. Even out support staff (dispatch, admin aide, records clerk, evidence tech) all volunteered to take a shot, and yes, the women did seem quieter than the guys. Dureo 11:00, 1 November 2007 (UTC)

Oh and remember, the probes can penetrate deeper in winter, there are specifically longer winter probes for winter clothing, and yes unless they are torn out as they fall we have EMS handle removing them. Dureo 11:04, 1 November 2007 (UTC)

[edit] secret service mobiles

Just curious about how this locking down on mobile signal works and how do the mobiles that are manufactured against it work.88.203.105.48 22:42, 31 October 2007 (UTC)

When a police service says they're locking down the mobile phone system (usually because of a bomb threat), they generally mean that they're ordering the mobile phone companies to stop routing phone calls to mobiles in the relevant area. It stops people using a mobile phone to trigger a bomb. Aside from that, I'm not really certain that that's what you're asking. Can you be more clear (for example, can you post a link to a website or news article that spurred you to asked the above question)? --Psud 10:18, 1 November 2007 (UTC)

It's all just a matter of software. Every phone has it's own unique number - the cell towers know the numbers of the phones in their area. In case of an emergency, the computer in the cell towers can decide what they want to do with calls. If it's an emergency, it could (for example) stop routing calls from any phone that's not listed as belonging to an emergency worker. This stuff is very easy to do if you have the inclination. SteveBaker 01:08, 2 November 2007 (UTC)

By locking down I meant pin point the location of the user of the mobile 193.188.46.254 09:18, 2 November 2007 (UTC)

They used to locate mobile phones by asking the phone company which phone towers it was communicating with, mobile phones keep in contact with several towers to allow instant handover as you move between cells. It's a simple matter of looking for the phone/person in the area where the various towers' signals overlap. That's the simple version anyway (and I don't know enough to give you the complicated one). The new way they look for phones is by asking the phone for its GPS position. Only works with phones with GPS. The old method works with any phone, I think. Perhaps it could be defeated by hacking the phone so it talks to the "wrong" mobile phone towers. It'd probably be trivial to hack a GPS equipped phone to report a wrong location. --203.22.236.14 09:58, 2 November 2007 (UTC)

If you read through the GSM specs you might find some information. But basically the terminal (the handset) measures the signal strenght to decide which tower it should 'speak' to, this strenght can (is) quantifiable and thus the handset would be able to determnine the nearest tower. It might be that towers also has the capability to measure the signal strenght from a particular terminal...and then you would be able to triangulate the position....I don't know all the details though :-) (aza----)

GSM phones can use Timing advance to determine distance from a known tower. Usually, the phone will hit only one of three antenna sectors around a tower. Many CDMA phones actually contact multiple towers at the same time, making triangulation much more likely. In addition, many CDMA phone have specialized GPS hardware. --Mdwyer 22:22, 5 November 2007 (UTC)

[edit] Rising Sea Levels and the Effect this Will Have on the Mediterranean Ocean

Given that the Med is regarded (more or less)as a tideless sea and that this is largely due to the influence of the Straits of Gibraltar which constrict the tidal bulge caused by the gravitational pull of the sun and/or the moon. At what point, if at all, or to what degree, in the earths future, will the Med see a real tidal effect once the seas have risen enough to overcome the resistance of the Straits of Gibraltar? Much of the Med coastline is at or very near sea level because there has never been any need to make allowances for tidal fluctuations. —Preceding unsigned comment added by 79.68.42.88 (talk) 23:08, 31 October 2007 (UTC)

Well much of all society is near the sea/lakes because historically we settled near places with ready access to water. The med problem is interesting. I expect it would require an extremely large increased. As the article (Strait of Gibraltar) notes water depth ranges from 300m to 900m, the opening is some 8 miles wide - having said this the end of the article has a bit on the 'need for a dam' so might be worth having a look at that link (http://www.agu.org/sci_soc/eosrjohnson.html) ny156uk 23:28, 31 October 2007 (UTC)

[edit] facial hair

Why do males have facial hair? Why don't females? —Preceding unsigned comment added by 68.231.151.161 (talk) 23:45, 31 October 2007 (UTC)

Vestigial trait. Doesn't serve any meaningful purpose unless you are white, it can sort of protect the face from UV radiation, but melanin (dark skin) does a much better job of that, and protects everywhere. So in other words, it's useless from a utilitarian point of view, but has cultural and social significance. Malamockq 01:24, 1 November 2007 (UTC)

Facial hair is a secondary sex characteristic resulting from the differential effects of sex hormones on the body. Rockpocket 07:50, 1 November 2007 (UTC)

Some women do have facial hair. -- JSBillings 10:25, 1 November 2007 (UTC)

In theory it helps to protect against the cold in high northern places like Scandanavia or Russia. As to why women dont, I dont know. But look at most antarctic scientists, they have big beard for the cold. If you have hair, when was the last time your head got cold? —Preceding unsigned comment added by 12.191.136.2 (talk) 15:08, 1 November 2007 (UTC)

I would conjecture that the standard explanation of gender differences, that of men going out to hunt and women staying at home with the family, can explain this. Men were more likely to find themselves in very cold situationsunexpectedly, where some extra insulation around the mouth would be welcome. There's a lot of blood in the lips and tongue, so it's an important area to keep warm. The women were relatively sheltered at home, so they could do without the facial hair, which gave them the advantage of being able to communicate with a greater degree of freedom, which would have been an important factor in the development of the children. I'm not sure how much I believe in this explanation myself, since people from warmer climates seem to have just as much facial hair as people in colder climates. I don't think that Inuit have a big culture of facial hair, and muslim countries certainly do. Maybe there's another hunting related advantage to beards.risk 04:15, 3 November 2007 (UTC)

And, once any difference in a trait exists between the genders, it will serve to differentiate the sexes. Thus, women will be attracted to men with facial hair and men won't be attracted to women with it, thus perpetuating the trait. It also works as an age marker, since young boys lack facial hair. StuRat 16:15, 3 November 2007 (UTC)

[edit] Finite from Infinite

Today's science dictates that not only is a theoretical construct of infinite density, energy, and size possible; it's actually how the universe started. How does a finite universe come from something that is infinite? —Preceding unsigned comment added by Sappysap (talk • contribs) 23:55, 31 October 2007 (UTC)

Firstly, there is no accepted theory suggesting the Universe is finite. While the observable universe is quite finite, the actual universe is possibly infinite in extent and mass. Further, physics does not posit that the universe began in a state of infinte density. It actually doesn't posit anything accepted about where it came from, as the Big bang theory only deals with what happened after (very soon after, though) the universe started existing. Someguy1221 00:27, 1 November 2007 (UTC)

Thirdly one way to look at it is fintite mass divided by zero size gives infinite denisity. Graeme Bartlett 00:30, 1 November 2007 (UTC)

I'm a huge fan of all of you guys who answer these questions...Someguy1221, Rockpocket, SteveBaker, Dragon's Flight and the whole crew. Please have infinite patience with me while I ask the following: How can the universe have infinite mass without infinite density? How can it have infinite extent and continue to expand? Sappysap 01:07, 1 November 2007 (UTC)

As for the first, I'm still trying to get my head around it, but for the second, imagine a piece of elastic, infinitely long, with small knots tied at regular intervals. Now imagine the elastic being stretched - you'll see the knots moving apart, even though you can't see the "ends" moving apart. Confusing Manifestation 02:00, 1 November 2007 (UTC)

To answer how the universe can have infinite mass without infinite density, all you have to do is think of numbers. There are infinitely many integers, as I'm sure you're well aware. There are also infinitely many numbers inbetween every two integers. And so, you manage to have a system of infinitely many numbers containing an infinite number of integers yet not every number is an integer. Actually, as you might suspect from there being infinitely many numbers between two integers, and only finitely many integers between any two numbers, each integer is like a tiny island in the sea of infinity. So, in conclusion, your infinitely many integers occupy an infinitely small portion of the number line. So I think you can see from this how you can have, in an infinitely large universe, infinitely many masses without filling up every possible space with a particle. As for having infinite extent, I haven't quite figured or accepted that one yet, except to say that lots of astronomers believe this (it is in part just a conclusion from the evidence that the Universe has no center or edge). Someguy1221 02:33, 1 November 2007 (UTC)

The universe has infinite mass if and only if it has infinite volume. Obviously everything around us has finite density, but if you allow yourself to collect more and more of it without limit, then ultimately you arrive at an infinite amount occupying an infinite volume. It is unknown whether the universe is truly infinite in extent, but it appears likely that it must be very much larger than the observable universe we can see. Dragons flight 03:26, 1 November 2007 (UTC)

None of the above physical quantities are or ever were truly infinite. The widespread modern cosmologies (that is, those based on Einstein’s general relativity, which came out about 90 years ago) all involve a universe that is finite in size and energy (or mass). And I’m talking about the entire universe, not just the visible universe. It isn’t really accurate to say that the density of the universe was infinite at the exact moment of the big bang, either. Singularities in a physical theory generally indicate a point at which the physical model breaks down, not that there really is an infinite physical quantity at that point. In this case, physics within the Planck epoch are poorly understood, but it appears that it is meaningless to talk about distances less than one Planck length, which is a finite distance, or time intervals shorter than the Planck time, which is also finite. So it isn’t meaningful to talk about energy densities greater than the (finite) total energy of the universe divided by the volume of a sphere whose diameter is a Planck length, or meaningful to talk about the exact instant of the big bang. MrRedact 02:46, 1 November 2007 (UTC)

I'm not sure what the initial question refers to, specifically. There are indeed important resolutions of infinite results in Quantum Field Theory, which I might be able to expand upon if a detailed question is posted, but all "physical" results must be finite by definition. Unresolved singularities (infinite results) signify a failure of a theory, not a physical reality. Cosmology works a little differently, but even then most cosmologies I know of do not accept any premise of infinity except perhaps in the context of a ground state (see vacuum). SamuelRiv 03:45, 1 November 2007 (UTC)

You are confused. General relativity permits solutions that are either infinite or finite in extent, and so is essentially agnostic on the issue. (See for example: Friedmann-Lemaître-Robertson-Walker metric, which permits different homogeneous and isotropic solutions discriminated primarily by whether the universe is finite or not.) For the universe to be finite, it must have a global curvature such that a person traveling in what appears to him to be a straight line will eventually come back to places he has been before. Such a curvature is possible, but not required, in GR. Your description of the Planck quantities is also problematic. It is not that there couldn't theoretically be smaller lengths, times, etc., but rather that describing events at those scales intrinsically requires both an unified understanding of gravity and quantum mechanics. In other words it requires an as yet ill-defined theory of quantum gravity. So, it is meaningless primarily in the sense that science as it now exists is not able to provide it meaning. Future theories may yet shine a light on events in and before the Planck epoch. Dragons flight 04:09, 1 November 2007 (UTC)

Ouch. I should have researched this one a little better before responding. I’m obviously not an expert in cosmology. Einstein himself assumed closed boundary conditions on his field equations, which implies a finite universe, but what slipped my mind for some reason was that not everyone assumes those boundary conditions.

My description of the Planck quantities very closely echoes a sentence in the Planck epoch article: "When quantum mechanics is combined with gravity, it turns out that it is meaningless to speak of time intervals shorter than the Planck time or distances shorter than one Planck length." That sentence, at least, is consistent with my understanding that "space" and "time" are ill-defined concepts at shorter times and distances. Of course, it’s all highly speculative, in the absence of a good theory of quantum gravity. MrRedact 10:36, 1 November 2007 (UTC)

See also ebooksgratis.com: no banners, no cookies, totally FREE.