Wikipedia:Reference desk/Archives/Science/2008 April 25

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April 25

What's inside a snooker ball?

Are they solid plastic all the way through, or is there something else in the middle? --Kurt Shaped Box (talk) 00:42, 25 April 2008 (UTC)

See Billiard ball. DMacks (talk) 02:21, 25 April 2008 (UTC)

Billiard balls today are solid polymer, often a phenolic resin, polyester, or acrylic. This site has a cutaway picture. TenOfAllTrades(talk) 02:27, 25 April 2008 (UTC)

According to that site, the momentary "instantaneous" impulse, or collision, of stick against ball, has a "resulting friction temperature between ball and cloth can easily reach 250°c". What does this mean? I am not familiar with the term "friction temperature"; it seems like any heat would be absorbed by the relatively large heat-sink that is the mass of the billiard ball. Also, I was always taught that a billiard-ball is about the best example for a perfectly elastic collision, with virtually no energy lost to the impact deformation due to material stiffness. Comments? Is "friction temperature" just marketing-ese to sell more billiard balls? Nimur (talk) 05:42, 25 April 2008 (UTC)

When the ball skids across the felt the temperature on the surface of the ball would be 250C. The ball is a poor conductor of heat so any heat generated will not be transmitted will throughout the ball, thus the temperature at a local point can get quite hot. When the ball is skidding it is not elastic, when they are rolling and collide then it is close to an elastic collion.--Shniken1 (talk) 06:58, 25 April 2008 (UTC)

So the stripe goes all the way through? Interesting. I'd always thought that it was just a surface feature... --Kurt Shaped Box (talk) 22:54, 25 April 2008 (UTC)

Looks like it. Just like Blackpool rock —Preceding unsigned comment added by 79.76.217.249 (talk) 03:27, 26 April 2008 (UTC)

So, Snooker ball now redirects somewhere useful. Who was it that said that the Reference Desk did little to improve the encyclopedia? ;) --Kurt Shaped Box (talk) 19:50, 26 April 2008 (UTC)

Derivore

What is a derivore? 99.226.26.154 (talk) 00:43, 25 April 2008 (UTC)

Are you sure you don't mean detrivore? —Keenan Pepper 02:00, 25 April 2008 (UTC)

Or maybe an hors d'œuvre? Nimur (talk) 05:44, 25 April 2008 (UTC)

IDing Tanzanian termite-raiding ant

I know trying to ID insects from s.o.'s description can be an exercise in futility, but I hope I can provide enough details to narrow it down to the family at least.

I have come across colonies of similar, perhaps the same, large black ant in Tanzania, both near the coast on sandy riverbanks in forest reserves in Dar es Salaam, and upcountry in acacia scrub in the Rift Valley, within sight of Ngorongoro and the Serengeti. They're ~~1cm long, not particularly numerous (one colony a hundred or so, another maybe a thousand), and they emit a noise that sounds like rain when disturbed. Although I've never been stung, I've seen the effect on others, and it's clearly painful, though even a 4-yr old will stop crying after 5-10 minutes, and there's no swelling (from a single sting, anyway). However, they have one of the more painful ant stings in the area. They're diurnal hunters, and hit harvester termites on their forays. (Prob'ly other things, but termites is what I've seen.) In Swahili they're known as sungu-sungu, though there's so much regional variation in species and names that that might not be much good for an ID. They're larger than the siafu.

Anyone have any ideas?

Thanks, kwami (talk) 01:29, 25 April 2008 (UTC)

Hi Kwami, Sungusungu gets this: (Tanzania) they are (Kiswahili) "biting ants" and "In Swahili, Sungusungu denotes a highly cooperative and aggressive type of ant; in the Sukuma language, it means poison." in an article on vigilante groups[1]. Hard to find anything on them in entomology, except vaguely that they are meat-eating and get this, "small ant"[2]. Only the Carpenter ant is termite specific and widespread but nothing about origins. (addn) PS have you seen this[3]?Fwiw, Julia Rossi (talk) 09:18, 26 April 2008 (UTC)

Thanks. Carpenter ants are formicins, which makes sense since they may nest in the walls of houses, but it doesn't fit their sting — but then, I've never been stung, so maybe I'm wrong on that. They are the right size.

When you say 'termite specific', do you mean in nesting, or raiding?

kwami (talk) 10:13, 26 April 2008 (UTC)

Had in mind raiding. Julia Rossi (talk) 12:22, 26 April 2008 (UTC)

More Quantum Theory

According to Zeno's paradox#Does Quantum Theory solve the paradox?, it states that Planck length and Planck time are the smallest mesurable units of their respective dimensions. It then implies that space may be discontinuous and not infintely divisible, having the Planck length as the smallest unit of traversable space. How could this be? Where could I find more information about this? Furthermore, why is it (Planck length) the smallest mesurable unit of space, the Planck time the smallest mesurable amount of time? Why can nothing smaller be meaured? Thanks, Zrs 12 (talk) 02:50, 25 April 2008 (UTC)

Planck units are expressed in terms of relations between fundamental constants; our theories which use such constants don't make any sense if you start talking about units smaller (or in some cases larger) than Planck units. When you're thinking about things that small you can't let yours intuitive concepts interfere—length, time, matter, etc. don't operate on those scales the same way they do on more macroscopic, human scales. The easiest way to make sense of Planck units is to start by understanding the importance and implications of a quantum of energy (quantum), and then think about what it would mean to establish that sort of thing for other measurements. It's pretty unintuitive when you first come across it but there are pretty unimpeachable experiments that support it. --68.125.224.4 (talk) 03:54, 25 April 2008 (UTC)

Why can nothing smaller be meaured?. What are you going to measure it with? If the smallest measuring rod that can be constructed is a planck length and the smallest clock tick is the planck time, then it is not possible to construct a measuring instrument that can measure anything smaller. SpinningSpark 09:22, 25 April 2008 (UTC)

It does not automatically follow that you can't measure something smaller than the smallest measuring stick you can construct. It's easy to measure beyond the resolution of your measuring device. You can introduce some random noise known to average to zero and then measure the signal plus the noise and average over a large sample. The great part is that the noise can be several times larger than the signal, as long as it averages to zero you still get a measurement at greater precision to your measuring stick.

I'm not qualified to comment on this in regards to the Plank length, though. I imagine there are other difficulties that go beyond simple resolution restrictions on a measuring stick. APL (talk) 13:25, 25 April 2008 (UTC)

You assume that there exists something smaller to measure. If no such thing exists, it is impossible. For instance, if the charge on an electron were the smallest possible charge (I know about quarks, but am going to ignore them for this discussion) then your charge meter can only go up and down by whole electrons at the very best resolution that can be constructed. This is not some deficiency in my skill at constructing the meter. It is because the meter itself must necessarily use electron charge in the parts from which it is constructed. If you then add noise, you can only add noise in +/- whole numbers of electrons. You might get an average that is not a whole number but that does not mean that there is a fractional number of electrons in the box. It just represents the statistical error due to a less than infinite sample. SpinningSpark 10:02, 26 April 2008 (UTC)

You might want to read Heisenberg uncertainty principle, Planck length#Physical significance, and Planck time#Physica significance. The last section brings up some possible evidence to challenge this theory, but information is sketchy; you might want to follow up with the references. --Prestidigitator (talk) 18:34, 25 April 2008 (UTC)

Type of spider in Spider fighting

Can anyone identify the spiders in the article? These spiders are orb-weavers, roughly .5 to 1 cm long. They live in trees, power lines and tall grasses. They are found here in the Philippines. I posted this question on WP:SPI on August 2007 but didn't get any replies.--Lenticel ^(talk) 05:58, 25 April 2008 (UTC)

Hi Lenticel, I get a type of Argiope and there's one here[4] close-up. Addn: Aka a type of garden orb weaver[5]. Julia Rossi (talk) 01:37, 26 April 2008 (UTC)

The spiders looks more like Araneus (dull colored) than Agriope (larger and strikingly colored). I read List of Araneus species and found out that there are many species of Araneus in the Philippines. Well at least we narrowed it down to the genus level. Thanks Julia!--Lenticel ^(talk) 07:11, 26 April 2008 (UTC)

Ah, found it confusing colorwise especially sinceboth g's have their less vibrant types -- the Araneus I found looked highly coloured and ball shaped. Do they also like to web around power lines? happy searching,  : ) Julia Rossi (talk) 07:46, 26 April 2008 (UTC)

PS You've got a few Argiopes in the Philippines too – those spiders get around! Julia Rossi (talk) 07:51, 26 April 2008 (UTC)

Yes they do spin webs in power lines. Kids prefer these spiders as fighters as they are "brave" enough to show themselves openly to predators. Yes we do have Argiopes here which we call gagambang ekis (X spider) due to their X like decorations--Lenticel ^(talk) 11:13, 26 April 2008 (UTC)

A tip from an arachnidologist: that the size of a web shows how powerful a spider is – poor spider, Julia Rossi (talk) 13:06, 26 April 2008 (UTC) PS Thanks for the link to decorations - didn't know we had that article. JR

Shells

Hi, What is actually the shape of each shell of an atom ? Is it a 3-D spherical shape, or an ellipse like that of the planets, or something else? Thanks. 116.68.70.51 (talk) 10:37, 25 April 2008 (UTC) A 15 year old.

See Atomic orbital. It differs between difference subshell types. s-orbitals are spherical, but the others aren't as simple. 83.253.253.166 (talk) 10:59, 25 April 2008 (UTC)

The shapes are usually modeled as Legendre polynomials in spherical coordinates, because these forms are solutions to the governing equation of an electron. The easiest solution is of course the sphere, or s orbital. However, the higher order shells are very complex and may exhibit weird geometries (e.g. quantum effects) - for example, the electron's distribution function may be finite on both sides of a node and zero in between. Nimur (talk) 14:32, 25 April 2008 (UTC)

Thank you! 116.68.71.144 (talk) 13:12, 26 April 2008 (UTC)A 15 year old

Eyes

Hi! This is the same 15 year old again.........What I want to ask is, when an eyelash falls in the eye, somewhere in the white portion, I might not even notice it, but if it falls on the pupil, I would get a prickly stinging sensation immediately, even if it touches only a small portion of my iris and doesn't interfere with vision. Why is it so? I thought that the conjunctiva covered the front of the eye evenly. How should I know precisely when something touches only a certain portion?? (The conjunctiva doesn't have nerves, does it??) 116.68.70.51 (talk) 10:45, 25 April 2008 (UTC) A 15 year old

My understanding as someone who hasn't studied the eye, but has worn contacts for a very long time, is that the eye itself has no sensory nerves and doesn't notice anything on it. Your eyelid, on the other hand, is very sensitive and notices immediately if there is anything disturbing the smoothness of the eye. An eyelash "in your eye" is only noticed as it gets "run over" by the lid. -SandyJax (talk) 15:03, 25 April 2008 (UTC)

However, if you see the eyelash fall, that may trigger the "I've got something in my eye" feeling, too. So, lashes which fall in your field of view are more likley to cause a reaction. StuRat (talk) 15:27, 25 April 2008 (UTC)

There are no nerves (motor or sensory) in the sclera (white of the eye) so nothing can be felt on it. The pupil doesn't have any nerves either, but (as StuRat mentioned) I believe when the eye visually notices something on the pupil, it triggers a response; namely, pain to help you know it's there and the eye starts to secrete tears. Regards, CycloneNimrod^Talk? 16:43, 25 April 2008 (UTC)

I have difficulty believing that there are no sensory nerves on the sclera or pupilcornea. If I hold my eyes open to let them dry out, they begin to sting, and that sensation is definitely on the surface of my eyes. If I take a tissue paper and poke it into different places on my eye, it tickles or even hurts. This also happens in the dark if I can't see what's happening. I'm skeptical that a visual cue will trigger a physical pain response localized on the eye surface. ~Amatulić (talk) 18:53, 25 April 2008 (UTC)

The pupil isn't part of the surface of the eye. Think of the surface of the eyeball as consisting of two parts: the white part, the sclera, and the clear part (which overlies the iris, lens, and pupil), called the cornea. The sclera has very little in the way of neuroreceptors, but the cornea is one of the most sensitive and densely innervated tissues in the body. Corneal abrasions are exquisitely painful. - Nunh-huh 20:07, 25 April 2008 (UTC)

The entire surface of the eye has sensory nerves that are used to trigger tear formation. I've done work on two studies involving sensory nerves on the eye. One found reduced sensation and reduced tears in patients who had LASIK. Another found that lack of sensory nerves on the surface of the eye correlated with early onset of glaucoma. -- kainaw™ 00:42, 26 April 2008 (UTC)

Cellphone signal

Someone told me today that numbers like 911, 112 and 999 (emergency numbers) can be called without any signal. I doubt very much that this is possible, but if it is, someone please explain how it can be? Thanks! Regards, CycloneNimrod^Talk? 16:54, 25 April 2008 (UTC)

Perhaps what was meant was that emergency numbers can be called without a service plan; since a cell phone is, at a very basic level, a radio transceiver, a signal is necessary to make it work. --LarryMac | Talk 17:07, 25 April 2008 (UTC)

Agreed, they had the terms mixed up. Or you do. Either way, cell phones can call emergency numbers without any service plan. In fact, many communities have charities for abused women that give away old cell phones for free. They give them to women who may be in danger from their ex-husbands and so forth, so that if the need arises they can call 911 without having to pay for a service plan. see this, this, and this. Dismas|^(talk) 17:17, 25 April 2008 (UTC)

From a user point of view it can seem as if they operate without any signal, and if you define 'signal' as the thing that your phone tells you it has (as is the way many lay people use it), then it does. Often when I don't have any 'signal' (I have no bars lit up) my phone says 'emergency only', meaning it can only be used to call 999 or 112. This is because there is no signal for my network, but other transmitters for other networks can be reached if necessary. 79.66.99.37 (talk) 17:33, 25 April 2008 (UTC)

QI tells us that on Christmas Day, lots of Americans call 911 to test their new phones because they have no network. -mattbuck (Talk) 14:53, 26 April 2008 (UTC)

That seems highly unlikely, due to the nature of the cell phone business in the US; i.e. phones and plans are tightly coupled and purchasing a phone without having it already set up with a carrier is not the norm. I'd like to know where QI sourced that factoid. --LarryMac | Talk 15:18, 28 April 2008 (UTC)

The phones probably were already associated with a carrier, but not activated and thus couldn't be immediately used. - Pureblade | ^Θ 17:58, 29 April 2008 (UTC)

NAV (Anatomy)

I've been cleaning up the NAV disamb page and I just want to check whether the following is correct:

In anatomy, NAV stands for nerve-artery-vein, when all these follow a common pathway.

Zain Ebrahim (talk) 17:05, 25 April 2008 (UTC)

True, a useful mnemonic for the order of vessels and nerves on the front of the upper thigh, for example. A fuller version is NAVEL - (lateral to medial) Femoral nerve, femoral artery, femoral vein, empty space with lymphatics. I tidied up the NAV (anatomy) page a bit. -- Flyguy649 ^talk 01:47, 26 April 2008 (UTC)

And yes in shortform, writing "Femoral n.a.v" would mean all three. -- Flyguy649 ^talk 14:38, 26 April 2008 (UTC)

What causes dark circles under the eyes?

What causes dark undereye circles? --70.167.58.6 (talk) 18:54, 25 April 2008 (UTC)

The eye circle article has an answer, although it isn't cited with reference. ~Amatulić (talk) 20:30, 25 April 2008 (UTC)

The two explanations in the article for dark circles resulting from lack of sleep or fatigue seem utter bollucks. How would lack of sleep "make the skin pale" to the extent that the underlying blood vessels become more visible, but nowhee elso on the body? What layer of the skin would "become pale?" I thought pallor is more often associated with a decrease in peripheral blood flow. The other explanation is that "when one lies down since gravity can cause fluid to collect in the lower eye lid" again unsatisfactory because when I have stayed up all night, by definition I have not been lying down, and this assuredly results in dark circles. Edison (talk) 01:27, 26 April 2008 (UTC)

I think you've misunderstood the second explanation (though it still seems dubious to me). The article seems to state that lying down allows the blood to circulate more freely and it's standing (or sitting) up that causes the blood to be trapped, thus agreeing with your experience. By extension, that should mean that lying down, even without sleeping, should be enough to prevent the formation of the circles, but that hasn't been my experience. Matt Deres (talk) 20:09, 30 April 2008 (UTC)

cockateils

moved from Village Pump -- Kesh (talk) 21:44, 25 April 2008 (UTC)

We have questions about weird things our bird does. what size are their hearts? our bird will look straight ahead at us and we can barly see his eyes...can he see us? also...he does this weird thing with his mouth. It looks like he's yawning, but he'll do this over and over again. & whats the best way to start petting him? He's used to us, but he doesnt like us touching him. Whats he doing? Thanks email removed —Preceding unsigned comment added by 209.33.106.106 (talk) 17:09, 25 April 2008 (UTC)

Guess you've seen our article Cockatiel - it's a start, especially about getting to know your little bird. Julia Rossi (talk) 12:26, 26 April 2008 (UTC)

Maybe by putting User:Kurt Shaped Box's name here, he will notice this question. Kurt is the resident bird/gull/budgie expert and may have useful insights. Nimur (talk) 14:36, 26 April 2008 (UTC)

This site [6] has lots of good information on bird behavior and training.--Eriastrum (talk) 16:12, 26 April 2008 (UTC)

Just saw this topic. WRT your Cockatiel's repeated 'yawning', it could be one of a few things - but it *may* mean that there's something wrong with him. It could be the case that he's actually gasping for breath, for instance. You should probably take him to an avian veterinarian and get him checked out, just to be on the safe side. Birds are *very* good at hiding illness - they often don't appear to look sick at all until they're almost at the point of keeling over, so you do need to keep a close eye out for any behaviour that appears to be out of the ordinary. Pet birds are also generally prone to respiratory problems, be they environmental in cause or due to an infection. --Kurt Shaped Box (talk) 23:14, 27 April 2008 (UTC)