Wikipedia:Reference desk/Archives/Science/2011 November 2

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November 2

Forces on an inclined plane

If I have a block sliding down the inclined side of a frictionless wedge, should I include both the weight of the block and the reaction force of the block against the wedge as forces exerted on the wedge? Thanks Luthinya (talk) 00:36, 2 November 2011 (UTC)

No. The weight of the block is exerted on the block, not on the wedge. Only the reaction force is exerted on the wedge. --140.180.14.123 (talk) 01:01, 2 November 2011 (UTC)

George Dantzig

What were the two unsolved statistics problems that George Dantzig famously solved as though they were mere homework? The references in his article don't appear to say. (This question was inspired by a recent thread on the Computing desk.) Comet Tuttle (talk) 01:18, 2 November 2011 (UTC)

Apparently that information is somewhat obscure, and probably not very interesting. Here is a pretty detailed account of what happened from Snopes. Looie496 (talk) 01:29, 2 November 2011 (UTC)

Yes, that is one of the references I mentioned, and, as I mentioned, it does not say. Thank you for opining that it's probably not very interesting, of course. Comet Tuttle (talk) 01:33, 2 November 2011 (UTC)

Okay. The two papers are:

• On the non-existence of tests of "Student's" hypothesis having power functions independent of σ. (first ref in our Dantzig article)

• On the fundamental lemma of Neyman and Pearson, by George Dantzig and Abraham Wald.

They can be found as the first two chapters of the book The Basic George B. Dantzig. Looie496 (talk) 02:00, 2 November 2011 (UTC)

wave

it is said that when wave propagates it propagate with momentum and energy ,here iam able to understand how energy is propagated but how momentum is propagated? — Preceding unsigned comment added by Bhaskarandpm (talk • contribs) 01:35, 2 November 2011 (UTC)

Momentum is a manifestation of kinetic energy in mass. Dualus (talk) 01:45, 2 November 2011 (UTC)

Photons have no mass; I have a different definition of momentum - the change in action per metre. Plasmic Physics (talk) 03:20, 2 November 2011 (UTC)

Photons have no rest mass, but they are never at rest, so they always have a relativistic mass. --Jayron32 03:21, 2 November 2011 (UTC)

I know that, I don't count relativistic mass as true mass. My definition still holds, doesn't it? Plasmic Physics (talk) 03:24, 2 November 2011 (UTC)

I don't know; if you are inventing your own definitions, you can decide if they are true or not without any help from me... --Jayron32 03:28, 2 November 2011 (UTC)

To clarify, pressure inside an isolated vessel of a gas can be defined as the force exerted per squared meter, or the energy charged per cubic meter that is, the amount of work that one cubic meter can perform. There are limitations to the definitions of pressure, for instantance, it is impossible to define pressure purely interms of time. Likewise, there are limitations on the definition of momentum. Plasmic Physics (talk) 03:59, 2 November 2011 (UTC)

Maybe I should change my definition to instantaneous action per metre, otherwise I would be defining impulse rather than momentum. Plasmic Physics (talk) 04:31, 2 November 2011 (UTC)

Is this new definition different from the rate of change in action with repect to distance? Plasmic Physics (talk) 04:36, 2 November 2011 (UTC)

alloy NF616, HCM12A, E911

I do not know where to get the information about properties of alloy NF616, HCM12A, E911,such as the melting point,specific heat,density,conductivity and so on. Thank you ! — Preceding unsigned comment added by Demonhunter20030901 (talk • contribs) 07:13, 2 November 2011 (UTC)

Try asking about NF616 etc on WP:RX. Dualus (talk) 10:20, 2 November 2011 (UTC)

Outer Covering of Animals

What is the outer covering of insects ?

See Insect#Exoskeleton. Sean.hoyland - talk 09:55, 2 November 2011 (UTC)

No fair asking us for the answer...that's chitin ! StuRat (talk) 01:07, 3 November 2011 (UTC)

Best response ever 217.158.236.14 (talk) 16:27, 3 November 2011 (UTC)

Neutrino

If we had a slab of lead a million miles thick what would be the probability of a neutrino reacting as it passed through? (Does someone have a better example of how penetrating a neutrino is? And yes, I know that much lead would collapse under its own gravity.) RJFJR (talk) 16:28, 2 November 2011 (UTC)

It isn't a fixed number. Neutrino interaction probability depends on the energy of the neutrino -- generally speaking the higher the energy, the higher the probability of interaction. Looie496 (talk) 16:34, 2 November 2011 (UTC)

If you are looking at how hard it is to detect neutrinos, you may want to read neutrino detector. An example in there is a very sophisticated detector that detected 19 out of a billion trillion trillion trillion trillion neutrinos. -- kainaw™ 16:35, 2 November 2011 (UTC)

that page will give you a explanation of how to do a Back-of-the-envelope calculation for that. The formula is $L={\frac {m_{p}}{\rho \sigma }}\,$, where $m_{p}=1.7\times 10^{-27}kg\,$ is the mass of a proton, $\rho =11000kg/m^{3}\,$ is the density of lead, and $\sigma \sim 10^{-47}m^{2}\,$ is the typical interaction cross section for a neutrino and a nucleon. The result is $L=1.5\times 10^{16}m\,$. That's 10 million times thicker than your million mile wide wall. Dauto (talk) 17:24, 2 November 2011 (UTC)

How about a neutron gas at 10 petapascals? It is still a gas under such low pressure right? Plasmic Physics (talk) 21:24, 2 November 2011 (UTC)

Rice and carbohydrates

I was wondering whether rice was made up of simple or complex carbohydrates or a mixture of both.122.63.93.9 (talk) 17:10, 2 November 2011 (UTC)

All rices contain a mixture of simple and complex carbohydrates (depending, of course, on how you define "simple" and "complex".) In general, the less "processed" the rice, the better balance of carbohydrates it will have. Brown rice will have the most fiber and other nutrients compared to more processed white rice. White rice is probably an order of magnitude even more nutritious (and tasty) than instant rice, which is (IMHO) a pretty worthless foodstuff; you might as well eat sawdust as far as I am concerned. There is also going to be some variation depending on which variety of rice you are eating; there are literally hundreds of different rice varieties, including things like Wild rice which, strictly speaking, is not rice but another variety of grass. I personally always cook brown rice, but that's because I prefer the texture and flavor more than white rice. --Jayron32 18:14, 2 November 2011 (UTC)

I concur

Are programmers different genetically?

What hypotheses, if any, posit differences between the consensus genome of the programming profession and that of the general population? NeonMerlin 18:16, 2 November 2011 (UTC)

There may be some differences; people's personality has a genetic component and personality is correlated to apptitudes and thus people will tend to do jobs which their personality and skill set and apptitudes tend to make them good at; since all of those sorts of things have genetic components, then there will likely be some general, statistical trends in terms of genetic similarities between people who tend to be programmers vs. everyone else. The same, however, could also be true for lots of people; I suspect one could find genetic similarities of the same type within firefighters or teachers or investment bankers. Which is not to say that every person in that profession will necessarily have that magic "programmer" gene, nor will everyone with said gene necessarily be a programmer (nor would they be good at it or even want to do it). These are likely very general, statistical averages. Remember also that there is always an environmental component to this as well, so people with the correct genes, but raised in a certain environment, may have no interest or skills in programming anyways. See nature vs. nurture --Jayron32 18:59, 2 November 2011 (UTC)

You might find more details in the journal Behavior Genetics.

—Wavelength (talk) 19:10, 2 November 2011 (UTC)

It's not at all clear if genetics are responsible, but I recall reading some studies awhile back saying that in high-tech areas like the Silicon Valley, the incidence of Asperger's and autism is considerably higher than the rest of the population. (A Wired story about this from about a decade ago.) Which is interesting on a number of levels. --Mr.98 (talk) 21:34, 2 November 2011 (UTC)

There are some cerebral changes associated with better linguistic skill. Dualus (talk) 22:42, 2 November 2011 (UTC)

But programming is not linguistics. It involves learning languages, but they are not as complex and variegated as natural human languages. Programming (in my experience) is more about analytical or logical articulation than it is about the language itself. --Mr.98 (talk) 00:22, 3 November 2011 (UTC)

Maybe computer science and related fields are the only place where aspies can flourish, hence the supposed high incident of them there. 88.9.210.218 (talk) 01:14, 3 November 2011 (UTC)

I don't think so. List of people with autism spectrum disorders suggests that people with Asperger sydrome have been successful in a wide variety of different fields. Gandalf61 (talk) 10:38, 3 November 2011 (UTC)

Definitely not "only", but the skill set required does work out pretty well for someone who is on that spectrum but still very high-functioning. Definitely more than, say, sales. --Mr.98 (talk) 11:44, 3 November 2011 (UTC)

Maybe a "geek gene"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:36, 3 November 2011 (UTC)

Identify atmospheric phenomenon

• 
  Picture 1
• 
  Picture 2

What is this atmospheric phenomenon seen at sunset on Interstate 135 near the Harvey/McPherson county line on October 6, 2011? Ks0stm ^{(T•C•G•E)} 22:45, 2 November 2011 (UTC)

Crepuscular rays? -- BenRG (talk) 22:53, 2 November 2011 (UTC)

Comment: these photos are shot through a car window. There's no telling what additional effect that glass had on the photo. Nimur (talk) 23:05, 2 November 2011 (UTC)

How do you know that it was shot through the glass of a car window? Bus stop (talk) 23:12, 2 November 2011 (UTC)

Because I stare at similar photographs all day long. Also, the captions state that they were taken on the interstate. Nimur (talk) 23:15, 2 November 2011 (UTC)

The glass had no effect, so far as I know. And there were no clouds that I could see, so I don't know for sure about them being meteorologically based crepuscular rays, and I have no idea what else could cause them in the middle of Kansas. Ks0stm ^{(T•C•G•E)} 23:19, 2 November 2011 (UTC)

If there's any haze or moisture at all in the sky, those sorts of contrasts can be visible as sunlight impinges on particulate matter or water-vapor. The darker areas may be places where the sun was shaded by the horizon. Nimur (talk) 23:21, 2 November 2011 (UTC)

Could they be shadows (and non-shadows) being cast by obstructions such as hills or large buildings that are below the level of the (apparently level) horizon? (Which would make them a form of crepuscular rays as linked by BenRG above, though not cast by clouds as is usually the case). Against this possibility, I'll agree that they appear suspiciously symmetrical. {The poster formerly known as 87.81.230.195} 90.197.66.254 (talk) 00:14, 3 November 2011 (UTC)

These are crepuscular rays, beyond doubt. 217.158.236.14 (talk) 15:11, 4 November 2011 (UTC)