Wikipedia:Reference desk/Archives/Science/2013 December 28

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December 28

Gravity

What is gravity? Like what forms it? How does an object create gravity? Does any object have its own gravity? 139.193.132.190 (talk) 00:09, 28 December 2013 (UTC)

The word "gravity" means "heaviness". I recommend you start with the Gravity article and see where it takes you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:18, 28 December 2013 (UTC)

Those are big questions, and no one knows for sure, but Bugs' suggested the Gravity page. His description of "heaviness" is a very basic approximation, but it's as good as any to start. More specifically, it is a force that makes things attracted to each other. The obvious one is people not floating off into space from the Earth. The confusing part is that it goes both ways: People attract the Earth to them, too, but we are so miniscule that the force basically doesn't matter. The last question is the easiest, though: yes, every object "has its own" though some speculate that there may be particles and stuff that doesn't. Nothings been proven yet. Mingmingla (talk) 01:31, 28 December 2013 (UTC)

You might try: Andrew Zimmerman Jones and Daniel Robbins. "Einstein's General Relativity Theory: Gravity as Geometry". For Dummies. InsideDummies.com.

And this video clip: From the NOVA PBS series THE ELEGANT UNIVERSE, host Brian Greene guides us through Einstein's explanation of gravity. ~E:71.20.250.51 (talk) 01:37, 28 December 2013 (UTC)

• If you can figure out why inertial mass is (or is not necessarily) the same thing as gravitational mass, you'll win the nobel, and go down in history with Newton and Einstein. μηδείς (talk) 03:42, 28 December 2013 (UTC)

• • Except, Einstein already did just that some 100 years ago. See general relativity and equivalence principle. Oh, and he won the Nobel. But not specifically for that. --Jayron32 05:35, 28 December 2013 (UTC)

I thought he proved that it is the same. I didn't know he had the full explanation why. 75.75.42.89 (talk) 06:24, 28 December 2013 (UTC)

What do you mean by "why?" That matters when answering a question like this. A whole lot. --Jayron32 06:53, 28 December 2013 (UTC)

Ultimately science doesn't answer "why" questions. The best it can do is say "Why does A happen ? Because of B". If you ask why B happens you might get a C, but eventually you will run into a "nobody knows why" answer. So, it's really the same as the turtles all the way down problem religion has. StuRat (talk) 15:49, 28 December 2013 (UTC)

Here we are on the 101st floor, Stu and co. have been down to the 77th, and they assure us it's stairwells on top of stairwells, to infinity? μηδείς (talk) 18:51, 28 December 2013 (UTC)

Alas, I will never understand why people say general relativity is "elegant." I've never seen such messy equations! Every parameter affects every other parameter; all the terms are 12-element tensors; it takes two pages to write "simple harmonic motion" and two more days to solve it... and the answer is neither simple nor harmonic... about the only way to write the darned equations is to abbreviate everything so compactly that you don't actually have to see any of the terms that are either generalized or relativistic. Why do people keep saying it's so wonderful? Probably because they've never tried to use it! I've seen generalized theories of transistor saturation current that are more "elegant!" Nimur (talk) 16:08, 28 December 2013 (UTC)

One way I like to think of it (in a "General" sense) is to think of the 3-D representation of a 4-D phenomenon (a bowling ball on a rubber sheet, roll a ping-pong ball around in "orbit"), in the same way you can represent a 3-D phenomenon (let's say an elephant) in a 2-D representation (a picture). Anyway, if you figure out all there is to know about gravity, be sure you publish it before you float off into the infinite void. ~E:71.20.250.51 (talk) 09:47, 28 December 2013 (UTC)

Gravity is related to mass. A particle`s mass in physics is the same as (equivalent) its energy. In electro-magnetism a current of electricity causes (induces) a magnetic force field, that makes metal being attracted. In ferro-magnetism (e.g. permanant metal magnets) it is the particle`s charge causing the attraction of (other) metal (or other magnets according to their poles). Science does not know which sort of °charge° in particle`s mass-energy or any other cause causes massive objects to attract one another no matter which particles they consists of - actually, even light is attracted by big masses on huge scales (supposedly by its mere mass-equivalent energy? gravitational_lens), even though it (science) understands thoroughly the effects and their sublying law of nature (Newton; Einstein, ART). afaik We also don't know, if there is actually a force field transmitting[?] how gravity transmits .. with lightspeed or if gravity is a geometric property of mass or the spacetime around it (gravity then being instantaneous phenomenon without transmission); but observations of double pulsar PSR_B1913+16 seem to indicate, that gravitation is being transmitted by a force field[?] with a speed (by a gravitational force field? gravitons?).

Maybe masses are simply not meant to being separated from one another, since originally being lumped up in one before bigbang. O.-o --217.84.64.106 (talk) 20:31, 28 December 2013 (UTC)

Isn't it the other way round: in Newtonian Mechanics, gravity is assumed to be instantaneous, but in General Relativity it is shown to propagate at the speed of light? The double pulsar decay observations suggest that the speed of gravity is within 1% of the speed of light if General Relativity is an accurate model of the universe. Dbfirs 20:56, 28 December 2013 (UTC)

[I didn`t say "newtonian force field", but I´m not sure about force fields and I meant emphasis on "instantaneous or not", so I barred above. -- 217.84.aso] --217.84.73.254 (talk) 19:07, 29 December 2013 (UTC)

The speed c for gravitational waves is a small-signal approximation for a mostly-flat universe (i.e., mostly Newtonian!) The wave equation for the gravity metric in general relativity is ill-defined if the curvature is large, because it becomes unclear which coordinate system should be used to apply the derivatives in time and space - crucial to the wave equation. Our article uses a spatial derivative and time derivative in flat space to derive a wave; but in flat space, there is no mass, and therefore no wave! So clearly this model breaks down somewhere. Earlier this week, another question was asking about incompleteness in modern physics theories... well, there's one! In general, full form, Einstein's equations for gravity are unstable. Disturbances (waves) propagate at an indeterminate velocity, and they grow without bound. That seems like a small problem to me! It's exactly the reason you'll find "perturbation theory models" described in all our articles about gravitational waves: they assume the initial solution is stable, and study tiny variations. Nimur (talk) 15:36, 29 December 2013 (UTC)

Water Salinity reduction using Salt Water Pool Chlorinators.

If I pass brackish water through a chlorinator unit (as used in swimming pools), will the salt content of the water be reduced? If yes, is there a method of working out the reduced salt in water? — Preceding unsigned comment added by 120.145.132.81 (talk) 06:58, 28 December 2013 (UTC)

No, all that the chlorinator will do is add chlorine to the water, it won't remove salt. See Desalination and Water chlorination for the relevant articles. Tevildo (talk) 15:05, 28 December 2013 (UTC)

The English version of Wikipedia serves many countries, each with their own understanding of technical terms. When you say chlorinator unit do you mean a contrivance that meters out sodium hypocrite or one that injects chlorine gas or a salt-water-chlorine-generator?--Aspro (talk) 15:07, 28 December 2013 (UTC)

With the salt-water-chlorine-generator it will convert salt to chlorine and err.. I think sodium... something or other – blast! I don't think the the compound coming into to my head is right but it might sodium hydroxide (it is still Christmas where I am and the festive spirit (or rather a lot of single-malt whisky (no 'e' after the k) has temporally disconnected my long-term archival hard drive memory. Yet, it is something along those lines. Me thinks, Christmas should be held like the Olympics, one every five years. My bank balance hardly recovers from the last festive season when 'bang', it's upon me again. I think, I will retire to my shed at the bottom of the garden, until this merriment is all over.--Aspro (talk) 15:29, 28 December 2013 (UTC)

If you think the Olympics are held every 5 years, I bet you showed up VERY late for them. StuRat (talk) 15:42, 28 December 2013 (UTC)

It's not totally clear Aspro is showing up for the olympics as opposed to simply celebrating them. If they try to celebrate them every 5 years, I guess this means they actually only get to celebrate them every 10 years presuming they are including both the summer and winter Olympics or 20 years presuming they only mean the summer. Either way, since one of Aspro's complaints is too frequent celebration, this is probably a good thing. Alternatively I guess this may be an indication Aspro's archival hard drive memory is more disconnected than thought or that Aspro doesn't actually need a reason for merriment or realise that they're the only one doing it once started. Nil Einne (talk) 16:21, 29 December 2013 (UTC)

But he's given me a great idea for a new invention: a machine that removes the excess sodium hypocrite [sic] from politicians, priests, parents and purveyors of platitudes. -- Jack of Oz ^{[pleasantries]} 17:53, 29 December 2013 (UTC)

Wouldn't a sodium hypocrite be a person who tells others to cut back on their salt, but uses a lot themself ? StuRat (talk) 19:01, 30 December 2013 (UTC)

Of course, adding chlorine will itself dilute the salt by a trivial amount, assuming the amount of chlorine is far less than the amount of water. (That is, if you define the salinity as the amount of salt relative to everything else, not just relative to the amount of water.) StuRat (talk) 15:52, 28 December 2013 (UTC)

Nobody has yet pointed out our salt water chlorination article? DMacks (talk) 07:30, 30 December 2013 (UTC)

Lorentz force helix

I have a few questions about the Lorentz force.

1. Is it possible to create a Lorentz force helix in a cloud chamber and if so how would this be achieved?

2. How would the pressure inside the helix be measured in comparison to the pressure surrounding the helix?

3. Is there a limit on how much pressure the helix could produce? Ultimately what I am asking is, whether it is possible to create mini tornadoes and for those tornadoes to support a payload.

Thank you — Preceding unsigned comment added by Aussietaurus (talk • contribs) 17:31, 28 December 2013 (UTC)

Have you considered a solenoid carrying a time varying current? You will need some charged particles to be affected by it though. Graeme Bartlett (talk) 07:57, 29 December 2013 (UTC)

Lack of sebaceous glands on palms of hands and soles of feet

According to our sebaceous gland article, they aren't present in those locations. So then, what keeps those areas from drying out ? StuRat (talk) 21:42, 28 December 2013 (UTC)

Sweat glands, specifically Eccrine sweat glands - note: there are more on palms than on backs of hand ( ~370 sweat glands per cm² vs. ~200 per cm²); our article doesn't mention feet. ~E:71.20.250.51 (talk) 21:59, 28 December 2013 (UTC)

But I wouldn't expect sweat glands to do much good, since saltwater does tend to dry things out as soon as it evaporates, leaving a salt residue. StuRat (talk) 07:53, 29 December 2013 (UTC)

Also note that even amimals without sweat glands don't "dry out", presumably due to circulatory system and osmosis. ~:71.20.250.51 (talk) 22:03, 28 December 2013 (UTC)