Question about spheres in rotation
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01-08-2011, 12:56 AM
RE: Question about spheres in rotation
The farther you are from the core, the lower effect gravity will have. Even though the distance change is a "trivial" 40 km, the distance has a much greater impact on gravitational strength then mass, because its being squared.

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01-08-2011, 01:35 AM (This post was last modified: 01-08-2011 01:57 AM by DeepThought.)
RE: Question about spheres in rotation
No need to repeat yourself. I understand that.

I'm talking about density. If you cut earth into small chunks and put all the core and heavy stuff on the opposite end of the planet and all the water and air and lighter crust elements on this side then you will get a radically different gravitational pull from the different configuration.

Those highschool equations talking about distance from the 'core' are really oversimplified. Every atom on this planet participates in the gravitational interactions. The air above you is counteracting Earth's pull on you by a minuscule amount.

The amount of that pull depends on the mass of those elements.

If you had a mountain made of lead the size of mount Everest and you burrowed underneath it right to the center at sea level you would experience significantly less gravity there. You might even be close to weightless though I haven't done the calculations...
Wikipedia Wrote:Local variations in topography (such as the presence of mountains) and geology (such as the density of rocks in the vicinity) cause fluctuations in the Earth's gravitational field, known as gravitational anomalies. Some of these anomalies can be very extensive, resulting in bulges in sea level, and throwing pendulum clocks out of synchronisation.
The study of these anomalies forms the basis of gravitational geophysics. The fluctuations are measured with highly sensitive gravimeters, the effect of topography and other known factors is subtracted, and from the resulting data conclusions are drawn. Such techniques are now used by prospectors to find oil and mineral deposits. Denser rocks (often containing mineral ores) cause higher than normal local gravitational fields on the Earth's surface. Less dense sedimentary rocks cause the opposite.

So with that in mind:
If all of earth had uniform density (mass per unit volume) How would that effect gravity? Note that the bulge only accounts for 40km... Trivial compared with Earth's the total diameter.

“Forget Jesus, the stars died so you could be born.” - Lawrence M. Krauss
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01-08-2011, 03:24 AM
RE: Question about spheres in rotation
The earth can't have uniform density, humanity depends on the variations.

Air exists above the surface because its less dense and therefore exists above the more dense crust.

Think about water. Anything with more density then water sinks below it, anything with less density will float on top. The same thing happens to solids and gases, the less dense air (oxygen dissolved in nitrogen) along with carbon dioxide, helium, etc are less dense than rocks and sediment, which is less dense then the mantle, which is less dense than the core.

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04-08-2011, 09:22 PM (This post was last modified: 04-08-2011 09:43 PM by DeepThought.)
RE: Question about spheres in rotation
I am aware of that. I was creating an ideal scenario for simplicity. High school physics only gets you so far...

http://en.wikipedia.org/wiki/File:GRACE_...mation.gif

The gravitation values at the equator and the poles in my 6th post were averaged. If you look at the map you'll find the reasons for the differences in gravity does not have much to do with the extra 20km distance from the center of the earth. There are many areas on the equator (areas on land) where there is a stronger gravitational pull than on the poles.

Also - Your distance from the center of an object in a simple model is irrelevant when you are standing on the surface of that object. If you make a simple model of uniform density like a ball of putty - make it the shape of a discus. Imagine earth was the shape of a discus.

[Image: 30886867-60x60-0-0_Nelco+Nelco+2K+Indoor+Discus.jpg]
The gravitational pull would be strongest if you were standing on the area furthest from the center. If you were standing on the poles gravity would be weakest.

This is a massive exaggeration compared with earth since the radius is ~6378km and the equatorial bulge only accounts for a 20km variation. This is trivial.

“Forget Jesus, the stars died so you could be born.” - Lawrence M. Krauss
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07-08-2011, 12:17 PM
RE: Question about spheres in rotation
i dunno

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