Nice one Marchimedes. I don't have much time right now, but I noticed a couple of questions.

One was about gravitational attraction over various distances. There's a law of classical physics about that:

It's called Newton's Inverse Square Law. On your drawing it means that at

(2) the gravitational attraction is 1/(2^2) of the gravitional attraction at (1) - that's a quarter
(3) the gravitational attraction is 1/(3^2) of the gravitional attraction at (1) - that's a ninth
(4) the gravitational attraction is 1/(4^2) of the gravitional attraction at (1) - that's a sixteenth

The speed of gravity is c (the speed of light). It's normally referred to as the speed at which gravity propagates, but it still means the same thing smile

So, if by some trick the sun was removed to a parallel universe, the Earth would still continue in its orbit for about 8 minutes, then it would shoot off at a tangent. At the same moment, we would see the sun disappear. Meanwhile, Mars would continue in its orbital path for another 4 minutes. Then it too would shoot off. Jupiter would continue to orbit the non-existent sun for another half hour!
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So, the gravitational attraction of an object is proportional to its mass and its distance; if you're standing on a planet with twice the mass of Earth you won't be twice as heavy unless the radius is the same. The effects of the gravity at the surface depend on the distribution of the mass, and in this case the radius of the planet.

Here's is one I made earlier (as they say on the cookery programs):

Acceleration due to gravity:

g = G(M/r^2)

where
g = acceleration due to gravity (m/s2)
G = universal gravitational constant (m3/kg/s2) = 6.673*10^-11
M = mass of the body (kg or slug)
r = radius of the body (m or ft)
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For Earth:

g =(6.673*10^-11)*((5.98*10^24)/((6.375*10^6)^2))= 9.81
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For Gliese 581 c: (a recently discovered Earth-like planet)

If it has 4.83 x Earth mass, and a radius of 1.5 x Earth then:

g =(6.673*10^-11)*(((5.98*10^24)*4.83)/(((6.375*10^6)*1.5)^2)) = 21.1

21.1/9.81 = 2.15 x Earth gravity.

You might have thought that the gravitational attraction at the surface would be 4.83 x as great, but it's only 2.15 x.

This might be useful: http://www.qrg.northwestern.edu/projects...ts-gravity.html

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"Time is what prevents everything from happening at once" - John Wheeler