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In g = GM/r^2 where r=0 where is this zero point interpreted to be? Is it at the surface of the sphere or the centre of gravity?

Quote from: jeffreyIn g = GM/r^2 where r=0 where is this zero point interpreted to be? Is it at the surface of the sphere or the centre of gravity?The relationship g = GM/r^2 refers to the gravitational acceleration given to a body which is located at a distance r from the body. The expression you wrote is incomplete because g is really a vector quantity. The correct expression would have a unit vector multiplying it whose direction is from the place the source is to the source point.The expression holds when the distance is very large compared to the dimensions of the source. If the distribution of matter is not spherically symmetric then that relationship is invalid when you're close to it. However if the body is a point object then the relationship holds no matter how close you are to it. If you’re too close though then you have to use Einstein's general theory of relativity.

Pete you have not answered the question at all. All I want to know is where the source is taken from.

Quote from: jeffreyHPete you have not answered the question at all. All I want to know is where the source is taken from.Sorry. I thought I was clear when I said the body was a distance which is located at a distance r from the body.You didnt' tell me anything about the source. That relation could hold for a point particle or for a spherically symmetric object. I any case the source object is centerred at r = 0.The source is located at

Is it at the surface of the sphere or the centre of gravity?

QuoteIs it at the surface of the sphere or the centre of gravity?For roughly spherical astronomical objects like planets, stars and interstellar dust, distance r is measured from the center of the sphere (providing r >> radius of the sphere).For a Plank mass whose quantum-theoretic uncertainty in position far exceeds the Plank length, measure r from the most likely point in the wavefunction.Good luck with your theory of quantum gravity!