Bill S.
I wish you wouldn't ask things like that, it makes me have to think. Not my most favorite thing to do. But then I have to go ahead and try to answer. You may be aware that graduate students are required to teach a number of courses in their discipline. One reason for this is that the university gets cheap teachers. But one other reason is that teaching a course makes you actually think about what you have learned. When you get so you can explain it to others you have a pretty good handle on the material yourself.
Who said that gravity isn't a force? Well, in a way Einstein did. He said that gravity is the result of warped space. Let me think how to say this. To us gravity appears as a force. This is because in general things try to get to the lowest energy level. A massive object creates a warp that has its lowest energy at the center of the mass, so that anything entering the area of warpage will try to get to the center of the mass. This is the same as the way your car will roll down a hill if you park it with the brakes off and the transmission in neutral. The steeper the hill, the faster it will roll. So the deeper the gravity well, that is the more massive the object, the steeper the slope of the warp. The slope of course isn't constant, it varies inversely as the square of the distance between the objects. That's why gravitation "force" varies with distance.
As far as the GPE (gravitational potential energy) of an object from space is concerned, the initial example was a stone raised from the surface of the Earth, GPE doesn't really require that the object be raised from the Earth. GPE is really the amount of energy that the object can gain in falling to the Earth.
Hope this helps.
Bill Gill
