# Homework Help: Help about gravitational force

1. Jan 21, 2004

### ACLerok

i am given a problem where a satellite in orbit is a certain distance from the surface of the earth. It then gives the radius of the earth. I realize i have to use the forumula: Fg=(Gm1*m2)/R^2
can i just use the distance from the surface of Earth to the satellite as R or do i add the radius of the Earth to it?

And also.. anyone kind enough to give me some hints on how to solve this simple problem??

Two uniform spheres, each with mass M and radius R , touch one another.
What is the magnitude of their gravitational force of attraction?

2. Jan 21, 2004

### discoverer02

R is the distance from the center of m2 to the center of m1, but if m2 is much, much larger than m1 (making m1 basically a point mass), then the distance from the surface of m1 to the center of m1 can be disregarded.

3. Jan 21, 2004

### FZ+

For all these problems, reduce the bodies to point particles at the centre of mass of the body. R would be the distance between the two CoMs. Then you do indeed need to add the radius and the height for R.

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