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## Main Question or Discussion Point

I am hoping to get a deeper understanding of the difference between two different gravitational potential energy equations, the first of which is given by

and the second given by

I first assumed that in a system consisting of the Earth and, say, a tennis ball, these two equations would yield the same result for the potential energy of the tennis ball as it was held 1 meter above the ground. It another second or two to realize that the results of these two equations are

What is the explanation behind the difference in these two equations? What type of scenarios do each describe? Is it the fact that we are not considering the Earth itself as an object in the first equation? Is the second equation specifically describing gravitational force between two objects? Any insight on this would be very much appreciated!

**U = mgh**

and the second given by

**U = (Gm**

_{1}m_{2})/rI first assumed that in a system consisting of the Earth and, say, a tennis ball, these two equations would yield the same result for the potential energy of the tennis ball as it was held 1 meter above the ground. It another second or two to realize that the results of these two equations are

*extremely*different. This confuses me, since both equations describe "gravitational potential energy."What is the explanation behind the difference in these two equations? What type of scenarios do each describe? Is it the fact that we are not considering the Earth itself as an object in the first equation? Is the second equation specifically describing gravitational force between two objects? Any insight on this would be very much appreciated!