Gravitational Potential Energy of an object of mass

AI Thread Summary
The discussion clarifies that in the formula for gravitational potential energy (GPE = -GMm/r), the variable r refers to the distance from the center of a spherical mass M, not from its surface. This applies specifically when dealing with spherically symmetric mass distributions, such as the Earth, Sun, and Moon, allowing them to be treated as point masses. Participants confirm that the formula for gravitational potential energy uses r, not r², distinguishing it from gravitational force calculations. The emphasis is on the importance of understanding the correct application of the formula in relation to mass distribution. Accurate interpretation of these concepts is crucial for physics applications.
nathangrand
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Does the r in GPE=-GM/r refer to the distance an object is from the centre or surface of the object of big mass M?
 
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nathangrand said:
Does the r in GPE=-GM/r refer to the distance an object is from the centre or surface of the object of big mass M?
The center. (And that should be GPE = -GMm/r; you left off the mass of the object.)
 
Well to be more exact it's the distance between the centers of the two objects.
 
Its the distance from the centre of the big object as long as the big object is spherical. (Which luckily the earth, sun and moon roughly are).
 
BruceW said:
Its the distance from the centre of the big object as long as the big object is spherical. (Which luckily the earth, sun and moon roughly are).
Right. It requires a spherically symmetric mass distribution, which allows us to treat a large mass as a point mass.
 
Is it not r2 in the above formula?
 
JaredJames said:
Is it not r2 in the above formula?
No. It's for gravitational PE, not force.
 

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