- #1
zinc79
- 9
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Hello. I'm new. I was looking around on the web a bit to find an answer to my problem, and I came across these forums.
Gravitational force = -GMm/(r^2)
Gravitational force between a small mass (m) and the Earth (M) is zero at a distance of infinity. Any distance smaller than infinity gives a negative value. When the distance is minimum, the force is mathematically minimum but actually the largest in magnitude. When the distance is infinite, the force is mathematically largest but actually the least in magnitude.
But what is gravitational potential energy? Is it work done due to gravitational force in moving a mass from a distance (r) to an infinite distance? Is it work done due to gravitational force in moving a mass from a an infinite distance to a distance (r)? Or is it simply the work done due to gravitational force in moving the mass from one point to another?
Now, I'll deal with a case when I move a mass (m) from a distance (r1) to an infinite distance from the Earth (r2)
The gravitational potential energy, as I have learnt, is simply the integration the the gravitational force. This comes out as GMm[(1/r2) - (1/r1)]. This is where I have the problem. If the mass gains height, i.e. moves away from the earth, then r1 is small and r2 is large, and because of this the gravitational potential energy turns out negative! Isn't it supposed to be a GAIN in potential energy? Isn't the change supposed to give a positive value? If not, then why? Work is being done ON the object to raise it, right?
Gravitational force = -GMm/(r^2)
Gravitational force between a small mass (m) and the Earth (M) is zero at a distance of infinity. Any distance smaller than infinity gives a negative value. When the distance is minimum, the force is mathematically minimum but actually the largest in magnitude. When the distance is infinite, the force is mathematically largest but actually the least in magnitude.
But what is gravitational potential energy? Is it work done due to gravitational force in moving a mass from a distance (r) to an infinite distance? Is it work done due to gravitational force in moving a mass from a an infinite distance to a distance (r)? Or is it simply the work done due to gravitational force in moving the mass from one point to another?
Now, I'll deal with a case when I move a mass (m) from a distance (r1) to an infinite distance from the Earth (r2)
The gravitational potential energy, as I have learnt, is simply the integration the the gravitational force. This comes out as GMm[(1/r2) - (1/r1)]. This is where I have the problem. If the mass gains height, i.e. moves away from the earth, then r1 is small and r2 is large, and because of this the gravitational potential energy turns out negative! Isn't it supposed to be a GAIN in potential energy? Isn't the change supposed to give a positive value? If not, then why? Work is being done ON the object to raise it, right?