# Gravitational potential energy

1. Dec 16, 2007

### heinrich

if we think the height of a matter reaches over the radius of the earth how will the potential energy of it change?
when height of it approaches infinite from zero how will be the graph of gravitational potential energy-height?
thank you

2. Dec 16, 2007

### Staff: Mentor

Is this homework? Do you know the equation for potential energy? Graph it!

edit: actually, since g changes with distance for large distances, you'll want to insert the equation for g into it.

Last edited: Dec 16, 2007
3. Dec 22, 2007

### Shooting Star

Somehow I don't feel this was a HW question.

The PE of the earth's grav field is -GM/r, where r is the dist from the centre. As r increases, GM/r decreases, and so -GM/r increases. As r tends to infinity, the PE tends to zero, which is the maximum value, through negative values, .

The graph between PE and r is a rectangular hyperbola.

4. Dec 23, 2007

### granpa

the law of conservation of energy states that energy is never created or destroyed. it just changes from one form to another. good thing they invented negative energy to rescue this rule.

5. Jan 23, 2008

### Shooting Star

Actually, it sort of got invented by itself, when we called pull a negative push.

6. Jan 25, 2008

### sandoko

i agree with shooting star....you can easily see it from the work energy theorem...