# Homework Help: Gravitational potential

1. Dec 26, 2008

### nokia8650

The image below shows a sketh of gravitation potential (y axis) vs. position:

http://img175.imageshack.us/img175/5717/60413547vb3.th.jpg [Broken]

Can someone please explain why the potential does not equal zero at the neutral point - wouldnt the two potentials cancel each other out?

Thanks

Last edited by a moderator: May 3, 2017
2. Dec 26, 2008

### D H

Staff Emeritus
First off, why would you expect it to go to zero? That plot is of

$$u(r) = -\left(\frac{GM_e}{|r|} + \frac{GM_m}{|R_m-r|}\right)$$

That function is negative definite: its value is negative for all finite values of r.

Secondly, what do you mean by "neutral point"? This term has multiple meanings.

3. Dec 26, 2008

### tiny-tim

Hi nokia8650!

Where is the potential being measured from (in other words, where is zero potential)?

Potential is often measured "from infinity" …

in that case, the potential will only be zero at an infinite distance from both the Earth and the Moon.

Last edited by a moderator: May 3, 2017