Posted by **Kathrine** on Wednesday, December 17, 2008 at 7:58pm.

How is it possible for gravitational potential energy to be negative?

I Googled the answer, but all I could understand was that if the PE was zero at infinity as you move toward an object with gravity the KE must be positive because KE is the energy of motion so the the PE must be negative to equal a total of zero. Is this right? Or am I way off the mark?

- Physics -
**bobpursley**, Wednesday, December 17, 2008 at 8:01pm
PE is always to a reference. It is zero at infinity. But we commonly set some place (say ground level) and measure GPE in relation to that plane. Negative GPE means energy has to be given to get it back to zero. Example: refernce level is at 12 feet above ground. Below that, GPE is negative.

- Physics -
**Kathrine**, Wednesday, December 17, 2008 at 8:13pm
Okay, so using the ground level for your reference point if you went under the crust the GPE must be negative for the total energy to remain zero?

I think I get it! Thanks a lot!

- Physics -
**bobpursley**, Wednesday, December 17, 2008 at 8:13pm
That is it.

- fgox oilx -
**fgox oilx**, Saturday, January 17, 2009 at 2:45am
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