# Energy Conservation and Escape Velocity

1. Apr 29, 2004

If a particle is launched with kinetic energy as it gets further from the mass (eg a planet) the kinetic energy decreases. However Potential Energy GMm/r also decreases the further you get from the mass. Where does all this energy go?

Granted, the calculation U + K = 0 does give an answer that I have seen all over the place for escape velocity but I always thought energy is conserved and we have initial kinetic and potential energy but no final energy. I was wondering if energy is a vector quantity and there is no resultant energy.

Last edited: Apr 29, 2004
2. Apr 29, 2004

### arildno

It is negative potential energy that decreases in the escape velocity example, whereas kinetic energy is always a non-negative quantity.
Hence, in the escape velocity example, potential energy increases up to zero level as kinetic energy decreases to zero level.

3. Apr 29, 2004

I unterstand that potential energy is negative but I thought that was just convention. The size of the number is decreasing as you move away from a planet. So is the energy still not getting less as you move away?

4. Apr 29, 2004

### Janus

Staff Emeritus
Try thinking about it in terms of a debt. As the magnitude of your debt decreases, it is the same as gaining money.

5. Apr 29, 2004