# Gravitational energy?

1. Nov 14, 2005

### underworld

Let's see if I can articulate this question the way that I'm thinking about it....

Imagine you have a big star (like the sun)... and every so often a comet or meteor (or even several of them) whiz past. My understanding is that the star's gravity will influence the path of the comets and/or meteors, right? Ok - that's the simple part.

Now - am I correct in assuming that it takes energy to influence the path of the comet or meteor? I would think yes - otherwise the comet would continue on its merry way in its current direction. Just to rephrase:

Question 1) Does it take energy for a larger body to influence (gravitationally) the path of a smaller body?

Next point - am I correct in assuming that the energy has transferred from the star to the comet? I think the answer is yes since the comet could easily be observed to change its path. So:

Question 2) Is there an energy transfer between two bodies during gravitational attraction?

Now my final point - which is a little weird - if the above assertions are true - then what happens when a large number of comets and meteors pass by the star? Does each use up a little of the star's energy? And, perhaps more interestingly, does a single object which repeatedly uses a star's energy (such as a smaller body in orbit) continuously use up that energy?

Question 3) Will continuous energy transfer due to gravitational attraction eventually deplete the energy of a body?

The only answer I can come up with is that there is an energy transfer, but it somehow occurs bi-directionally. I.e. as the star's energy is used to alter the path of the meteor, somehow that energy is returned back to the star during the process - but I have no idea how or why that would occur.

I'm sure there's a simple explanation for this. I imagine the same questions apply to natural magnets....

Any thoughts on this would be greatly appreciated....

2. Nov 14, 2005

### Staff: Mentor

1. Yes.
2. Yes.
3. No. This energy is gravitational potential energy, being converted to kinetic energy, and conservation law applies: the net energy change of the system is zero. How? When a comet passes a star, the comet's path is altered, but so is the star's. (your instinct was correct)

3. Nov 14, 2005

### underworld

so, does the light that is bent by a large body also alter the path of the large body?

for example, if you had access to enough energy, could you focus a large amount of light to pass by a meteor and alter the meteor's path? (ok, maybe that's far-fetched - but I'm working with the conceptual here...)

4. Nov 14, 2005

### Macro

Space-time curvature is not energy.
The energy of a falling object remains the same.
General Relativity is about conservation of energy.
Where time goes slower the objects speed up to
conserve their total energy.
Einstein described this interchange.

Mitch Raemsch -- Light Falls --