# Question about gravity's effect on moving bodies

1. Jul 10, 2014

### Veridian

I have a question about gravity and the way it interacts with moving bodies. Let's say gravity was the surface of a very stretchy fabric. You take an object like a marble and roll it across an infinite plane of this fabric. The fabric causes the object to lose energy because of friction. My question is: does gravity work the same way? Does gravity cause objects to lose energy because of 'friction'?

2. Jul 10, 2014

### Staff: Mentor

No. If gravity caused a sort of friction then you would have a preferred frame, the frame in which it eventually would come to rest.

3. Jul 10, 2014

### HallsofIvy

Staff Emeritus
There's your first problem- it's not!

4. Jul 10, 2014

### Nathanael

It helps to look at things in various ways, even if it's not always right.

When you say "lose energy" I assume you mean kinetic energy?

If this were the case, wouldn't you expect planets to spiral into the sun? Earth would have been getting closer and closer to the sun over it's lifetime.

The thing about energy lost to friction is that the energy goes somewhere (mostly to thermal energy).

Your picture is only half of a picture, you would need to imagine something for the energy to be transferred to (or else you're challenging conservation of energy).