# Ball rolling down a frictionless plane?

1. Nov 5, 2008

### physics_liker

1. Under all ordinary conditions, would a ball released from rest start rolling down a frictionless inclined plane with just the force of gravity pulling it down? Or is it really just going to slide down?

Now let's suppose a gigantic ball released on the slope of an enormous frictionless inclined plane, so that the gravitational force varies considerably from the bottom to the top of the ball? What would happen? Would the ball then start rolling?

Thanks.

2. Nov 5, 2008

### mgb_phys

The answer is yes - now have you learnt anything ?
Perhaps you could draw a diagram of the forces and see if that helps?

3. Nov 6, 2008

### physics_liker

I am sorry. Can you be more specific as to which answer you responded yes? I had two situations. I only want to hear what others think so that I can verify my own answers. Thank you for responding.

4. Nov 6, 2008

### mgb_phys

When you posted the question you deleted a template stating that you have to show your attempt. You can google the answer (it's a well known example) the point here is to learn something.

Your second part- no - there is a general principle of gravity that you can replace any object with a point mass at it's centre and have the same effect. So the difference in gravity between the top and bottom of a ball wouldn't matter

5. Nov 7, 2008

### Staff: Mentor

What's required to make a ball roll instead of just slide?

6. Nov 7, 2008

### physics_liker

First I thank your responses. To mgb_phys: I have googled this answer for lots of times; the only satisfactory answer came from wikianswers. I only wanted to make sure this is really the case. To Doc Al: Friction.

I guess I am going to think about this problem a bit more.

7. Nov 9, 2008

### Staff: Mentor

This is true, so that should answer your question.
You never said what you thought the answer was or why.