# Zero Normal force during uniform circular motion?

1. Jun 23, 2011

### soominds

I am learning uniform circular motion and the question says: A child on a sled comes flying over the crest of a small hill. His sled does not leave the ground but he feels the normal force between his chest and the sled decrease as he goes over the hill. Explain.

Now, I know that normal force decreases at the crest of the hill as there is downward centripetal force. But how exactly does it 'feel' when the normal force decreases/ goes to zero? Do you become air-borne? Shouldn't the sled be penetrating the hill since the weight is now greater than normal force?

Sincerely,
Confused student.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 23, 2011

### tiny-tim

welcome to pf!

hi soominds! welcome to pf!
no

there is no such thing as https://www.physicsforums.com/library.php?do=view_item&itemid=529"

there is https://www.physicsforums.com/library.php?do=view_item&itemid=84" (in the reference frame of the child)

and there is https://www.physicsforums.com/library.php?do=view_item&itemid=27" (in the stationary reference frame)

which frame does your professor want you to use?​

Last edited by a moderator: Apr 26, 2017