# Quick question about a man running on a Merry-go-round

1. Feb 19, 2016

### ecoo

Hey there,

If a man is on the edge of a carousel and starts to run perpendicularly to cause a torque on the carousel (no friction on axis of rotation), will the man be running in place? And if he is running in place, how is rotational momentum conserved of the man-carousel system?

I think that the man will run in place, and so I'm not sure how rotational momentum is conserved.

Thanks!

2. Feb 19, 2016

### ecoo

The reason I am confused about the conservation of rotational momentum is because if the man is running in place and not moving, then only the carousel will be turning and so there will be rotational momentum, whereas initially there was none when both the man and carousel were at rest.

3. Feb 19, 2016

### A.T.

Will it be turning at the same rate?

4. Feb 19, 2016

### billy_joule

That is only true for a special case....
And in that case the carousel has no rotational inertia...
draw a free body diagram and apply Newtons laws.
Consider the two special cases; where the carousel has infinite mass and where it is weightless