Rotation About a Vertical Axis?

Question

How's this sound?

A beetle sits near the rim of a turntable that is at rest, but is free to rotate about a vertical axis. What happens if the beetle begins to walk around the perimeter of the turntable? Does the beetle move relative to the ground? Consider the limits of a very massive turntable and a very light turntable.

Yes, the beetle moves relative to the ground. Because to every action, there is an equal and opposite reaction (Newton’s Third Law), the table would try to turn in the opposite direction. If it is a very light turntable, we would be able to see some motion, but not for a heavy one.

Answer 1

If there's no friction and we're considering of only a system of a turn table and a bug walking along the edge of disk, then you just have to conserve angular momentum of the system. A light bug on a heavy turntable would see the bug move a lot relative to the ground and the turntable turn very slowly in the opposite direction. A heavy bug on a very light turntable would see the bug move very little but the turntable turn a lot. The sum of angular momentum of the turn table and the bug has to add up to zero.