Do-it-yourself: centripetal force

This device demonstrates centripetal force. Just hold it vertically and whirl it gently so that the top weight circles around. Speed up the motion and the bottom weight rises as the centripetal force increases.

I used a pair of old keys as weights. Takes a bit of practice but is easy enough.

Materials: drinking straw, sewing thread, two weights. A glass tube or plastic tube should also work instead of the straw.