Mechanics:
Pulling on a Whirligig

Purpose:
To demonstrate conservation of angular momentum as the distance to the rotation axis changes.

Description:
Hold the metal tube and swing the ball in a circle at a speed/radius such that the hanging washer is just supported (i.e. it's weight provides the centripetal force). Stop actively swinging and use your other hand to pull down on the string shortening the radius of rotation and observe the change in rotational speed.

Equipment:
Ball on a string