Ball on string orbits with increasing speed as string is shortened.
What it shows:
An object moving in a circular orbit of radius r has an angular momentum given by:
L = r × mv = mr2ω.
A simple way to show conservation of angular momentum is a ball on a string, whirled around your head. As you change the length of the string, the ball's orbital speed changes to conserve angular momentum.
How it works:
The orbiter consists of a meter length of cord with a wooden ball at one end and a wooden anchor at the other. The cord passes through a ballpoint pen casing. Swing the ball around your head holding the pen casing, using the other hand to hold the anchor so as to maintain or adjust the active length of cord.
Good accompaniment to the Three Dumbells.