• A ring and some string
When an ice skater spins with outstretched arms, then quickly lowers her arms, her speed of rotation increases enormously. This is because her arms are suddenly forced to move in a smaller circular path. This effect can be demonstrated with a finger ring and a piece of string. Attach the string to the ring so that it hangs down, as in the illustration, while you hold the ends of the string. Now twirl the ring in a circle about six inches (15 cm) in diameter. As you twirl the ring, pull on the ends of the string. The ring speeds up.
HOW DOES IT WORK?
When the ends of the strings are pulled, the ring is forced to go around in a smaller circle, causing its angular velocity to increase suddenly. Much the same thing happens when water goes down the drain of a more...