[ExI] A Lawn sprinkler

[John K Clark]

You pump water through an S shaped lawn sprinkler and it spins
counterclockwise, but suppose you put the sprinkler in a tank of water and
pump water out not in. What direction will the sprinkler rotate? As an
undergraduate Richard Feynman actually tried the experiment but he was not
successful; the tank burst flooding the lab and he almost got kicked out of
school. However he later figured out what the answer must be.

 John K Clark