  A bouncing rubber ball under a motion sensor is a classic of introductory
physics labs. It is often used to measure the acceleration due to gravity, and
can also demonstrate conservation of energy. By observing that the ball rises
to a lower height upon each bounce, posing the question "what is the main
source of energy loss?" and requiring students to construct their own measured
values for velocity from position data, a rich lab experience can be created
that results in good student discussions of proper analysis of data, and
implementation of models. The payoff is student understanding that seemingly
small differences in definitions can lead to very different conclusions.
