Lester and Phoebe have a contest to see who can rotate an apparatus the fastest. The two apparatuses weigh exactly the same, but Phoebe wins because the weights on hers are closer to the middle. This demonstration explains how figure skaters can spin faster when they pull their arms and legs inward.
Bill explains how we measure time and mentions some of the tools we use to measure it. He notes that time measurements, such as days, months, and years, are based on astronomical events and uses a motion machine to illustrate the Earth's revolution around the Sun and the Moon's revolution around the Earth.