As usual I enjoyed Paul Hewitt’s “Figuring Physics: Water Roll” [Phys. Teach.57, 131 (March 2019)]. For many years we have combined the rolling cylinders problem into a single racing demo.

The finish line on the floor was placed some distance from the base of the inclined plane. Using a can of Coke and a solid aluminum cylinder about the same size of the Coke, we would ask for bets on the winner. With a few tries before class we could determine the place where the finish line would produce a “tie.” Then for a shorter distance the Coke would win and for a longer one the aluminum would win. We controlled the winner!

As an additional demo we used two identical Cokes labeled A and B. Of course they would tie at the bottom of the inclined plane. But, if you shake A vigorously, B will...

AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.