30. Things Are Not What They Seem

a. Unpredictable discs
Ask the class which of two identical looking discs will roll down an inclined plane the fastest. Most students will say they will roll equally, but one rolls down, and the other rolls up the inclined plane!
Also two identical looking cylinders roll down at different rates.

b. Premature stopping of cylinder
A cylinder rolls half-way down an inclined plane and then stops.

c. Reversing cylinder
A cylinder rolls down the inclined plane, and then rolls back up!

d. Unpredictable Pendulum
Pendulum swings irregularly around, deflected by a hidden magnet.