Experiment of the Month

Bowling Ball Demonstration Pendulum

The Physics Club has begun a program of demonstrations for schools with the construction of a portable bowling ball pendulum. Physics major C. Harmon, and Rob Schwartz designed the black frame for the pendulum so that it will fold and fit into the back of a car. The do-not-try-this-at-home sequence is shown below. (The pictures were taken in the physics club headquarters / study room.)

Begin Release

Swing Relax

eek!  Eek!

This is the physics major equivalent of walking on hot coals. Theory says that energy is conserved for the pendulum: i.e. that the energy is the sum of kinetic (1/2 m v 2) energy and gravitational potential (mgh) energy is constant. When the pendulum swings back to Mr. Harmon's face, it has also risen to the same height at which it was released.

If energy is conserved all the energy is now potential energy and the kinetic energy is zero. The velocity therefore is zero and the ball is not about to travel the extra centimeter and break anyone's glasses.

This analysis fails catestrophically if you give the ball a push when you release it.

To arrange for a demonstration, call the physics club advisor, Dr. Hendrick, at 717-872-3412