Coupled Pendula Resonance

PIRA 3A70.33

A coupled pendula set can be made from heavy string, with the pendulum strings tied to a horizontal string held tightly between to supports.  The string for the pendula set shown at left is stored in a plastic zip-lock baggie with the weights.  Only two of the pendulum strings are the same length, and all have 20 g weights taped to their ends.

With the other pendula still, give one of the identical pendula a swing.  Ask the students which of the pendula will have the largest amplitudes after a few oscillations.

This is a good demonstration of resonance.