Footbridge resonance

HOW

1. Walk across the footbridge several times, taking steps in a different rhythm each time. What do you observe?
2. Stand in the middle of the footbridge and lightly jump rhythmically, varying the frequency of the jumps from time to time. What do you observe?
3. Stand in a pair in the middle of the footbridge and lightly jump rhythmically, varying the frequency of the jumps from time to time. Try to make the jumps simultaneous. What is happening?
4. Repeat the same as before, except that your jumps are out of sync. What do you observe now?

WHY

Jumping on the footbridge induces it to vibrate. If the frequency of the jumps matches the natural frequency of the footbridge, the swings are significant. As a result, you jump relatively high. The
frequency of jumps that gives the greatest swings of the footbridge is the resonance frequency.

If there is more than one person on the footbridge, the swings of the footbridge depend on each of the jumpers. If the jumps occur in an even rhythm, and in accordance with the natural vibration frequency of the footbridge, the swings will be the greatest and you will jump the highest.