Question

Explain the following:

Why are the soldiers instructed to march out of step while crossing a bridge?

Answer 1

Reason for breaking the steps:

1. The bridge executes forced vibrations of frequency equal to the frequency of their steps when Each soldier exerts a periodic force in the same phase
2. The vibration produced in a body is in the same phase compared to the external periodic force
3. Now the natural frequency of the bridge happens to be equal to the frequency of the steps, the bridge will vibrate with a large amplitude due to resonance and the bridge may collapse.
4. So, the soldiers are advised to break their steps while crossing the bridge