Question

A platoon of soldiers marches on a road in steps according to the sound of a Marching band. The band is stopped and the soldiers are ordered to break the steps while crossing a bridge. Why?

Answer 1

The march in step is a type of forced oscillation of the bridge. If the frequency of the steps be near to the frequency of the bridge the resonance may occur that will result in a very large amplitude of the bridge oscillation. It will be damaging to the bridge. Hence the march on the bridge is by breaking the steps.