Question

As the army approached the bridge into the city, the commander told them to break step. He did not want the soldiers to march in cadence. Why did the commander give this order? A) Their rhythmic marching might resonate through the bridge and start the bridge swaying. B) Rhythmic marching sends vibrations down into the water and sound travels fastest in water. C) Marching in cadence causes the vibrations to travel faster through the air and reach the town faster. D) Rhythmic sounds are amplified in comparison to non-rhythmic sounds; the towns people would hear them coming.

Answer 1

A) Their rhythmic marching might resonate through the bridge and start the bridge swaying. 

Answer 2

Their rhythmic marching might resonate through the bridge and start the bridge swaying. If the vibration caused by the marching is in sync with the natural vibration of the bridge, the resonant vibrations can cause the bridge to sway, buckle, and even break apart. That is one reason why bridges have plates in them; to change the frequency of the resonant vibration.