Question

In 1831, soldiers marched across the Broughton Bridge in England in "lock step"—that is, marching in time together. As they marched, the bridge began to bounce in time with their footsteps; the amplitude of this bouncing became larger and larger until the bridge suddenly collapsed. Explain why the lock step of the soldiers caused this collapse and why afterward soldiers were ordered to "break step," or march at their own individual rates, as they crossed bridges.

Answer 1

The lock step of soldiers caused the collapse of the Broughton Bridge in 1831 due to resonance, which is why soldiers are ordered to break step when crossing bridges to prevent synchronized forces from amplifying bridge oscillations.

Step-by-step explanation:

The collapse of the Broughton Bridge in 1831 was caused by the phenomenon known as resonance. When the soldiers marched across the bridge in lock step, they exerted a rhythmic force on the structure, matching the bridge's own natural frequency of vibration. This synchronization amplified the oscillations until the energy exceeded the bridge's structural limits, leading to its collapse.

Henceforth, soldiers were ordered to 'route step' or 'break step' while crossing bridges to prevent such synchronized forces and avoid potential resonance. A similar principle led to the collapse of the Tacoma Narrows Bridge in 1940 when it entered a state of resonant oscillation due to strong winds.