In 1940, the Tacoma Narrows Bridge across the Puget Sound collapsed. The bridge was a suspension bridge. The wind blowing through the narrows matched the natural frequency of the bridge. This resulted in a large movement of roadway, which eventually caused the bridge to fail. What characteristic of waves caused the bridge to collapse?
Answer
A
diffraction, because the wind moved around the bridge, which set the bridge into motion
B
absorption, because the bridge absorbed all the energy of the wind
C
interference, because destructive interference occurred when the wind frequency matched the natural frequency of the bridge
D
interference, because constructive interference occurred when the wind frequency matched the natural frequency of the bridge
Explanation
When the wind’s frequency matched the bridge’s natural frequency, the bridge resonated and its vibrations grew larger. This is like constructive interference: repeated pushes added energy to the motion instead of canceling it out. Therefore, the correct choice is interference through constructive interference, not diffraction or absorption.
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