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.
Answer
A
absorption, because the bridge absorbed all the energy of the wind
B
diffraction, because the wind moved around the bridge, which set the bridge into motion
C
interference, because constructive interference occurred when the wind frequency matched the natural frequency of the bridge
D
interference, because destructive 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 associated with constructive interference, in which repeated forces reinforce the motion rather than cancel it. Therefore, choice C, constructive interference, best describes the result; destructive interference would reduce the movement.
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