This old film, a staple of most elementary physics courses, has left an indelible impression on countless students over the years. The bridge's roadway undulates gently at first, then abruptly starts heaving and twisting violently until it finally breaks apart.
Many students also remember the standard explanation for the disaster.
Physics textbooks and instructors usually attribute the bridge's collapse to the phenomenon of resonance. Like a mass hanging from a spring, a suspension bridge oscillates at a natural frequency. In the case of the Tacoma Narrows bridge, so the explanation goes, the wind blowing past the bridge generated a train of vortexes that produced a fluctuating force in tune with the bridge's natural frequency, steadily increasing the amplitude of its oscillations until the bridge finally failed. That explanation, however, is incomplete and flawed. One issue is the source of the periodic impulses that would produce resonance.