Vortex shedding is caused when air flows past a blunt structure. The airflow past the object creates alternating low-pressure vortexes on the downwind side of the object. The object will tend to move toward the low-pressure zone.

Eventually, if the frequency of vortex shedding matches the resonant frequency of the structure, the structure will begin to resonate and the structure's movement can become self-sustaining.

Some engineers believe that vortex shedding was one of the causes of the failure of the Tacoma Narrows Bridge in 1940.

References

• Failure of the Tacoma Narrows Bridge
• Another explanation of vortex shedding (includes a helpful diagram)
• A movie of the Tacoma Narrows Bridge failure