Resonance is a very common phenomenon which occurs in many types of physical systems.
A familiar example is pushing a child on a swing. You can make the swing go higher and higher with relatively little effort if you time your push just right. The system is said to be in resonance and the amplitude of the motion increases rapidly. Probably the most dramatic example of resonance caught on film is the Tacoma Narrows Bridge collapse in 1940 . This photograph shows the twisting motion of the center span of the Tacoma Narrows bridge just prior to failure in 1940.