 We have a giant bridge made out of concrete and steel, a suspension bridge, the Tacoma Narrows Bridge. Cars and trucks and buses are going over it every day. And unfortunately, where they built this bridge, there was a steady wind blowing across it. And one day, this wind induces a small vibration in the bridge, hardly noticeable. But the frequency of the vibration matches the resonant frequency of some part of the bridge, and the vibration gets larger and larger and larger until the bridge collapses into the river below.