Any vibrating object has a natural frequency, which depends on factors such as the elasticity and shape of the object. Whenever an object or a system is set in oscillation at its natural frequency, as a result impulses received from some other system vibrating with the same frequency, resonance is said to have occurred. Resonance can occur in different kinds of systems: acoustical, mechanical, electrical and optical. Resonance results in increasing amplitude of vibration.
The amplitude of a child's swing can be increased by giving it small pushes in rhythm with the frequency of the swing. This is an example of resonance.
A diver jumping repeatedly on the edge of a diving board sets it into resonant vibration and thus gains considerable uplift before diving.
Sometimes the amplitudes that result from resonance can be disastrous. While crossing a suspended bridge soldiers are ordered to break step as otherwise the resonant vibrations caused by their marching can severely damage the bridge.
