Resonance

Resonance is the special case of forced oscillation in which the frequency of the external periodic (driving) force exactly matches the natural frequency of the oscillator being driven. Because every push from the external force now arrives perfectly in step with the oscillator's own natural rhythm, energy is transferred into the system on every single cycle instead of partly cancelling out, so the amplitude of oscillation keeps building up, step after step, until it reaches a large -- potentially destructively large -- value. This dramatic amplitude build-up is called resonance, and the resulting large-amplitude vibrations are called resonant vibrations. A famous illustration is a glass shattering when a sound of exactly the glass's own natural (ringing) frequency is played loudly at it: the sound wave forces the glass to vibrate in resonance until the amplitude exceeds what the glass can withstand. The same principle, used constructively, lets a radio or television receiver 'tune i …