What is a resonant object?

Answer 1

Basically it is an object that can be excited to vibrate or rotate by applying a force with some periodic frequency. The resonant object has preferred frequencies, or modes, where it optimally couples to sinusoidal forces. Think of a swing. If you move your feet back and forth witht eh right frequency, you can get eh swing to move higher. But if you change the frequency, the swing begins to loose energy. The swing with you on it is a resonant object.