RESONANCE

The tendency of an object to absorb more energy when the frequency of the oscillations matches the object’s natural frequency of vibration therefore causing its
amplitude to grow larger and larger rapidly

Natural frequency:
The frequency that an object tends to oscillate at when disturbed by an external force.

Forced Oscillation:
An oscillation caused by external force acting on the system.

Resonance:
Can be observed using a Barton’s Pendulum.The Driving Pendulum forces six pendulums
of different lengths to vibrate.

Resonance: A phenomenon
that happens when a vibration system is forced to vibrate with its natural frequency.

Example: 
If an Opera sings at the same frequency as the natural frequency of a glass, the glass tends
to absorb more and more energy and eventually will break.