When a vibrating body is maintained in the state of vibration by a periodic force of frequency (n) other than its natural frequency of the body, the vibrations are called forced vibrations. The external force is driver and body are driven. The body is forced to vibrate with an external periodic force. The amplitude of forced vibration is determined by the difference between the frequencies of the driver and the driven. The larger the frequency difference, smaller will be the amplitude of the forced oscillations.
Examples: (i) Soundboards of stringed instruments execute forced vibration,
(ii) Press the stem of the vibrating tuning fork, against tabla. The tabla suffers forced vibration.