What is forced vibrations?

Forced vibrations are vibrations that occur when a body is made to vibrate by an external periodic force. If you keep applying an outside push or force to an object again and again at regular intervals, the object starts vibrating. These are not natural vibrations but happen due to the continuous external force. These are called forced vibrations.

For example, if you strike a tuning fork and bring it near another tuning fork of the same frequency, the second fork also starts vibrating. But if you now tap the first fork continuously or use a machine to keep it vibrating at regular time intervals, you are forcing the second fork to vibrate too. This is an example of forced vibrations.

Another example is when a loudspeaker produces sound. The electric current flows in and out, forcing the diaphragm to vibrate at the frequency of the electric signal. The air around it is forced to vibrate, and this produces sound waves that we hear.

Forced vibrations are very useful in musical instruments, loudspeakers, and even buildings, where sometimes they have to be prevented during earthquakes.