Question

Distinguish between 

(1) free vibrations and resonance 

(2) forced vibrations and resonance (Two points of distinction).

Answer 1

(1) Free vibrations and resonance:

Free vibrations	Resonance
1. These are produced when a body is distributed from its equilibrium position and released.	1. It is produced by forced vibrations when the external periodic force has the frequency equal to the natural frequency (or nearly so) of the body.
2. The energy of the body remains constant in the absence of dissipative forces.	2. Energy is supplied continuously by the external periodic force to compensate the loss of energy due to the dissi‐ pative forces.

(2) Forced vibrations and resonance :

Forced vibrations	Resonance
1. These are produced by an external periodic force of any frequency	1. It is produced by an external periodic force whose frequency is equal to the natural frequency (or nearly so) of the body.
2. The frequency of vibrations is, in general, different from the natural frequency of the body	2. The frequency of vibrations is the same (or nearly so) as the natural frequency of the body.
3. The amplitude of vibrations is usually very small.	3. The amplitude of vibrations is large.
4. Vibrations stop as soon as the external force is removed.	4. Vibrations continue for rela‐ tively longer time after the external force is removed.