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Question
Explain free and forced vibrations. Give an experimental arrangement to illustrate the phenomenon of resonance.
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Solution
When a system or a body vibrates without receiving impulses from another system or body, its vibrations are said to be free vibrations. However, when a system or body vibrates on account of impulses received from another system or body, the vibrations are called forced vibrations. In such a case the body or the system vibrates with the frequency of the impulses received and not with its natural frequency.
Experiment Arrangement to illustrate Resonance: In the figure, the two pendulums have exactly equal lengths. However, the bob of the pendulum A is heavier. Displace the bob of the pendulum A by a little distance in a direction perpendicular to the plane containing the two pendulums. Then release the bob. The pendulum A will begin to oscillate. After a short while, you will find that the pendulum B also begins to vibrate. Note that the two pendulums have the same frequency. The pendulum A through the rubber tube applies impulses of the same frequency on the pendulum B Hence, the pendulum B begins to vibrate.
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