Question

In Fig. 17, \(P, Q, R\) and \(S\) are four pendulums suspended from the same elastic string \(X X^{\prime}\). Lengths of pendulum \(P\) and \(S\) are equal, while the length of \(Q\) is smaller and \(R\) is longer. The pendulum \(P\) is set into vibration. What is your observation? Give reasons for your observation.

Answer 1

Observation:

When pendulum P is set into vibration, pendulum S starts vibrating with the maximum amplitude. Pendulums Q and R vibrate only slightly.

Reason:

Pendulums P and S have equal lengths, so they have the same natural frequency. Therefore, resonance occurs in pendulum S, producing large-amplitude vibrations. Q and R have different lengths and hence different natural frequencies, so they do not resonate strongly.