Question

In Fig. A, B, C and D are four pendulums suspended from the same elastic string XY. The lengths of pendulum A and D are equal, while the length of pendulum B is shorter and of the pendulum C is longer. Pendulum A is set into vibrations.

1. What is your observation about the vibrations of pendulum D?
2. Give reason for your observation in part (a).
3. What type of vibrations take place in pendulums Band C?
4. Give reason for the answer in part (c).

Answer 1

1. The lengths of A and D are equal. When A and D's inherent frequencies are equivalent, D enters a resonance condition. In perfect phase with pendulum A, pendulum D swings at a rate of A.

2. This is because the lengths of A and D are equal.
3. Forced vibrations have taken hold of B and C.

4. Since the elastic string XY transfers the vibrations from pendulum A to pendulums B and C, the amplitude of their vibrations is similarly tiny.