State what resonance means.
A small ball is kept steady by a stretched string. One end of the string is attached to a wall and the other end is connected to a vibration generator, as shown in Fig. 4.1. At first, the vibration generator is off. A student pulls the ball vertically away from its rest position and lets it go. Fig. 4.2 shows how the ball's displacement varies with time after release.
State the phenomenon represented by the fall in the amplitude of the oscillations in Fig. 4.2.
Explain why the amplitude of the ball's oscillations decreases with time.
Determine the frequency of the ball's oscillations.
The vibration generator in (b) is switched on and its vibration frequency $f$ is increased gradually from $0$ to $10\ \text{Hz}$. On Fig. 4.3, sketch how the amplitude of the ball's oscillations changes with $f$.