Question

The above picture shows a mother pushing her daughter sitting on a swing. The swing is going through the positions A, B, C where A and C are extreme positions and B is the mean position.

1. Which is the right position i.e. at A, B or C, for the mother to give a constant periodic push to the swing every time in the forward direction to increase the amplitude of the swing?  (1)
2. Name the phenomenon involved in this.  (1)
3. Explain with this example how this phenomenon helps to increase the amplitude of the swing.  (2)

The above picture shows a mother pushing her daughter sitting on a swing. The swing is going through the positions A, B, C where A and C are extreme positions and B is the mean position.

1. Which is the right position i.e. at A, B or C, for the mother to give a constant periodic push to the swing, every time in the forward direction, to increase the amplitude of the swing?  (1)
2. Name the phenomenon involved in this.  (1)
3. On the basis of this example, explain how this phenomenon helps to increase the amplitude of the swing.  (2)

Answer 1

1. A is the correct position for the mother to give a constant periodic push to the swing each time it moves in the forward direction, in order to increase the amplitude of the swing.
2. The phenomenon involved is resonance.
3. When the mother gives pushes periodically at regular intervals such that the frequency of the applied force matches the natural frequency of the swing, resonance occurs. Since the push is given in the same direction as the swing’s motion each time, the energy supplied adds up cycle after cycle, increasing the total energy of oscillation, and hence the amplitude of the swing increases gradually.