Question

P is a particle in the path of sound waves progressing in the OX direction. What is the direction of vibration of the particle P?

Answer 1

Hint: The sound waves travel like longitudinal waves. When they pass the particle P then the particle moves along the direction in which these sound waves vibrate. The longitudinal waves vibrate along the direction of propagation of the wave.

Complete answer:
We are given a tuning fork which produces sound waves when disturbed from its equilibrium position. A particle P is kept in the path of these sound waves and is free to move due to the wave incident on it. We need to find out the direction in which the particle moves.
In order to answer this question, we must know the nature of the sound waves. The sound waves are actually longitudinal waves. They need a medium for travelling as they travel like a disturbance through the particles of a medium. They consist of compressions and rarefactions travelling in the direction of propagation of the waves. It can be visualized through the following diagram.

The regions of the higher density occur due to the compression where particles move close to each other while regions of lower density occur due to rarefaction where particles move away from each other.
The result of compression and rarefaction is that the particles of the medium move in the same direction as the direction of the propagation of sound waves. Since we are given that the sound waves are travelling along OX direction then particle P will also move along OX direction.

Note:
It should be noted that in longitudinal waves, there are density fluctuations taking place in the medium as the longitudinal wave travels through the medium. When we talk about the transverse waves, the particles vibrate in direction perpendicular to the direction of the propagation of the wave.