Propagation of Sound
We know that sound is produced by vibration and it requires a medium for propagation. The medium is required for the sound to travel from one place to another. It is quite interesting to understand what happens to the particles of the medium.
When an object that is the source of the sound vibrates, it sets the particles of the medium into vibration. In the process, the nearest particles to the source get displaced from their mean or equilibrium position.
They in turn start to collide with the particles adjacent to them. The adjacent particles then also get displaced from their mean positions. They in turn do the same to their neighboring particles. This process continues in the medium till the sound reaches our ear.
Propagation of Sound
This is the way that sound travels through the medium. We see that particles of the medium are not traveling from the source to the human ear. It is the disturbance produced by a source that is traveling in the medium. The particles are merely oscillating from their mean positions.
This disturbance created by the vibrating object in the medium is what we call a sound wave.
Example: Propagation of Sound
Let us understand the propagation of sound with the help of a tuning fork. Here air is our medium of propagation.
Figure a shows the initial condition of the air particles of the medium when the tuning fork is in its original position, that is when the tuning fork is not vibrating.
Propagation of Sound: Tuning Fork
When we strike its prong on a rubber pad, we start hearing a sound. The two prongs of the tuning fork are vibrating. Let us concentrate on the motion of one of the prongs first. Say the one on the right.
When it is away from its mean position, it pushes and compresses the air particles around it, as shown in figure b. This creates a high-pressure region also called compression. This compression travels in the medium as a disturbance. Here the density is high. That is the particles are very close to each other.
When the prong comes back to its mean position, the pressure on the right decreases and keeps on decreasing further as the prong continues its motion towards the left. This creates a low-pressure region also called rarefaction, as shown in fig c. We see that at this point, the compression in the form of disturbance has reached this region. This rarefaction also travels in the medium as a disturbance. Here the density of particles is less. That is the particles are far away from each other.
As it continues to vibrate, we get a series of these compressions and rarefactions. This continuous sequence of compressions and rarefactions is what we call sound waves. The sound waves travel in the form of compressions and rarefactions.
A sound wave is a mechanical wave because a mechanical wave is the one that requires some material medium to travel. And as we know, a sound wave also requires some medium to travel. Thus, it is a mechanical wave.