The Transmission of sounds

During the process of transmission, it is obvious that something passes from the sounding body to the ear, in order to produce the sensation of sound from the motion of the sounding body we guess that some sort of wave motion passes outwards from it. It can be easily shown that a medium (air or some other medium) is indispensable for the propagation of sound.

All materials, however, can transmit sound waves, if a faint tapping or scratching be made at one end of a long table, on putting the ear to the other end of the table, this sound can be heard even when the sound is too faint to be heard if the ear is not placed close to the wood. This shows that sound waves have been transmitted through the wood.

If you examine it carefully, you will notice that every source of sound or part of it vibrates when it is set to produce sound. We hope you are familiar with the prongs of a tuning-fork. The prongs of a sounding tuning-fork and the plucked string of a guitar can actually be seen to vibrate. The vibration of a drum or a bell may not be visible but they can often be felt: when they are checked by the hand the sound ceases.

Question

What is vibration ?

A vibration is a rapid to and fro motion which is continually repeated.

The vibration of a prong of a tuning-fork may be investigated by attaching a bristle to one of its prongs, and drawing under it a smoke glass plate while the prongs are vibrating. (Image 1.1.1)

(Image 1.1.1)

If a glass plate is moved with a uniform velocity the trace made by the  bristle will be similar to the wave pattern shown in Image 1.1.2

(Image 1.1.2)

This particular type of vibration is the simplest possible, and is called simple harmonic motion as you know from earlier sessions.

Due to this vibration of the source of sound, the surrounding medium gets disturbed and this disturbance travel through the medium without the medium moving bodily with it . We call this is a wave. a wave allows energy to be transferred from one point to another some distance away without any particles of the medium travelling between the two points. 

There are many kinds of waves such as light waves, radio waves, water waves and wave in stretching strings, rods and so on. All these waves can be divided into two main categories. 

1. Transverse waves
2.  Longitudinal waves