Nature And Propagation Of Sounds – We have seen that all sounds are produced by vibrating bodies. During its vibratory motion, a vibrating body moves to and fro around its rest position and produces compression waves in the surrounding medium. These compression waves are called the sound waves which travel from one place to the other. We can get more information about the production and propagation of sound by considering in detail the motion of the vibrating tuning fork.
A particular sound is produced by striking a tuning fork on a rubber pad. The prongs of such a tuning fork begin to vibrate. A vibrating tuning fork is shown in Fig. 13.3 its right hand prong vibrating about its rest position O between two points A and is B. it compresses the layer of air in front of it.
The compressed layer transfers its increased pressure to the air layer nest to it and after doing so it comes to its normal state. This process continues and the compression produced by rightward movement of the prong, moves outwards. A moment later the right hand prong starts moving towards the position A.
During such a motion of the prong pressure in the adjacent air layer decreases and a rarefaction is produced here. The first layer, where a rarefaction has been produced, transfers its decrease in pressure to the next layer and after doing so it comes to its normal state. This process also continues and the rarefaction produced in the first layer moves outwards.
As the tuning fork continues to vibrate, compressions and rarefactions are produced and travel outwards one after the other. Such a series of compressions and rarefactions are the sound waves. As the molecules of air move in the direction of waves during their vibratory motion, we can conclude that sound waves are compressional waves.
We have seen that sound waves can travel through air. Sound waves can also travel through gases, liquids and solids. Now we perform some experiments which will show that a material medium is necessary for the sound waves to travel from the vibrating body to our ears.