PROPOGATION OF SOUND: Whenever a body is vibrating it produce a disturbance in the surrounding air. This disturbance reaches our ear in the form of waves thus producing the sensation of sound. When sound is produces, it reaches the listener through medium. Without any medium sound does not reach our ear. The most important medium of sound is air. When a tuning fork is struck against a rubber pad its prongs begin to vibrate and thus produce a sound we now discuss how sound waves are produced by a tuning fork, for this consider the motion of right prong of the vibrating tuning fork. It oscillating between two extreme positions “B” and “c”, when it moves form point “B” to “C” it compress the layer of air in front of it, this compressed layer moves forward and compress the next layer of air and so on when prong returns and moves from c to B , the pressure of adjacent layer of air decreases. Due to this decrease in pressure the air expands thus producing rarefaction. This process will continue. When sound waves reach the ear strike to eardrum then produce sensation of hearing. Thus above experiment prove that sound propagate in medium in the form of longitudinal waves.