Longitudinal Waves Compression

Introduction:      

When a stone is dropped into water in a pond. waves are produced at the point where the stone strikes and water. The waves (ripples) travel outward and particles of the water vibrate up and down about their mean positions. This can be clearly seen when the leaves floating on the surface of the pond move up and down as the ripples pass on. They do not travel along the wave. Similarly, when a tuning fork is set into vibrations, waves are produced in the surrounding air making the particles of the air oscillate about their mean positions. Hence a wave motion can be defined as a form of disturbance which travels through the medium due to repeated periodic motion of the particles of the medium about their mean positions, the disturbance being handed over from one particle to the next. in the process the energy and momentum of the particles is successively transmitted through the medium in the wave form known as a progressive wave or a travelling wave. Such a wave travels with a constant speed in the medium.

Longitudinal Waves Compression

The direction of propagation of waves relative to the direction of vibration of the particles of the medium classifies them into two types, namely  longitudinal waves and transverse waves.

Longitudinal waves :
 If the particles of the medium vibrate parallel to the direction of propagation of the waves, the waves are called 'Longitudinal waves'. The propagation of longitudinal waves can be demonstrated as shown in the figure below. 

Longitudinal Waves Compression : Simulation

Let a light spring held horizontally be given a push in the same direction. The spring gets compressed sending a pulse of pressure along the spring. Soon this compression tends to release the pressure in the region by pushing the neighbouring (particles) layers of the spring. This is known as rarefaction. Thus the compressions transmitted horizontally along the length of the spring .If the pushing at the end of the spring is repeated at regular intervals of time a periodic longitudinal progressive wave takes place along the length of the spring.
Sound waves are longitudinal waves. Longitudinal waves can travel in solids, liquids and in gases as well.