The waves which transfer energy by moving away from the source of disturbance are called progressive or traveling waves. Example Consider two persons holding the opposite ends of the Suddenly one person gives a jerk to the rope. The disturbance in the rope produces a pulse which moves toward Another person. When this reaches the other person, it pushes his hand upward.
SO the energy and momentum transfer. From one person towards the other person. This is an example of a progressive wave. The jerking of hand its source and rope is the medium for the propagation of the waves. Kinds of waves There are two kinds of progressive waves
The waves, in which particles Of the medium are displaced perpendicular to the direction of propagation Of waves are called as transverse ‘waves. Take a loose spring coil (slinky spring) for illustration of motion of source in generating waves in a medium. Slinky is these/I spring H%ieh hos small initial length but a relatively large extended figure. Consider’ a horizontal spring system with its one end fixed.
When the free end is moved from side to side, a pulse of a wave having a displacement pattern as shown in the figure will run along the spring. This indicates that the displacement of particles is perpendicular to the direction of propagation of the wave, hence transverse waves are produced.
Longitudinal Waves (Compressional waves) The waves, in which particles of the medium are displaced’ along the direction of propagation of the waves, are called as longitudinal wavés. If of the spring is moved back and forth, along the path Of the spring.
Then the waves are produced in which displacement of the spring is along to the direction of propagation Of wave, and such waves are called longitudinal waves, as shown in the figure.
Note (Why sound waves in air are longitudinal?) Both types of waves can be up in solids. In fluids, however, transverse waves die out very quickly and usually cannot be produced at all. That is why; sound waves in air are Longitudinal.