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A wave is a disturbance which propagates energy and momentum from one place to the other without the transportation of matter.

Necessary properties of the medium for wave propagation

  • Elasticity: So that particles can return to their mean position, after having been disturbed.
  • Inertia: So that particles can store energy and overshoot their mean position.
  • Minimum friction amongst the particles of the medium.
  • Uniform density of the medium.

Characteristics of wave motion

  • It is a sort of disturbance which travels through a medium.
  • Material medium is essential for the propagation of mechanical waves.
  • When a wave motion passes through a medium, particles of the medium only vibrate simple harmonically about their mean position. They do leave their position and move with the disturbance.
  • There is a continuous phase difference amongst successive particles of the medium, i.e., particle 2 starts vibrating slightly later than particle 1 and so on.
  • The velocity of the particle during their vibration is different at different positions.
  • The velocity of wave motion through a particular medium is constant. It depends only on the nature of medium not on the frequency, wavelength, or intensity.
  • Energy is propagated along with the wave motion without any net transport of the medium.

Mechanical waves

The waves which require medium for their propagation are called mechanical waves.

Waves on string and spring, waves on water surface, sound waves, seismic waves.


Non-mechanical waves

The waves which do not require medium for their propagation are called non-mechanical or electromagnetic waves.

Transverse waves

Particles of the medium execute simple harmonic motion about their mean position in a direction perpendicular to the direction of propagation of wave motion.
  • Transverse waves travel in the form of crests and troughs.
  • A trough is a portion of the medium which is depressed temporarily below the normal position of the rest of the particles of the medium, when a transverse wave passes through it.
  • Examples of transverse wave motion: Movement of string of a sitar or violin, movement of the membrane of a tabla or dholak, movement of kink on a rope, waves set-up on the surface of water.
  • Transverse waves can be transmitted through solids. They can be setup on the surface of liquids. But they cannot be transmitted into liquids or gases.

Longitudinal waves

If the particles of a medium vibrate in the direction of wave motion the wave is called longitudinal.
  • Longitudinal waves travel in the form of compression and rarefaction.
  • These waves can be transmitted through solids, liquids, and gases because for the propagation of these waves, volume elasticity is necessary.

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