# Wave

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.

Example

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.