Question

Explain why transverse mechanical waves cannot be propagated in liquids and gases?

Answer 1

Hint: The main characteristic that determines the propagation of a wave in any medium is the elasticity. Elasticity is defined as the property of a body to return to its original state when it undergoes deformation.

Complete step by step solution:
The wave is defined as the propagation of disturbance through the vibration of particles of a medium.

There are two types of transmission of the disturbance leading to two types of waves: Longitudinal and Transverse waves.

In longitudinal waves, the disturbance travels along the direction of vibration of the particles and in transverse waves, the particles vibrate at right angles to the direction of the travel of the disturbance.

The longitudinal waves are also called pressure waves, travel by applying momentary compressive force to the particles and it is released leading to rarefaction of the column. This disturbance propagates along the direction of wave propagation. This mainly happens in the gases.

However, this is not the case in transverse waves. In transverse waves, the particles move in highs and lows called crests and troughs respectively. Hence, there is considerable change in the shape of the medium. When there is a force that deforms the medium is applied, an equal and opposite force called restoring force acts in the opposite direction.

The property responsible for this is elasticity which represents the ability to restore the deformation when the deforming force is removed.

The concept of elasticity is more prominent in solids compared to the fluids. Hence, transverse waves are more common in solids and they do not travel in liquids and gases, which are fluids.

Note: In solids, the elasticity is represented by a constant number called Young’s modulus which represents the stiffness of the body or the resistance of the body to deformation. The equivalent quantity in fluids is called Bulk's Modulus, which represents the resistance in the pressure applied on the fluid column. Thus, the propagation of waves in fluids depends on the Bulk’s modulus.