Wave motion

Introduction 

The transfer of energy and momentum from one point of the channel to another without transporting the matter between those two points is defined as wave motion. There is a diverse classification of wave motion based on the energy channel of propagation, dimensions of the energy propagation by a wave, and energy transfer. Now, we will look at the classification and characteristics of wave motion.

Classification of wave motion

1. Mechanical wave motion
2. Transverse waves motion
3. Longitudinal wave motion
4. Standing waves or stationary waves
5. Progressive wave
6. Non-mechanical wave motion

Mechanical Waves (Elastic waves)

Waves that need a channel to start their propagation are elastic or mechanical. Here, the particles of the medium conduct periodic motion. The motion must be about the mean position when the wave propagates through the channel. 

Example: Propagation of waves over a string

The mechanical wave motion occurs when a disturbance occurs at any single point in a channel/medium. Here, the particle that went through the disturbance interacts with its nearby particle and transfers its energy to the following particle. Due to the elasticity of the medium, all the particles in disturbance tend to get back to the position of equilibrium. 

Properties of channel/medium for the propagation of the mechanical wave – 

1. The channel must contain inertia allowing the particles to store K.E.
2. It should contain elasticity.
3. There should be a minimum force of friction among the medium’s particles

Transverse wave motion

In transverse wave motion, the medium’s particles tend to vibrate in the perpendicular direction to the propagation direction of the wave. The area of the highest upward displacement is known as crest, and the area of the lowest downward displacement is known as a trough. The introduction of transverse waves takes place through a channel that maintains a shape conservation and rigidity modulus. The best example of this is string waves.  

Longitudinal wave motion

A longitudinal wave needs a medium that contains a bulk modulus of volume elasticity to conduct its propagation. Here, the waves move through a channel in the form of rarefaction and compression. The medium particles vibrate at their equilibrium position in the wave’s propagation direction. 

The area of higher pressure is known as compression, and the area of lower pressure is known as rarefaction. The best example of this is the waves of sound in a tube.

Standing waves

Standing waves are formed by two waves moving in opposite directions. These waves oscillate in time but their peak amplitude does not move in space. These waves are confined to a single area. There is no transfer of momentum and energy here. 

Progressive waves

Here, the waves tend to transfer momentum and energy between all the medium particles.

Non-mechanical waves

When the introduction of waves does not need a medium to conduct propagation, then the wave motion is known as non-mechanical waves. Even a vacuum is suitable for these waves to start propagation. Non-mechanical waves are transverse. 

Example: Matter and electromagnetic wave

Characteristics of wave motion

1. The disturbance in the particle travels with the help of the medium. It happens due to the repetition of particle’s  periodic oscillations. The oscillation of a particle occurs about the equilibrium or mean position. 
2. There is a transportation of momentum and energy between two points without transporting the particles of the medium. 
3. There is a consistent difference in the phase among the medium’s particles as every particle comes in contact with disturbance a little later than its preceding particle.
4. The travelling velocity of the wave is different from the vibration velocity of the particles about the equilibrium or mean position.
5. For the medium, wave motion velocity stays constant, whereas the particle’s velocity shifts consistently due to its mean and equilibrium position vibration. 
6. The particle’s velocity reaches its maximum value at the mean position while getting zero at the extreme.
7. Standing wave is the only type of wave in which there is no tranfer of energy between adjacent particles and it appears like the wave is not moving forward.

Conclusion

Waves are an integral part of physics. Here, we covered all the essential definitions most commonly used in the chapter on wave motion. You need to focus more on learning mechanical motion and its classification.