Transverse & Longitudinal Waves: Definition, Examples & Differences

Transverse and longitudinal waves are different types of mechanical waves. It is important to understand what are waves to understand different types of waves. A wave can be defined as a dynamic disturbance travelling from one point of medium to another, it is further associated with one or more medium properties. Waves based on their propagation, production, dimension etc., can be classified into various categories like matter waves, standing waves, progressive waves, gravitational, mechanical, one dimensional, two dimensional etc. Out of all these, the most familiar waves, such as waves on a string, water waves, sound waves, seismic waves, etc., are referred to as mechanical waves.

Embibe offers a range of study materials for students of the CBSE board. These study materials include NCERT books, previous year question papers and solution sets. A team of experts work effectively towards preparing these solution sets. Students can follow these solution sets to understand the correct approach to answer the questions correctly.

Mechanical Wave: Definition

A mechanical wave is the type of wave that involves the oscillation of the matter, and therefore, it transfers energy from one point to the other in a medium. A mechanical wave is generated when the matter is disturbed, and a source of energy is required to initiate a mechanical wave. A mechanical wave needs a medium to propagate, i.e. these waves can not travel through the vacuum. These waves travel through a material medium that can be solid, liquid or gas at a wave speed determined by that medium’s elastic and inertial properties. While waves, in general, can travel over long distances, the distance that a mechanical wave can cover is limited by the transmission properties of the medium.

The particles of the medium vibrate at their places as a mechanical wave passes through the medium, and they transfer the energy of the disturbance to their neighbouring particles and so on. The particles of the medium do not move with the wave; only energy propagates from one particle to the next. The direction of propagation of energy through the medium is along the direction of propagation of the wave.
Based on the motion of the particles, the mechanical waves can be classified into the following two categories:
1. Transverse Waves
2. Longitudinal waves

Transverse wave

The type of mechanical wave in which the oscillation of the constituents of the medium is perpendicular to the direction of propagation of the wave, such a wave is called a transverse wave. In these waves, particles are displaced at right angles to the wave direction.
To visualise how a transverse wave travels through a medium, consider the following scenario:

1. Take a long rope and stick it to a wall. Hold the rope at its end and stretch the rope such that it is taut. Now carefully give a single jerk (up and down movement) to the rope. You will see that a small pulse is created in the rope that travels away from you.
   
2. As the wave moves along the rope, each constituent atom of the rope shifts up and down from its mean position generating a series of crests and troughs.
3. You will observe that all rope points get displaced momentarily as this pulse or disturbance travels through them, but as soon as the disturbance moves away, they come to rest.
4. If the rope is very long compared to the size of the pulse, the pulse will die out before reaching the wall. But if the length of rope and size of the pulse is appropriate enough, we will be able to see the pulse getting reflected after it strikes the wall.
5. Now instead of a single jerk, if you shake the rope sinusoidally up and down continuously, you will find that a periodic sinusoidal disturbance is created on the rope, and the elements of the rope oscillate about their equilibrium mean position as the pulse or wave passes through them.
6.  These oscillations are normal to the direction of motion of the wave along the rope.  This is an example of a transverse wave.

So far, we have learnt that the constituents of the medium in a transverse wave vibrate normally along the path of the wave’s motion. This means that each constituent of the medium will be subject to shearing stress.
Shear stress is defined as stress in an elastic solid caused by a shear force that tends to deform them by making different sections or layers of the solid move in different directions.
Solids and strings have substantial shear modulus. Therefore, they can sustain shearing stress. But fluids do not have a fixed shape and hence no shear modulus, i.e. they yield under shearing stress. Thus, the transverse wave can travel through solids and strings under tension, but these waves are not possible in fluids.

Terms Related to the Propagation of Transverse Waves

1. Crest: Crest is the point on a wave, where the value of upward displacement is maximum, i.e. the highest point on a wave.
2. Trough: Trough is a point on a wave, where the value of downward displacement is maximum, i.e. the lowest point on a wave.

Examples of Transverse Waves

1. The ripples observed on the surface of the water.
2. The vibrations produced on a guitar string when it is plucked.
3. Group of people performing a Mexican wave in a sports stadium.
4. The seismic secondary waves or \(S-\)waves during an earthquake.
5. Light waves, radio waves and other electromagnetic waves.

Longitudinal wave

The type of mechanical wave in which the oscillation of constituent elements of the medium is along the direction of propagation of the wave, such a wave is called a Longitudinal wave. In these waves, the medium particles are displaced parallel to the wave moving through the medium.
To visualise how a longitudinal wave travels through a medium, consider the following scenario:

1. We have all been vaccinated to prevent us from getting affected by a disease. The vaccine dose is put in our body by a syringe. The motion of the piston in a syringe can produce longitudinal waves.
2. Take a long syringe, i.e. a long pipe with a piston at one end. Now push the piston of the syringe up and slowly pull the syringe down such that the injection tube is now filled with air.
3. Give a single push forward and a simultaneous pull back to the piston. You will find with the push, a high-density region and with pull, a low-density region is created.
4. This pulse so created travels along the length of the injection tube containing compression followed by rarefaction.
   
5. Suppose this push and pull of the piston is sinusoidal and continuous. In that case, a sinusoidal wave is generated in the air around the injection, which travels along the length of the injection tube.
6. The oscillations of the elements of air in the syringe are along the direction of wave motion. Thus a longitudinal wave is created.

The propagation of a longitudinal wave through a medium leads to the build-up of compressive stress across the medium. Compressive stress is possible in both solids and fluids. Thus, a longitudinal wave can propagate through the air and as well as through a wooden desk.
Now, if a metal bar possesses both bulk and elastic moduli, both transverse and longitudinal waves will be able to propagate through it. Although the speed of these waves at which they travel through the metal bar may vary.

Terms Related to the Propagation of Longitudinal Waves

1. Compression: Compressions are the region of high pressure formed when particles of the medium are very close.
2. Rarefaction: Rarefactions are the region of low pressure formed when particles of the medium are far apart.

Longitudinal Waves: Examples

1. The sound waves produced as we talk.
2. The ultrasound waves.
3. The seismic pressure waves or \(P-\)waves associated with Earthquakes.
   

Transverse vs Longitudinal

Transverse wave	Longitudinal Wave
The constituent elements of the medium vibrate perpendicular to the direction of motion of the wave.	The constituent elements of the medium vibrate along the direction of motion of the wave.
These waves propagate in the form of crests and troughs.	These waves propagate in the form of compressions and rarefactions.
These waves generate shear stress in the medium.	These waves generate bulk stress in the medium.
These can be produced in solids and liquid surfaces.	These can be produced in solids, liquids and gases.
The seismic \(S\) waves are an example of transverse waves.	The seismic \(P\) waves are an example of longitudinal waves.
These create a disturbance in two dimensions.	These create a disturbance in one dimension only.
Transverse waves can be aligned or polarised.	Longitudinal waves can not be aligned or polarised.
At a cricket match, when the people execute a wave by moving up and down their position as the wave travels through could be considered a transverse wave.	Now, if instead of standing up, if people were to bump their shoulder into their neighbour, along the direction of the wave, this would be a longitudinal wave.

Surface Wave

It is a mechanical wave in which the disturbance travels along with the interface between two different media. In a surface wave, the motion of the constituent elements of the medium is both back and forth and up and down about their mean position. This means that particles oscillate both along and perpendicular to the direction of wave motion. Thus, a surface wave is a combination of both transverse and longitudinal waves.
The Seismic waves generated between the boundary of air and rocks during an earthquake are examples of surface waves.

Summary

A mechanical wave is the type of wave that involves the oscillation of the matter, and therefore, it transfers energy from one point to the other in a medium. A mechanical wave is generated when the matter is disturbed, and a source of energy is required to initiate a mechanical wave.
The mechanical waves can be classified into the following two categories:

1. Transverse Waves: The type of mechanical wave in which the oscillation of the constituents of the medium is perpendicular to the direction of propagation of the wave; such a wave is called a transverse wave. Transverse waves can be seen in the ripples observed on the surface of the water or the vibrations produced on a guitar string when it is plucked.
2. Longitudinal waves: The type of mechanical wave in which the oscillation of constituent elements of the medium is along the direction of propagation of the wave; such a wave is called a Longitudinal wave. Sound waves and ultrasound waves are examples of longitudinal waves.

Frequently Asked Questions (FAQs) on Transverse and Longitudinal Waves

Frequently asked questions related to transverse and longitudinal waves are listed as follows:

Q. What is a mechanical wave?
Ans: A mechanical wave is the type of wave that involves the oscillation of the matter, and therefore, it transfers energy from one point to the other in a medium.

Q. What is a longitudinal wave?
Ans: A type of mechanical wave in which the constituent elements oscillate along the direction of the wave motion is known as longitudinal wave—for example, sound waves.

Q. Particles of a medium are moving at \(90^\circ \) to the direction of motion of wave; what type of wave is this?
Ans: The wave in which particles of the medium vibrate perpendicular to the direction of motion of the wave is a Transverse wave.

Q. Give a few examples of a transverse wave.
Ans: 1. The vibrations are produced on a guitar string when it is plucked.
2. Group of people performing a Mexican wave in a sports stadium.

Q. Can a wave be both transverse and longitudinal?
Ans: Yes, Surface waves are a combination of transverse and longitudinal waves.

Q. Can mechanical waves travel through the vacuum?
Ans: No, mechanical waves can only propagate through a  material medium.

Study The Concept Of Longitudinal Wave

We hope this detailed article on Transverse and Longitudinal Waves helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.