Longitudinal Wave

Dhristi JEE 2022-24

Introduction to Longitudinal Wave

A wave that consists of a vibration or any periodic disturbance which happens in the same direction like the advance of the wave. When you compress one end of the coiled spring and release it, it experiences a wave of compression which travels to the length of it, stretching follows it. The coil of the spring has a point that moves with the wave and returns from the same path, while returning it passes from the neutral position and then again reverses its motion. Moving of the sound through air results in compressing the gas in the direction where sound waves are travelling while they vibrate back and forth. The seismic waves which are primary p, are also longitudinal. 


All the particles in the longitudinal wave, vibrates to its rest position which is normal and with the axis of propagation, and all the particles that participate in the wave motion behaves in the same way, except in phase of vibration, there is a case of progressive change that means every particle finishes its cycle of reaction at a time that is later. With the combined motions, it results in moving forward in the alternating region of compression and rarefaction towards the propagation’s direction. 


The pattern of disturbances is of two types or in other words the formation of waves is done in two different methods. We know that the energy of the particles in motion is transmitted in the form of waves. Depending on the type of motion two forms of waves are classified, the first one is a longitudinal wave and the second is a Transverse wave. The longitudinal motion or the longitudinal wave are found when the energy has to be transmitted within the medium. Whereas the transverse waves are formed at the surface. 


Terms Used in Longitudinal Waves

  • Crest - a point on the medium which has the maximum amount of positive or upward displacement from the position of the rest, that is known as the crest of the wave. 

  • Trough - it is just the opposite of crest. The point on the medium which has the maximum amount of negative or downward displacement from the position of the rest, that is known as the trough of the wave. 

  • Amplitude - when the particle on the medium from the position of rest has a maximum amount of displacement, it is termed as the amplitude of the wave. The distance from the rest to the crest in a way is the amplitude. The amplitude can be calculated from the position of the rest to the position of the trough. It can also be calculated like the distance of the line segment which is perpendicular to the position of the rest and moves vertically upward from the position of the rest towards point A. 

  • Wavelength - the length of one full wave cycle is the wavelength of a wave. When a pattern is repeated, it is known as a wave. The pattern repeats itself in a regular and periodic way over space and time both. It can be calculated per the distance between crest to crest or can be calculated from trough to trough. 


Examples of Longitudinal Waves

The longitudinal waves are mechanical waves and these are readily used in nature for transmitting energy from one point to another within the medium. There are several examples of longitudinal waves. Sound waves are the most common example of longitudinal waves, pressure waves, spring waves, etc… Let’s have a look at these examples in detail to understand the concept of longitudinal waves.


The best example of longitudinal waves is the sound wave, in order to receive the sound wave we definitely require a medium which is generally an air medium. This is the main reason why the sound waves can not propagate in a vacuum. In this article, we will discuss what are longitudinal waves, examples of longitudinal waves, formation of longitudinal waves, etc…


1. Sound Waves in the Air:

Yes, the sound waves are longitudinal in nature. When we speak, the sound wave propagates through the air medium and reaches the audience. The sound waves are the best example of a longitudinal wave and are produced by vibrating or disturbing the motion of the particles that travel through a conductive medium. An example of sound waves in a longitudinal direction of propagation is the tuning fork. In sound waves, the amplitude of the wave is always the difference between the maximum pressure caused by the wave and the pressure of the undisturbed air. The propagation speed of sound depends upon the type, composition of the medium, and temperature through which it will propagate.


2. The Primary Waves of an Earthquake:

It is said that animals can sense earthquake waves much before humans. They have the ability to sense the seismic P waves, which travel only in the interior of the earth. Even humans can experience a little bump and rattle of these waves, but they are mostly unnoticeable to us. The P waves are the fastest waves, and they require a medium to travel either solid or liquid. The P waves cause the interior of the earth i.e., tectonic plates to move back and forth (in other words to oscillate)  in a longitudinal manner, which leads to the surface waves i.e., seismic S waves, which we can feel.


3. The Vibration in a Spring:

Consider a small spring, suppose we knock the end of the spring, the waves that formed will flow through the spring. The waves formed will propagate within the spring and hence they are considered to be the longitudinal waves. At the same time, if one end of the spring is fixed, the waves will propagate in the up and down direction resulting in transverse waves.


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4. The Tsunami Waves:

We know that tsunamis are dangerous natural disasters that may lead to severe loss to human beings. Tsunamis cause damage to coastal regions (sea shore) and that’s the reason why people residing in coastal regions are afraid of them. Most people think that sea waves are transverse waves as they keep travelling in to and fro motion i.e., they go up and down continuously. However, water or sea waves, including Tsunami, are an example of both transverse as well as a longitudinal wave. When the waves reach the shore or remote areas, they become comparatively smaller and thinner, and water molecules move parallel to the wave, hence making it a longitudinal wave.


Transverse and Longitudinal Waves:

Let us understand what are transverse and longitudinal waves with the following list of differences. Both the longitudinal and transverse play an important role in elaborating the concept of sound. Thus the major difference between the transverse wave and longitudinal wave are as follows:

Sl. No

Longitudinal Waves

Transverse Waves

1.

longitudinal Wave Definition:

To define longitudinal waves, it is the type of disturbance, such that the particles executing the to and fro motion about their mean position will have longitudinal waves.

Transverse Wave Definition:  

The particles executing the up and down motion about their mean position will have transverse waves.

2.

The longitudinal waves consist of compression and rarefaction, hence they are also referred to as the compressional wave.

The transverse waves consist of crest and trough.

3.

Longitudinal waves can propagate through any medium, such as the longitudinal can propagate through a gas medium, air medium, water, solids, etc... 

Transverse waves can only propagate only through solids and at the surfaces of the liquid medium.

4.

The longitudinal waves are graphically represented by the density-distance graph.

The transverse waves are graphically represented by the displacement-distance graph.

5.

In longitudinal waves, the pressure and density will be during maximum for compression and minimum during rarefaction

In transverse waves, there is no variation in the value of density and pressure.

6.

Examples of longitudinal waves:

Sound waves, Vibration in spring, Tsunami waves, etc...

Examples of transverse waves:

Electromagnetic waves, water waves caused by external disturbance, etc...

7.

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Did You Know:

Dogs are sensitive to sound at a higher frequency than humans, allowing them to hear noises that humans can not.


Sound waves are used by many animals to detect danger, warning them of possible attacks before they happen.


Sound can not travel through a vacuum (an area empty of matter), it requires a medium.


The speed of sound is around 767 miles per hour.


The loud noise you create by cracking a whip occurs because the tip is moving with a high frequency and speed it breaks the speed of sound.

FAQs on Longitudinal Wave

1. What are Three Examples of Longitudinal Waves?

Examples of longitudinal waves: Sound waves, Vibration in spring, Tsunami waves, etc.

2. What are the Characteristics of Longitudinal Waves?

Characteristics of longitudinal waves, just like in the transverse waves the following properties can be defined for longitudinal waves: wavelength, amplitude, period, frequency and wave speed. The main characteristic difference is, instead of crests and troughs, longitudinal waves have compressions and rarefactions

3. What do you understand about wave velocity ? 

When the distance is travelled in a motion per unit time in a cyclic or periodic manner in any direction, it is known as Wave velocity. The common use of wave velocity is to the speed even though velocity relates to both speed and direction. The wave’s velocity equals the product of frequency and it’s wavelength, which is independent of its intensity. A solid that is rigid in nature, a point vibrates, longitudinal and transverse waves, both of the Similar frequency are sent out and because of the reason that longitudinal waves have wavelengths which are longer, it cannot move fast. To understand it better, look at the online study material provided by vedantu. 

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