Sound is a part of our sensory experience. We perceive sound through our ears. Sound is a form of energy. It is a vibration which propagates through a medium.Sound travels in the form of a wave. A sound is produced due to the to and fro motion of the particles of the medium when the sound wave passes through it. A pattern of disturbance which is caused by the energy that travels away from the source of sound is called a sound wave.

A sound wave is a mechanical wave . A mechanical wave is caused by a vibration of matter and it propagates through a material medium like solid,liquid or gas.It involves the interaction between particles.Since a sound wave is a disturbance which travels through a material medium and also involves particle-particle interaction, it is said to be a mechanical wave.Mechanical waves do not travel through vacuum. Hence , sound waves cannot travel in vacuum.

Longitudinal waves are the one in which displacement of the individual particles of a medium is parallel to direction of propagation of wave.In a fluid medium like gas or liquid, the particles of the medium through which sound travels vibrates parallel to the direction that the sound wave moves. Hence, sound waves are longitudinal waves.When particles of the medium vibrate,they move back and forth. This continous back and forth movement of such particles creates high pressure and low pressure regions. These are termed as compressions and rarefactions respectively. Compressions and rarefactions are created due to these longitudinal vibrations.

A wave in which the propagated disturbance is a variation of pressure in a medium is called a pressure wave.Sound wave is also called a pressure wave because it consists of a repeating pattern of high-pressure and low-pressure regions moving through a material medium.

Parts of a sound wave

Each wave has a highest point to which the medium rises to and it is termed as crest.It is the point on the wave where the displacement of the medium is maximum.The lowest point to which the medium sinks to is called a trough.It is the point on the wave where the displacement of the medium is the minimum.

Characteristics of a sound wave

We hear a variety of sounds in our daily life.They can be soft,loud,pleasant and even annoying.Sound produced by a flute is different from the sound of a guitar. We understand from this that the sound produced by different sources have different features or characteristics.There are five main characteristics of a sound wave. They are




4.Time period

5. Speed


Wavelength is defined as the length between two consecutive crest or trough of a sound wave.It is also the distance between the centres of two successive compressions or rarefactions of the sound wave.In general, it is the length of a complete wave.


where F is the frequency of the wave and v is the speed of the wave.It's SI unit is metre (m).


Amplitude is defined as the magnitude of maximum displacement or disturbance in a sound wave.It is a measure of energy.Particles of the medium get displaced temporarily from their original positions when a wave passes through a medium.The maximum displacement of the particles of the medium from their original mean positions when a wave passes through the medium is called as the amplitude.It is also a measure of the energy. Higher the amplitude, higher is the energy .Loudness and softness of sound is determined by the amplitude of the sound wave.


Frequency is defined as the number of complete waves produced in a second.It is also the number of rarefactions or compressions produced per unit time.It can also be defined as the number of vibrations in a second. It’s SI unit is Hertz (hz).

Time Period

The time taken to produce one complete wave is called as the time period.It is the time taken by a particle in a medium to make one complete vibrational cycle.It’s SI unit is seconds.


The distance travelled by the wave in one second is called as the speed of the sound wave.It is the speed at which the sound propagates through a medium.It’s SI unit is m/s.