Neha Kishor
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The vibration that propagates as an acoustic wave, through a transmission medium such as a solid,liquid or gas is known as sound. Only acoustic waves that have frequencies in the audio frequency range, that is frequencies lying between about 20 Hz and 20 kHz, elicit an auditory percept in humans. Ultrasound Sound waves are sound waves above 20 kHz. They are not audible to humans. Infrasound waves are sound waves below 20 Hz. The range of hearing may vary for different animal species.Sound waves are longitudinal waves which are transmitted through gases, plasma, and liquids. These are also called compression waves and it requires a medium to propagate. It can be transmitted as both longitudinal waves and transverse waves through solids.If the pressure deviations from the equilibrium pressure are alternating they are longitudinal sound waves.Moreover it causes local regions of compression and rarefaction. The waves of alternating shear stress at right angles to the direction of propagation are called transverse waves.

Even though there are many difficulties relating to the transmission of sounds, at the point of reception sound is readily divisible into two simple elements that is pressure and time and these fundamental elements form the basis of all sound waves.


There are different types of sound like audible, inaudible, pleasant, and unpleasant.

  • Infrasonic waves- The waves with frequency ranges below 20Hz are called infrasonic waves. The waves that are used for the detection of an earthquake, volcanic eruption etc are some of the examples of infrasonic waves.
  • Ultrasonic waves- The waves with frequency ranges above 20kHz are called ultrasonic waves. The waves that are used by some animals to locate their prey and communicate like bats, etc are some of the examples of ultrasonic waves.
  • The waves having a frequency between 20Hz to 20kHz are audible to humans.


Sound is produced by the vibration of an object  that is due to the rapid to and fro movement of an object.The object that is set to vibration disturbs the equilibrium state of the particles in the medium. As a result vibration keeps transmitting from one particle to another. 

As long as the body’s vibration remains the emission of sound continues. This sound generates a hearing experience in our ears by traveling across a continuous elastic membrane. For example when a tuning fork is struck, it vibrates and emits sound and if it is touched with your hand the vibration will stop. As a result, the output of sound will be reduced. Thus we can say the vibration of a body generates sound. Or in other words we can say that the vibration of the body is the primary generator of all types of sound. As a result of vibration mechanical energy is converted into sound.

Propagation of sound

propogation of sound

 Propagation of sound is the traveling of sound from the sound source to the surrounding medium. As there are no molecules present to set vibration, sound waves cannot travel in a vacuum. Or in other words we can say sound always requires a medium to travel from one point to another. In case of vibration of guitar strings we hear the music produced as the vibration produced travels through the air to our ears. Here air acts as a medium of transmission of sound.

How can we hear sound?

types of

When sound waves travel through a medium  and reach our ears we hear the sound. Sound waves are gathered by the pinna of our ear and then lead to the ear canal where they strike the eardrum. The vibration set from the eardrum is transmitted   finally to the inner ear. The sensitive cells present in the inner ear transmits  the vibration to the brain through the auditory nerve which is registered as sound by the brain.

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Check your knowledge

There are two basic types of wave, transverse and longitudinal, differentiated by the way in which the wave is propagated.

Sound is a type of energy made by vibrations. These vibrations create sound waves which move through mediums such as air, water and wood. When an object vibrates, it causes movement in the particles of the medium. This movement is called sound waves, and it keeps going until the particles run out of energy.

Since sound is a wave, it has all of the properties attributed to any wave, and these attributes are the four elements that define any and all sounds. They are the frequency, amplitude, wave form and duration, or in musical terms, pitch, dynamic, timbre (tone color), and duration.

Solids, liquids, and gases all transmit sound as energy waves. Sound energy is the result when a force, either sound or pressure, makes an object or substance vibrate. That energy moves through the substance in waves. Those sound waves are called kinetic mechanical energy.


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