Sound Waves and Disturbance in a Medium

Introduction

Sound is produced by vibrating objects and it needs a material medium to propagate. But how does sound actually travel through a medium?

Sound travels through a medium in the form of a disturbance. This disturbance is passed from one particle of the medium to the next particle. In this way, sound travels from the source to the listener.

What is a Sound Wave?

A sound wave is a disturbance that travels through a material medium due to the vibration of particles of the medium.

In a sound wave, the particles of the medium do not travel from the source to the listener. They only vibrate about their mean positions and transfer the disturbance to nearby particles.

Sound wave = Disturbance travelling through a medium

Disturbance in a Medium

When a sound source vibrates, it disturbs the particles of the medium near it. These particles start vibrating and disturb the next particles.

This process continues from one particle to another, and the disturbance travels forward through the medium.

The particles themselves do not move forward with the sound wave. Only the disturbance moves forward.

Slinky Activity to Understand Sound Waves

A slinky is a long flexible spring. It can be used to understand how sound travels through a medium.

Take a slinky and keep it slightly stretched on a table or floor. Ask a friend to hold one end fixed. Now push and pull the other end of the slinky quickly.

You will observe that a disturbance is produced and it travels along the length of the slinky.

Observation in Slinky Activity

  • Some turns of the slinky come closer together.
  • Some turns of the slinky become more spread out.
  • These close and spread-out regions move along the slinky.
  • A marked point on the slinky does not travel forward.
  • The marked point only moves to and fro about its position.

Figure

Disturbance Travelling Through a Slinky Direction of disturbance Marked turn Marked turn moves to and fro, not forward with the wave. Turns closer together Turns more spread out In sound propagation, disturbance travels; particles only vibrate.

Explanation of the Figure

The figure shows a disturbance travelling through a slinky. Some turns of the slinky are closer together, while some turns are more spread out.

These close and spread-out regions move along the slinky. However, a marked turn of the slinky does not travel along with the disturbance. It only moves to and fro about its position.

Sound travels through a medium in a similar way. The disturbance travels forward, but the particles of the medium only vibrate about their mean positions.

How Sound Travels Through Air

Sound travels through air as a disturbance in air particles.

When a vibrating source moves forward, it pushes nearby air particles. These particles move closer together and transfer the disturbance to the next particles.

When the source moves backward, the nearby air particles spread out. In this way, the source produces continuous disturbances in air.

Particles Do Not Travel with the Sound Wave

A very important point is that the particles of the medium do not travel with the sound wave.

For example, when a person speaks, air particles near the person do not travel all the way to your ear. Instead, they vibrate about their mean positions and pass the disturbance to nearby air particles.

Particles vibrate; disturbance travels.

Mean Position of Particles

The mean position is the normal position of a particle when there is no sound disturbance.

When a sound wave passes through a medium, the particles move to and fro about their mean positions.

After the disturbance passes, the particles return to their usual motion.

Sound Wave as Energy Transfer

A sound wave transfers energy from one place to another.

The particles of the medium help in transferring this energy by vibrating and colliding with neighbouring particles.

Thus, in sound propagation, energy travels through the medium, but the particles of the medium do not move permanently from one place to another.

Direction of Propagation

The direction in which a sound wave travels is called the direction of propagation.

In the slinky activity, the disturbance travels along the length of the slinky. Similarly, sound travels through air, water, or solids in the direction of propagation.

Sound from a Source

A sound source may send sound waves in many directions.

For example, when a bell rings in a classroom, students sitting in different directions can hear it. This shows that sound can spread in many directions from a source.

For simple understanding, sound propagation is often shown in one direction, but in real life, sound usually spreads in different directions.

Comparison Between Slinky and Sound Wave

Slinky Model Sound Wave in Air
Turns of slinky act like particles of medium. Air particles act as particles of medium.
Some turns come closer together. Air particles become closer in some regions.
Some turns become more spread out. Air particles become more spread out in some regions.
The disturbance travels along the slinky. The sound disturbance travels through air.
A marked turn only moves to and fro. Air particles only vibrate about mean positions.

Examples from Daily Life

  • When a bell rings, sound travels through air as a disturbance.
  • When a speaker produces music, air particles vibrate and transfer the sound disturbance.
  • When someone speaks, the sound reaches our ears through vibrating air particles.
  • When a drum is beaten, the vibrating membrane creates a disturbance in air.
  • When a tuning fork vibrates, it creates a sound wave in the surrounding air.

Important Terms

1. Sound Wave

A disturbance that travels through a material medium and carries sound energy.

2. Disturbance

A change produced in the medium due to vibration of the sound source.

3. Medium

The material through which sound propagates.

4. Mean Position

The normal position about which particles of the medium vibrate.

5. Direction of Propagation

The direction in which the sound wave travels.

Important Points

  • Sound travels through a medium as a disturbance.
  • A vibrating source creates a disturbance in the surrounding medium.
  • The disturbance is transferred from one particle to another.
  • Particles of the medium do not travel with the sound wave.
  • Particles only vibrate about their mean positions.
  • In a slinky, the disturbance travels but the marked turn only oscillates.
  • Sound waves carry energy from the source to the listener.
  • The direction in which a sound wave travels is called the direction of propagation.
  • Sound can spread in many directions from a source.
  • Sound propagation requires a material medium.

Conclusion

Sound travels through a medium as a disturbance. This can be understood with the help of a slinky. In the slinky, the disturbance travels forward, but the turns of the slinky only move to and fro about their positions. Similarly, in sound propagation, the particles of the medium do not travel with the sound wave. They only vibrate about their mean positions and transfer the disturbance forward. Thus, sound waves carry energy through a medium without the actual flow of particles.

en_USEnglish
hi_INहिन्दी en_USEnglish