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Propagation of Sound in Various Media


A wave is a disturbance that moves through a medium when the particles of the medium set the neighbouring particles in motion. These in turn produce similar motion in others. The particles themselves do not move but the disturbance is carried forward. Wave motion is produced due to the repeated vibrations of the particles of the medium. This is what happens when sound is propagated through a medium.

When an object vibrates and makes sound, then the air layers around it also start vibrating in exactly the same way and carry sound waves from the sound producing source to our ears. There is no actual movement of the particles from the source to our ears. The particles only vibrate back and forth and transfer sound energy from one to another till it reaches our ears.

The material through which sound travels is known as the medium. The medium can be a solid, liquid or a gas. Sound needs a medium to travel. It cannot travel through vacuum.

If a train is very far away and we cannot see it, we cannot hear the sound through air. But if we place our ears on the railway track, we’ll hear the sound of the approaching train. This shows that sound can travel through solids.

Place a squeaking toy in a plastic bag and immerse it in water. Ask your friend to place his / her ears on the side of the bucket of water and squeeze the toy. Your friend will be able to hear the toy squeak. This shows that sound can travel through liquids also. This fact has been used in the detection of submarines or any other submerged objects under sea. You are able to hear your teacher speak or your friends speak to you because air is the medium through which the sound waves are traveling in this case. Sound cannot travel through vacuum. The bell jar experiment helps to prove this.



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