ICSE Class 7 Answered

(i) Sound propagates through the medium as a series of compressions and rarefactions.

When a vibrating object moves forward it pushes and compresses the air in front of it creating a region of high pressure (compression).

When the vibrating object moves backwards it creates a region of low pressure (rarefaction)

(ii)

 

(iii) Sound waves are called longitudinal waves as the particles of the medium vibrate in a direction parallel to the direction of propagation of the wave.