Solution

Vibrations of the air particles which can be detected by the ear are known as sound waves. When an object starts vibrating, it forces the adjacent particles of the medium to vibrate. When the vibrating object moves in the forward direction, it compresses the particles of the medium to create a region of high pressure called the compression. However, when it moves in backward direction, it produces a region of low pressure called rarefaction. As the object continues to vibrate in the forward and backward direction, compressions and rarefactions are produced regularly. So, a sound wave is produced which propagates through air.