Explain how bell rings in school

Air is the commonest material through which sound propagates. When a vibrating object, like prongs of tuning fork, move forward, they push the molecules of the air in front of them. This is turn compresses the air, thus creating a region of high pressure and high density called compression. This compression in the air travels forward. When the prongs of the tuning fork move backward, they create a region of low pressure in the air, commonly called rarefaction. This region has low-pressure low density and more volume. As the tuning fork continues to vibrate, the regions of compression in the air alternate with the regions of rarefaction. These regions alternate at the same place. The energy of vibrating tuning fork travels outward. This energy which reaches the ears makes the eardrums to vibrate and thus we hear the sound.