Whatever we hear with our ears is called ‘sound’ In scientific language, sound is a kind of disturbance which produces sensations in the ears. Like heat and light, sound is also a form of energy Do you know how sound is produced and how it travels from one place to another? A body produces sound when a part or the whole of it vibrates. When we strike a bell, vibrations are produced in it making sound. If we touch a ringing bell with our hands, we can easily perceive the vibrations in it. Whenever a living being speaks, the diaphragm in his throat vibrates Sound can never be produced without vibrations.
Whenever a body vibrates, sound waves originate from it and travel in a medium. When these waves reach our ears we hear the sound. Our ears are sensitive to sounds which are produced by vibrations of frequencies ranging between 20 and 20,000 hertz. Human ears cannot perceive frequencies of less than 20 and more than 20.000 hertz.
Sound travels from one place to another in the form of waves which need a material medium. They cannot travel in vacuum. This fact can be proved by the following simple experiment.
Take a glass bottle without bottom and connect it to a vacuum pump. a cork on its mouth. Suspend an electric bell inside this bottle. Connect the bell to a battery. It starts ringing and we hear the sound very clearly. Now start evacuating the air from the bottle with the help of the vacuum pump. As the amount of air in the bottle starts decreasing, the intensity of sound also decreases proportionally. When all the air is sucked out of the bottle we do not hear any sound. It is clear from this experiment that a medium is always necessary for the propagation of sound waves.