How does sound travel?

          Whatever we hear with our ears is called ‘sound’. In scientific terms, sound is a kind of disturbance which produces sensations in the ears. Like heat and light, sound is also a form of energy. Do 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 that create sound: If we touch a ringing bell with our hands, we can easily feel 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 emanate 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 to 20,000 hertz. Human ears cannot perceive frequencies of less than 20 hertz 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 can be proved by a simple experiment.

          Take a glass bottle without bottom and connect it to a vacuum pump. Put 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 proportionately. When all the air is sucked out of the bottle we do not hear any sound. This experiment proves that a medium is always necessary for the propagation of sound waves.

          The aforesaid facts lead to three conclusions. First, sound is produced by vibrations. Second, sound travels in the form of waves. And third, sound needs a material medium for its propagation. Sound can travel through gases, liquids and solids. It travels fastest in solids, followed by liquids and slowest in gases. It cannot travel in space because there is no material medium present there. That is why astronauts talk to each other with the help of radio sets.