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 prove by the following 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 the 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.
The aforesaid facts lead to three conclusions. First, sound is produced by vibrations. Second, sound travels in the form of waves. And third, sounds needs a material medium for its propagation.
