The sound is a form of energy and is produced by vibrations. They are longitudinal and mechanical in nature. Sound waves can travel from one medium to another medium and when they do so there will be a change in speed and wavelength but not in frequency. Sound waves with the frequency in the range of (0-20 Hz) are called infrasonic waves. Sound waves with frequency range (20-20000 Hz) are called audible range. Sound waves with the frequency greater than 20000 Hz are called Ultrasonics.

The speed of the sound waves is 332m/sec in air. The speed of the sound wave is minimum in gases and maximum in solids. The speed of sound waves increases in humid conditions and speed of sound increases with the rise in temperature. Sound waves can undergo reflection, refraction, and diffraction.

Relative motion between source and object is called Doppler effect. And this phenomenon helpful in astronomy.SONAR( Sound Navigation And Ranging) is used to measure the depth of the sea.

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