Sound is the movement of energy through substances in longitudinal (compression/rarefaction) waves.
Sound is produced when a force causes an object or substance to vibrate — the energy is transferred through the substance in a wave. Typically, the energy in sound is far less than other forms of energy.
Let's see this illustration.
A vibrating drum in a disco transfers energy to the room as sound. Kinetic energy from the moving air molecules transfers the sound energy to the dancers eardrums. Notice that Kinetic (movement) energy in the sticks is being transferred into sound energy.
Sound vibrations create sound waves which move through mediums such as
air and water before reaching our ears.
The diagram below shows how a sound wave is represented:
Sound energy is usually measured by its' pressure and intensity, in special units called pascals and decibels. Sometimes, loud noise can cause pain to people. This is called the threshold of pain. This threshold is different from person to person. For example, teens can handle a lot higher sound pressure than elderly people, or people who work in factories tend to have a higher threshold pressure, because they get used to loud noise in the factories.