Acoustics is the science of sound.

An "elastic media" is one that vibrates if impacted by a force—it will move in one direction and return to its original position. Examples are a string that has been plucked or a tuning fork that has been struck. Liquids and gases can be elastic media, too, and vibrations can be set up in them by forces on them--pressure.

Sound is vibrations in air, a pressure wave that causes the atoms of air to vibrate back and forth, transmitting the pressure along. The same principle works in liquids and solids, too, and sound can be also be transmitted through them. All that is necessary for sound is for some object--a vocal cord, a violin string, the blow of a hammer--to start a displacement in an elastic medium. The medium then transmits the sound via waves of high and low pressure...