Sound is vibration transmitted through solid, liquid, or gaseous matter; particularly, sound means those vibrations composed of frequencies capable of being detected by ears. The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter, gases, liquids, and solids, as longitudinal or transverse (solid) waves. The matter that supports the sound is called the medium. Sound cannot travel through vacuum. Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound wave converts back and forth between the potential energy of the extra compression or lateral displacement strain of the matter and the kinetic energy of the oscillations of the medium.
The speed of sound depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20°C (68°F) air at sea level, the speed of sound is approximately 343 m/s (767.3 mph). In fresh water, also at 20°C, the speed of sound is approximately 1482 m/s (3,315.1 mph).