The speed of sound is the distance traveled per unit of time by a sound wave as it propagates through an elastic medium. In air at 20°C (68°F), the speed of sound is about 343 meters per second (m/s), or 1,235 kilometers per hour (km/h). This speed depends strongly on the temperature as well as the medium through which the sound travels. Sound travels slowest in gases, faster in liquids, and fastest in solids. For example:
- In dry air at 0°C, the speed of sound is about 331 m/s.
- In water (a liquid), it is about 1500 m/s.
- In wood (a solid), it can be around 3900 m/s.
The speed of sound in air increases with temperature according to the approximate formula v=331 m/s×T273v=331\text{ m/s}\times \sqrt{\frac{T}{273}}v=331 m/s×273T, where TTT is the absolute temperature in Kelvin. Humans observe phenomena such as the delay between lightning and thunder due to the slower speed of sound compared to light. Overall, the speed of sound is a fundamental physical quantity describing how fast vibrations move through a medium.