<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The speed of sound is the distance travelled per unit time by a sound wave as it propagates through an elastic medium . In dry air at 0 ° C (32 ° F), the speed of sound is 331.2 metres per second (1,087 ft / s; 1,192 km / h; 741 mph; 644 kn). At 20 ° C (68 ° F), the speed of sound is 343 metres per second (1,125 ft / s; 1,235 km / h; 767 mph; 667 kn), or a kilometre in 2.91 s or a mile in 4.69 s . </P> <P> The speed of sound in an ideal gas depends only on its temperature and composition . The speed has a weak dependence on frequency and pressure in ordinary air, deviating slightly from ideal behavior . </P> <P> In common everyday speech, speed of sound refers to the speed of sound waves in air . However, the speed of sound varies from substance to substance: sound travels most slowly in gases; it travels faster in liquids; and faster still in solids . For example, (as noted above), sound travels at 343 m / s in air; it travels at 1,484 m / s in water (4.3 times as fast as in air); and at 5,120 m / s in iron (about 15 times as fast as in air). In an exceptionally stiff material such as diamond, sound travels at 12,000 metres per second (26,843 mph); (about 35 times as fast as in air) which is around the maximum speed that sound will travel under normal conditions . </P>

The speed of sound wave in air depends on