Speed of Sound in Air

Sound travels by molecular collisions, and warmer molecules move faster, passing the disturbance along more quickly. In dry air the speed starts at 331.3 m/s at 0 °C and gains about 0.606 m/s per degree: 343 m/s in a 20 °C classroom, 349 m/s on a 30 °C summer day, but only 325 m/s in −10 °C winter air. The linear formula is an excellent approximation of the true √T dependence across everyday temperatures.

You use this physics every thunderstorm: light arrives essentially instantly, so counting seconds between flash and rumble and dividing by three gives the storm's distance in kilometres (sound covers about 1 km every 2.9 s at 20 °C). The temperature dependence has audible consequences too: sound bends toward where it travels slower, so on a cold, still morning with warm air above a chilled ground layer, wavefronts curve back down toward the earth and a distant train sounds uncannily close. Orchestras feel it as well: a flute's pitch rides on v, drifting sharp as the concert hall warms through the evening.