Quirks & Quarks

Does the speed of sound change with temperature?

Sound travels faster in hotter air as high energy air molecules carry the sound more quickly

Sound travels faster in hotter air as high energy air molecules carry the sound more quickly

Even sound moves more slowly in the cold (Colin Butler/CBC)
Listen2:45

This week's question comes from David Setter in Portland, Oregon. He asks:

Does air temperature affect the speed of sound?

Kim Strong, a professor of physics at the University of Toronto says the answer is yes, in fact sound travels faster when the air is hotter.

At 25 C, the speed of sound is 1,246 kilometres per hour. On a cold day, when the temperature is minus 25, the speed of sound would be about 1,137 kilometres per hour, or about 10 per cent slower. The speed of sound changes by about .6 metres per second for every degree.

Sound is transmitted through the air by compression waves, which, at a small scale, depend on molecules transferring energy one to another. Air molecules have more energy at higher temperatures, which means they vibrate faster. This allows the sound waves to also travel faster because they are propelled by collisions between the molecules.

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