Speed of Sound

Does sound travel faster through air, water or steel? Send a pulse down five tracks at once and see which one wins the race.

Air
291.5 ms
Water
67.6 ms
Steel
16.8 ms
Steel vs air
17.4× faster

The maths, live

Air t = d ÷ vt = 100 ÷ 343 = 291.5 ms
Helium t = d ÷ vt = 100 ÷ 1007 = 99.3 ms
Water t = d ÷ vt = 100 ÷ 1480 = 67.6 ms
Wood t = d ÷ vt = 100 ÷ 3850 = 26.0 ms
Steel t = d ÷ vt = 100 ÷ 5960 = 16.8 ms

Sound is particles bumping into their neighbours. In stiff solids like steel the particles are tightly linked, so the push passes along much faster than in air.

How it works

Sound passes along a material as each particle pushes on the next. In air, at 20 °C, it travels about 343 m/s. In water it's about 1480 m/s, along the grain of oak wood about 3850 m/s, and in steel about 5960 m/s, more than 17 times faster than in air.

Solids and liquids carry sound fast because their particles are packed close together and held tightly, so a push is passed on almost straight away. Helium is a gas like air, but its particles are much lighter and zip about faster, so sound goes about three times faster in helium than in air.

Try this

  1. Over 100 m, how much sooner does the sound arrive through steel than through air?
  2. Which is faster: helium or water?
  3. If you put your ear to a long metal railing and someone taps the far end, why might you hear two taps?