Speed of Sound

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The speed of sound is often said to be 343m/s, but this is only in very specific conditions – when sound is travelling through air at 20°C.

Air = 20°C
Speed of sound = 343m/s

In other conditions, this value can be very different.

Sound travels over four times faster through water than air.

Speed of sound in water ≈ 1500m/s
Over 4 x faster than through air

Sound waves are pressure disturbances, travelling in waves as they spread through a medium.

The speed is how fast the disturbance passes from one particle to the next – but what affects this?

What affects the speed of sound?

Temperature

The speed of sound increases with temperature.

When molecules are warmed they move faster – this allows them to pass on sound vibrations at a greater rate.

Increased temperature
Increased speed of sound

Elasticity

If the attraction between particles can be thought of as tiny springs, then the attraction of particles in mediums with a higher elasticity is stronger.

As a sound wave passes, these springs would be stretched and pulled back faster than they would in materials with a lower elasticity – letting the wave pass more quickly.

Higher elasticity
Faster speed of sound

This means the state of the medium can have a huge effect – in general, sounds travel faster through solids, which have the strongest interactions between particles followed by liquids, and then gases – which have the weakest interactions.

Density

Sound will generally travel faster through the less dense of two mediums, if they are in the same state, because the mass of each molecule is smaller.

Less energy is required to move the lighter molecules, allowing the sound to travel faster.

Smaller molecular mass
Faster speed of sound

Helium has a lower mass than air, allowing sound to travel nearly three times faster through the lighter gas.

The speed of sound really does depend on various factors.

Temperature
Elasticity
Density

This makes it impossible to determine a definitive speed of sound.