How The Speed of Sound Changes In Different Materials

The speed that sound travels largely depends on the material type.

For example, sound waves travel fastest when they are moving through solids and tend to travel a lot slower when moving through gases and liquids.

This is a very broad summary as it’s not only the type of material that makes a difference to the speed the sound is moving at; the density, elastic property and even the temperature can have an impact too.

So, how fast does sound travel through different materials? Let’s take a look!

Gases

Material Speed (m/s)

Air at 20 degrees Celsius

343 m/s

Air at 40 degrees Celsius

355 m/s
Helium

972 m/s

Hydrogen 1,286 m/s

Liquids

Material Speed (m/s)
Mercury 1,450 m/s

Water

1,493 m/s
Sea water 1,533 m/s
Glycerol 1,904 m/s

Solids

Material Speed (m/s)

Rubber

60 m/s

Lead

1210 m/s

Gold

3240 m/s

Brick

4200 m/s

Glass

4540 m/s

Copper

4600 m/s

Brass

4,700 m/s
Steel 5,050 m/s
Aluminium 6,320 m/s
Diamond 12,000 m/s

 

The tables above display the speed of sound in liquid, gas and solid materials ranking from slowest to fastest.

As you can see, there is a huge difference in how fast speed travels depending on the material, from 343 m/s through air to 1,493 m/s through water up to 12,000 m/s through diamond.

So, why does sound travel at different speeds depending on the material?

What is sound?

accelerating soundwaves

First of all, we need to know what sound actually is to understand how it moves.

Sound is kinetic energy that is vibrating through molecules.

If the molecules are closer together then the sound can travel between them more easily and quickly.

If the molecules are further apart and less tightly bonded then it is harder for the sound to travel and as a result the sound travels slower.

This is why the speed of sound is faster in solids than in liquids and gases.

However, elastic properties and temperature also impact the speed that sound travels.

Key Factors That Impact the Speed of Sound

a noisy concert

The table clearly shows it is not just whether a material is solid or liquid that impacts the speed that sound can travel through it.

The following factors also have an effect:

·        Density

As we mentioned above, the density of an object impacts the speed that sound can travel through it.

It is because of this that sound can travel faster in gases that are denser. If we take a look at hydrogen as an example, it is denser than oxygen and therefore allows the sound to travel faster.

·        Elastic Properties

This basically refers to how a material holds its shape when force is applied, if the material has high elastic properties then it is able to easily return to its normal shape after pressure is applied.

Materials with higher elastic properties allow sound to travel through them more easily than materials with lower elastic properties.

It is more likely that materials with lower elastic properties will absorb the sound rather than carry it.

As an example, lead has high elastic properties compared to rubber and therefore allows the sound to travel much faster.

·        Temperature

Earlier we mentioned that temperature can also impact the speed of sound.

This depends on the material group as gases tend to behave a little differently when it comes to temperature.

We have mentioned that sound travels faster when molecules are closer together so surely that means colder gases allow sound to travel faster than warmer gases, right?

Although theoretically when gas is colder it brings molecules closer together which should make it easier and quicker for the sound to travel, a temperature increase causes increased vibrations and this movement of the molecules that occurs in hotter gases actually allows sound to travel more quickly.

Therefore, when the temperature is higher in gases sound is able to travel faster.

For example:

At -1 degree Celsius sound travels at 330.4 m/s, at 21 degree Celsius sound travels at 343.6 m/s and at 45 degrees Celsius sound travels at 358 m/s.

The sound has travelled faster through air because the increased temperature has increased the vibrations of the molecules.

Speed of Sound in Gases and Liquids

The speed of sound travelling through gases and liquids is considerably slower than the majority of solids we have listed.

That is due to the molecules being a lot less rigid in liquids and gases which causes a decrease in the elastic properties of those materials.

The molecules in liquids are further apart than in solids, and the molecules in gases are even further apart and this is why sound struggles to travel fast through these materials.

Using Material to Stop Sound

a noisy band playing live music

You may be reading this and thinking that sound doesn’t seem to travel that well through the walls and doors of your home anyway but this is because most of the time the sound waves have to first travel through the air and then through the solid material which means some of the sound will have already been lost before it even hits the door/ wall.

A proportion of the sound will most likely be reflected back into the room through the air too but when you think about the sound of someone knocking on a door – it travels very well through the solid material.

This is why it can be very effective to soundproof a kennel or a dog crate with material that doesn’t let sound travel well because the sound already needs to travel through the air (which is difficult) and then it will meet a material that it cannot travel through well and the sound will be absorbed rather than passed on.

Using Rubber for Sound-Absorbing / Proofing

As you can see in the table, sound travels at 60 m/s through rubber.

This was the lowest reading from the whole table and is the reason that rubber is considered to be one of the best soundproofing materials.

The rubber will absorb most of the sound rather than carrying it which means less of the sound will be transmitted past the rubber.

Whereas other material types won’t be as effective in reducing the sound as they allow the sound to travel easily and quickly.

Speed of Sound Summary

The speed of sound can vary greatly depending on the material it is travelling through.

This is why it is so important to know more about materials before choosing them for a certain task e.g. soundproofing or noise reduction.

The general properties of gases, liquids and solids help to determine the speed of sound but it is the specific density and elastic properties of the material in question which truly determine the sound the speed can travel.

This is why we see such variation in the table of solids.

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