10.2 speed of sound (ESACZ)

The speed of sound depends on the medium the sound is travelling in. Sound travels faster in solids 보다 in liquids, and also faster in liquids than in gases. This is because the density of solids is greater than the of liquids which method that the particles are closer together. Sound can betransfer an ext easily.

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The speed of sound additionally depends ~ above the temperature the the medium. The hot the medium is, the quicker its corpuscle move and also therefore the quicker the sound will travel with the medium. Once we warmth a substance, the particles in that substance have much more kinetic energy and also vibrate or move faster. Sound can therefore be sent much more easily and also quickly in hot substances.

Sound waves are push waves. The rate of sound will therefore be affected by the pressure of the medium through which the is travelling. In ~ sea level the air push is higher than high up on a mountain. Sound will travel quicker at sea level wherein the air press is higher than it would certainly at locations high over sea level.


v (( extm·s$^-1$))


( ext6 420)


( ext3 650)


( ext4 760)


( ext5 100)


( ext3 240)


( ext2 160)

water, sea

( ext1 531)

air, 0℃

( ext331)

air, 20℃

( ext343)

Table 10.1: The speed of sound in various materials.

The rate of sound in air, at sea level, in ~ a temperature that 21℃ and under normal atmospheric conditions, is ( ext341) ( extm·s$^-1$).

Measuring the rate of sound in air


To measure the rate of sound.


Starter"s pistol or anything the can create a loud sound in response to visible action



The rate of sound deserve to be measured since light travels much much faster than sound. Irradiate travels at about ( ext300 000) ( extm·s$^-1$) (you will learn an ext about the rate of light in the next chapter) when sound only travels at about ( ext300) ( extm·s$^-1$). This difference method that over a distance of 300 m, the light from an occasion will reach her eyes practically instantly but there will certainly be one approximate fifty percent a second lag prior to you hear the sound produced. Thus if a starter"s pistol is fired from a great distance, girlfriend will view the smoke immediately but there will certainly be a lag before you hear the sound. If you recognize the distance and the time then you can calculate the rate (distance divided by time). Girlfriend don"t need a gun yet anything that you have the right to see developing a loud sound.

Try this:

Find a location where you recognize the precise, straight-line distance between two clues (maybe one athletics track)

Someone demands to stand at the one point to create the sound

Another human needs to was standing at the other suggest with the avoid watches

The human with the stopwatch must start the stopwatch when they check out the other human being make the sound and also stop the stopwatch once they hear the sound (do this a few times and write the time down)


You deserve to now calculate the rate to sound by splitting the street by the time. Mental to work in S.I. Devices (metres and seconds). If you take it multiple readings climate you can sum them and divide by the number of readings to obtain an typical time reading. Usage the average time to calculation the speed:


Time (s)

Distance (m)

( extm·s$^-1$)


Some questions to ask:

What is her reaction time on the stopwatch? You deserve to test this by starting it and also then do the efforts to stop it immediately.

What to be the projection temperature top top the day of the measurement?

Was it humid or an extremely dry?

Discuss what might readjust the rate of sound that you measured.

You deserve to vary this experiment by trying the on days when the weather is different as this can readjust air pressure and also temperature.

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Reflection and echoes (ESADA)

When the sound tide collide with an item they are reflected. You have the right to think the the individual particles that room oscillating about their equilibrium position colliding right into the object when the tide passes. Castle bounce turn off the object resulting in the wave to be reflected.

In a room with many tiny objects there are reflections in ~ every surface but they are too little and too blended up to have result that a human have the right to hear. However, when there is one open room that has actually only huge surfaces, for instance a college hall the is empty, then the reflect sound can actually it is in heard. The sound wave is reflect in together a tide that the wave looks the same however is moving in the opposite direction.

This way that if you stand in a hall and loudly to speak “hello” you will certainly hear yourself say “hello” a split 2nd later. This is one echo. This can additionally happen outdoors in a broad open room with a huge reflecting surface ar nearby, favor standing near a hill cliff in one area with no trees or bushes.

This is a really useful residential property of waves.

See more: Which Four Elements Comprise 96 Of The Body, Chemical Elements Of The Human Body

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Ships top top the ocean make use of the mirroring properties of sound waves to recognize the depth that the ocean. A sound tide is transmitted and bounces turn off the seabed. Because the rate of sound is known and the time lapse between sending and also receiving the sound can be measured, the street from the delivery to the bottom of the ocean can be determined, This is called sonar, i beg your pardon is one acronym for Sound Navigation And Ranging.

Worked example 1: SONAR

A ship sends a signal come the bottom that the ocean to recognize the depth of the ocean. The speed of sound in sea water is ( ext1 450) ( extm·s$^-1$). If the signal is obtained ( ext1,5) ( extseconds) later, how deep is the ocean at the point?

Identify what is given and what is being asked

eginalign* s & = ext1 450 ext m·s$^-1$ \ t & = ext1,5 ext seconds ext there and back \ herefore t & = ext0,75 ext seconds ext one way \ D & = ? endalign*

Calculate the distance

eginalign* extDistance & = ext rate imes ext time \ D & = s imes t \ & = ( ext1 450 ext m·s$^-1$)( ext0,75 ext s) \ & = ext1 087,5 ext m endalign*
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Echolocation (ESADC)

Animals like dolphins and bats exploit sounds waves to find their way. As with ships ~ above the ocean, bats use sonar to navigate. Waves the are sent out are reflected off the objects roughly the animal. Bats, or dolphins, then use the reflected sound to type a “picture” of your surroundings. This is dubbed echolocation.