10.2 rate of sound (ESACZ)

The rate of sound relies on the medium the sound is travelling in. Sound travels faster in solids 보다 in liquids, and faster in liquids than in gases. This is due to the fact that the thickness of solids is greater than the of liquids which means that the particles are closer together. Sound deserve to be sent an ext easily.

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The rate of sound also depends on the temperature of the medium. The name is the tool is, the faster its corpuscle move and therefore the faster the sound will travel v the medium. As soon as we warm a substance, the corpuscle in that substance have more kinetic energy and also vibrate or relocate faster. Sound can therefore betransfer more easily and quickly in name is substances.

Sound tide are press waves. The speed of sound will as such be affected by the push of the medium through which it is travelling. At sea level the air push is greater than high increase on a mountain. Sound will certainly travel quicker at sea level where the air press is greater than it would certainly at places 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, in ~ sea level, in ~ a temperature the 21℃ and under typical atmospheric conditions, is ( ext341) ( extm·s$^-1$).

Measuring the rate of sound in air


To measure the speed of sound.


Starter"s gun or anything the can create a according to sound in response to visible action



The rate of sound deserve to be measured since light travels much quicker than sound. Irradiate travels at around ( ext300 000) ( extm·s$^-1$) (you will certainly learn an ext about the speed of irradiate in the next chapter) when sound just travels at around ( ext300) ( extm·s$^-1$). This difference method that over a distance of 300 m, the light from an event will reach her eyes virtually instantly but there will certainly be one approximate half a 2nd lag before you hear the sound produced. Thus if a starter"s pistol is fired from a an excellent distance, you will check out the smoke immediately but there will certainly be a lag before you hear the sound. If you recognize the distance and also the time then you have the right to calculate the rate (distance split by time). Girlfriend don"t require a gun but anything that you deserve to see developing a loud sound.

Try this:

Find a location where you recognize the precise, straight-line distance in between two point out (maybe an athletics track)

Someone requirements to was standing at the one suggest to develop the sound

Another person needs to was standing at the other suggest with the protect against watches

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


You deserve to now calculate the rate to sound by dividing the distance by the time. Remember to occupational in S.I. Devices (metres and also seconds). If you take it multiple readings then you can sum them and also divide by the variety of readings to obtain an typical time reading. Usage the median time to calculation the speed:


Time (s)

Distance (m)

( extm·s$^-1$)


Some questions to ask:

What is her reaction time top top the stopwatch? You can test this by beginning it and then trying to protect against it immediately.

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

Was that humid or really dry?

Discuss what might change the speed of sound the you measured.

You can vary this experiment through trying it on days once the weather is different as this can readjust air pressure and temperature.

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Reflection and echoes (ESADA)

When the sound waves collide with an item they space reflected. You have the right to think of the individual corpuscle that room oscillating about their equilibrium position colliding right into the object once the tide passes. Lock bounce off the object resulting in the tide to be reflected.

In a room with many small objects there are reflections in ~ every surface but they are too small and too blended up to have an end result that a human can hear. However, once there is an open space that has actually only large surfaces, for instance a college hall that is empty, climate the reflect sound deserve to actually be heard. The sound tide is reflect in such a wave that the wave looks the same but is relocating in opposing direction.

This means that if you was standing in a hall and loudly speak “hello” you will hear you yourself say “hello” a split 2nd later. This is an echo. This can additionally happen outdoors in a large open space with a large reflecting surface nearby, favor standing close to a hill cliff in one area through no tree or bushes.

This is a an extremely useful property of waves.

See more: How Many Degrees In A Parallelogram, How Many Degrees Is A Parallelogram

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Ships on the ocean manipulate the reflecting properties that sound waves to identify the depth of the ocean. A sound tide istransfer and also bounces turn off the seabed. Due to the fact that the rate of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the delivery to the bottom that the ocean can be determined, This is dubbed sonar, i m sorry is one acronym because that Sound Navigation And Ranging.

Worked example 1: SONAR

A ship sends out a signal to the bottom of the s to identify the depth the the ocean. The speed of sound in sea water is ( ext1 450) ( extm·s$^-1$). If the signal is got ( ext1,5) ( extseconds) later, just how deep is the ocean at that 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 also back \ herefore t & = ext0,75 ext seconds ext one way \ D & = ? endalign*

Calculate the distance

eginalign* extDistance & = ext speed 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 also bats exploit sounds tide to uncover their way. As with ships top top the ocean, bats usage sonar come navigate. Waves the are sent out are reflected off the objects around the animal. Bats, or dolphins, then use the reflected sounds to form a “picture” of their surroundings. This is dubbed echolocation.