10.2 speed 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 also faster in liquids 보다 in gases. This is since the density of solids is greater than the of liquids which way that the particles space closer together. Sound deserve to be sent much more easily.

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The rate of sound also depends ~ above the temperature the the medium. The hotter the medium is, the much faster its particles move and also therefore the faster the sound will certainly travel through the medium. Once we warmth a substance, the particles in that substance have an ext kinetic energy and also vibrate or move faster. Sound can as such be transmitted an ext easily and quickly in name is substances.

Sound tide are pressure waves. The speed of sound will thus be affected by the press of the medium through which it is travelling. At sea level the air push is higher than high increase on a mountain. Sound will certainly travel faster at sea level where the air pressure is greater than it would 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 different materials.

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

Measuring the speed of sound in air


To measure up the rate of sound.


Starter"s pistol or anything that can develop a loud sound in response to clearly shows action



The speed of sound deserve to be measured since light travel much much faster than sound. Irradiate travels at about ( ext300 000) ( extm·s$^-1$) (you will certainly learn an ext about the speed of light in the following chapter) while sound only travels at about ( ext300) ( extm·s$^-1$). This difference method that end a street of 300 m, the light from an event will reach her eyes practically instantly but there will certainly be one approximate fifty percent a 2nd lag before you hear the sound produced. Therefore if a starter"s pistol is fired native a an excellent distance, friend will see the smoke immediately but there will certainly be a lag prior to you hear the sound. If you understand the distance and also the time climate you have the right to calculate the speed (distance separated by time). Girlfriend don"t need a gun but anything that you have the right to see creating a loud sound.

Try this:

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

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

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

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


You deserve to now calculation the rate to sound by dividing the street by the time. Remember to work in S.I. Systems (metres and seconds). If you take it multiple readings then you can sum them and also divide by the variety of readings to get an mean time reading. Use the mean time to calculation the speed:


Time (s)

Distance (m)

( extm·s$^-1$)


Some questions to ask:

What is your reaction time on the stopwatch? You deserve to test this by beginning it and then make the efforts to avoid it immediately.

What was the projection temperature top top the job of the measurement?

Was it humid or very dry?

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

You can vary this experiment through trying it on days when the weather is various as this can change air pressure and temperature.

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Reflection and also echoes (ESADA)

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

In a room with many tiny objects there room reflections at every surface but they are too small and too mixed up to have an outcome that a human have the right to hear. However, when there is an open room that has actually only big surfaces, for example a college hall the is empty, then the reflected sound have the right to actually be heard. The sound tide is reflect in together a wave that the tide looks the same yet is moving in opposing direction.

This means that if you was standing in a hall and loudly say “hello” you will hear you yourself say “hello” a split 2nd later. This is one echo. This can additionally happen the end in a large open room with a big reflecting surface ar nearby, like standing close to a mountain cliff in one area through no tree or bushes.

This is a an extremely useful home of waves.

See more: What Are Social Costs Of Cell Phone Usage ? Support Your Answer

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Ships ~ above the ocean manipulate the reflecting properties the sound waves to identify the depth that the ocean. A sound wave is sent 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 also receiving the sound have the right to be measured, the distance from the delivery to the bottom the the ocean can be determined, This is referred to as sonar, which is an acronym because that Sound Navigation And Ranging.

Worked instance 1: SONAR

A ship sends a signal come the bottom of the s to recognize the depth the the ocean. The rate 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 that point?

Identify what is given and also 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 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 manipulate sounds waves to discover their way. Similar to ships top top the ocean, bats use sonar to navigate. Waves that are sent out are reflected turn off the objects approximately the animal. Bats, or dolphins, then use the reflected sound to kind a “picture” of your surroundings. This is called echolocation.