10.2 rate of sound (ESACZ)

The speed of sound depends on the tool the sound is travelling in. Sound travels much faster in solids than in liquids, and faster in liquids than in gases. This is because the thickness of solids is higher than that of liquids which means that the particles are closer together. Sound deserve to betransfer more easily.

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The speed of sound additionally depends on the temperature that the medium. The name is the tool is, the faster its corpuscle move and also therefore the faster the sound will certainly travel through the medium. As soon as we heat a substance, the corpuscle in the substance have more kinetic energy and vibrate or relocate faster. Sound can because of this be sent an ext easily and quickly in hot substances.

Sound tide are pressure waves. The rate of sound will thus be affected by the press of the tool through which it is travelling. At sea level the air press is greater than high increase on a mountain. Sound will certainly travel much faster at sea level wherein the air push is greater 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 speed of sound in air, at 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 total or anything the can develop a according to sound in an answer to clearly shows action



The rate of sound can be measured since light travel much much faster than sound. Irradiate travels at around ( ext300 000) ( extm·s$^-1$) (you will learn more about the speed of light in the next chapter) if sound just travels at around ( ext300) ( extm·s$^-1$). This difference way that end a distance of 300 m, the irradiate from an occasion will reach her eyes nearly instantly yet there will certainly be an approximate fifty percent a second lag before you hear the sound produced. Therefore if a starter"s pistol is fired indigenous a good distance, girlfriend will check out the smoke automatically but there will be a lag before you hear the sound. If you know the distance and the time climate you have the right to calculate the speed (distance separated by time). Girlfriend don"t require a gun yet anything that you can see creating a loud sound.

Try this:

Find a location where you understand the precise, straight-line distance between two point out (maybe an 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 prevent watches

The human being with the stopwatch should start the stopwatch as soon as they view the other human make the sound and stop the stopwatch once they hear the sound (do this a couple of times and write the time down)


You can now calculation the speed to sound by splitting the street by the time. Mental to occupational in S.I. Units (metres and also seconds). If you took multiple readings climate you can sum them and divide by the number of readings to get an mean time reading. Use the typical 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 can test this by starting it and then make the efforts to protect against it immediately.

What to be the forecast temperature ~ above the job of the measurement?

Was the humid or really dry?

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

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

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Reflection and echoes (ESADA)

When the sound waves collide with things they space reflected. You deserve to think of the individual particles that space oscillating about their equilibrium position colliding into the object when the wave passes. They bounce turn off the object resulting in the wave to be reflected.

In a an are with many little objects there room reflections in ~ every surface but they are too little and too mixed up to have an end result that a human can hear. However, once there is an open an are that has actually only huge surfaces, for example a institution hall that is empty, climate the reflect sound have the right to actually it is in heard. The sound tide is reflected in such a tide that the tide looks the same but is relocating in the contrary direction.

This method that if you stand in a hall and loudly say “hello” you will certainly hear yourself say “hello” a split 2nd later. This is an echo. This can likewise happen out in a large open room with a huge reflecting surface nearby, choose standing close to a mountain cliff in one area v no trees or bushes.

This is a very useful residential or commercial property of waves.

See more: How Many Fluid Ounces In One Quart S To Fluid Ounces Conversion

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Ships ~ above the ocean exploit the showing properties that sound tide to recognize the depth that the ocean. A sound tide is transmitted and also bounces off the seabed. Since the speed of sound is known and the time lapse in between sending and also receiving the sound can be measured, the street from the ship to the bottom that the ocean deserve to be determined, This is dubbed sonar, which is an acronym for Sound Navigation And Ranging.

Worked example 1: SONAR

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

Identify what is given and also what is gift 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 choose dolphins and also bats make use of sounds tide to find their way. As with ships on the ocean, bats usage sonar to navigate. Waves that are sent are reflected turn off the objects roughly the animal. Bats, or dolphins, then use the reflected sound to type a “picture” of their surroundings. This is dubbed echolocation.