Everything Science Grade 10

CHAPTER 10. SOUND 10.1

Sound waves travel faster through liquids, like water, than through the air because water is
denser than air (the particles are closer together). Sound waves travel faster in solids than
in liquids.

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compressions

rarefactions

vibrating

tuning

fork

column of air in front

of tuning fork

Figure 10.2: Sound waves are pressure waves and need a medium through which to travel.

Tip

A sound wave is

a pressure wave.

This means that

regions of high pres-

sure (compressions)

and low pressure

(rarefactions) are

created as the sound

source vibrates.

These compressions

and rarefactions arise

because the source vi-

brates longitudinally

and the longitudi-

nal motion of air

produces pressure

fluctuations.

Activity: Build your own telephone

Have you ever wondered if you can actually use tin cans or cups to

make a telephone? Try it and see!

What you need:

• Two tin cans or paper paper cups


• String


• Toothpicks or small sticks
  Try This:

1. Tie a toothpick on each end of a length of string.

2. Make a hole in the base of the can or cup. Poke the toothpick

through the end of the can. Pull the string tight so the toothpick

rests on the inside bottom of the can. Put one can at each end

of the string. (You may want to experiment with different cans or

cups and strings or wires to see what works best.)

3. Hold the string tight and talk into one of the cans. The person at

the other end should be able to hear you. Why does the string

have to be tight?

4. Try to make a party line by tying a third string and can or cup

onto the middle of the string. Can everybody talk to everybody

else?

Sound waves need something to travel through. Usually they travel

through air, but they can travel much faster and farther through a string.

The string has to be tight or else the sound wave cannot travel through

it. The cup helps to amplify the sound on the other end.

Physics: Waves, Sound and Light 167