8 l sound & hearing (boardworks)

KS3 Physics

8L Sound and
Hearing
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© Boardworks Ltd 2004
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Contents

8L Sound and Hearing
What is sound?
Speed of sound
Reflecting sound
The ear and hearing
Summary activities
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What causes sound?
Take a tuning fork and strike it
against a block of wood.
What do you observe?
The tuning fork vibrates
and you hear a sound.

Sounds are made when
an object vibrates.

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Good vibrations!
What vibrates so that the following make sounds?
violin
strings

drum
skin

voice box
loudspeaker
cone
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The bell-jar experiment
Place a ringing clock inside the bell jar and what happens?
There is air inside the bell jar
so the sound can travel and be heard.

vacuum
pump on

Remove the air from the bell jar
and what happens to the sound?
The sound cannot be heard
because there is no air inside
the bell jar (a vacuum).

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Studying sound waves
Sound waves can be studied with this type of equipment.
loudspeaker
oscilloscope
signal generator

A loudspeaker
converts
signals from
the signal
generator into
sound waves.
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A signal generator
produces different
types of signals.

An oscilloscope
shows wave
patterns and allows
us to ‘see’ sound.

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Loudness and amplitude
A sound can be quiet or loud.

quiet sound

loud sound

On an oscilloscope trace, the loudness of a sound is shown
by the height of the wave. This is called the amplitude.
Which word should be crossed out in this sentence?
The larger the amplitude of the wave on the trace,
the louder/quieter the sound.
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Which is the loudest?
Which trace represents the loudest sound?

A

B

Sound A is the loudest.
Sound A has the largest amplitude (i.e. the tallest waves),
so it is the loudest of these two sounds.
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Pitch and frequency
A sound can be high or low – this is the pitch of the sound.

low pitch sound

high pitch sound

On an oscilloscope trace, the pitch of a sound is shown by
how many waves there are. This is called the frequency.
Which word should be crossed out in this sentence?
The greater the number of waves across the oscilloscope
trace, the lower/higher the frequency and pitch.
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Which is the highest?
Which trace represents the sound with the highest pitch?

A

B

Sound B is the highest
pitched.
Sound B has the most number of waves across the
oscilloscope – it has the highest frequency and so
has the highest pitch.
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Wave animation

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Contents

What is sound?
Speed of sound
Reflecting sound
The ear and hearing
Summary activities
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Speed of sound experiment
This investigation to calculate the speed of sound should
be carried out in a quiet open space.

START

STOP
0 0 : 0 0 30 04

100 m
1. When you see the cymbals crash, press START.
2. When you hear the cymbals crash, press STOP.

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Speed of sound experiment – results table
Record the results of the sound experiment.
Experiment distance
(m)

1

100

time
(s)

0.34

speed
(m/s)

294

2
3
4
How are these values used to estimate the speed of sound?

distance
100
=
= 294 m/s
speed =
time
0.34

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Speed of sound experiment – results
The speed of sound in air is about…

340 m/s
Use the results of the cymbals experiment
to calculate the average speed of sound.
How does this calculation for the average speed of sound
compare with the real speed?
What errors could have affected the results of the cymbals
experiment?
Do you think the speed of sound in water is the same
as the speed of in air?
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Sound in different states of matter
Sound needs a substance to travel through and travels by
particles vibrating.
Which state of matter does sound travel fastest through?

solid

liquid

gas

Sound waves travel fastest through solids.
The particles in a solid are closer together than in a gas or
a liquid. This means vibrations are more easily passed
from particle to particle and so sound travels faster.
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Speed of sound in different materials
Sound need particles to travel and the type of substance
affects the speed of sound.
7000

6000

speed of sound (m/s)

6000

5000

5000
4000
3000
2000
1000

1450
330

350

air at 0 C

air at 30 C

0
water

concrete

steel

material
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Breaking the sound barrier!
Which of these travel faster than the speed of sound in air?

distance
(m)

time
(s)

speed
(m/s)

small
aeroplane

600

5

120

jet fighter

900

2

450

cheetah

50

2.5

20

meteorite

10 000

0.35

28,571

The jet fighter and the meteorite travel faster than the speed
of sound in air – this is called breaking the sound barrier.
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Sound or light – which is faster?
During a thunderstorm,
thunder and lightning are
created at the same time.
Which do you notice first?
Usually, you see lightning
before you hear thunder.
Light travels much faster
than sound.
The speed of light is…

300,000,000 m/s

How much faster is light than sound?
How could you use thunder and the speed of sound to
estimate how far away a thunderstorm is?
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Contents

What is sound?
Speed of sound
Reflecting sound
The ear and hearing
Summary activities
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Reflected sound
What happens when a sound wave meets a hard flat
surface?

The sound wave is reflected back from the surface.
This is called an echo.
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Echo experiment
Stand at least 100 m from a large, flat wall with a stop watch.

START

150 m

STOP
1. Use a starting pistol (or clapper board) to make a sound.
2. Measure the time taken between firing the pistol and
hearing the echo.
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Echo experiment
The sound of the starting pistol takes 0.92 s
to travel a distance of 300 m.
How can you use this result to estimate the speed of sound?

distance
speed =
time
=

300
0.92

= 326 m/s
Repeat the experiment several times to obtain an average.
How does your calculation for the average speed of sound
compare with the real value?
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Questions on reflecting sound
1. What is a reflected sound called?
an echo
2. Are hard or soft surfaces best at reflecting sound?
hard surfaces
3. Why are there soft materials on the walls of cinemas
and theatres?

to reduce echoes
4. Name two animals that use echoes for navigation or
communication.

bats and dolphins
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Contents

What is sound?
Speed of sound
Reflecting sound
The ear and hearing
Summary activities
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The ear and sound waves

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How does the ear hear?
1.Sound waves are
collected by the
ear lobe or
pinna.

6.The auditory nerve
takes the signals
to the brain.
6

4

1
2

3

5

2.The waves
travel along
the ear canal.

5.The cochlea
turns these
into electrical
4.The small bones
3.The waves
signals.
(ossicles) amplify
make the ear
the vibrations.
drum vibrate.

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Hearing range
Set the volume and increase the frequency of the signal
provided by the signal generator.

Humans can only hear sounds of certain frequencies.
The range of frequencies a person can hear is called their
hearing range.
What is the hearing range of a healthy young person?

20 Hz to 20,000 Hz
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Comparing hearing ranges
Which animals hear the lowest and the highest frequencies?
100,000
10,000
1,000
frequency
100
(Hz)
10
1
0
human
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dog

bat elephant mouse dolphin
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Hearing ranges and hearing loss
Does everyone have the same hearing range?
We all have slightly different hearing ranges
People lose the ability to hear sounds of high
frequency as they get older.
Almost 1 in 5 people suffer some sort of
hearing loss.
Temporary hearing loss may be caused by ear infections
and colds, after which hearing recovers.
Permanent hearing loss and deafness can be present
at birth or occur if the ear is damaged or diseased.

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Measuring loudness – the decibel scale
decibels

160
aircraft
overhead

personal stereo

140

permanent
ear damage

120
100

loud
bell

80
quiet
countryside

60
40

pin being
dropped

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0

circular saw
at 2m

can just
be heard

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Noise and its effects
A noise is any unwanted sound.
What one person considers noise another person might not.
Can you name any examples?
Noise can cause hearing problems. List three effects of noise.

1. headaches
2. nausea
3. deafness
List three ways of reducing the effects of loud noise.

1. ear protectors
2. double glazing
3. putting noisy machinery in insulated rooms
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Contents

What is sound?
Speed of sound
Reflecting sound
The ear and hearing
Summary activities
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Glossary
amplitude – The height of a wave, which shows how loud
a sound is.

cochlea – The part of the inner ear that changes vibrations

into electrical signals which are then sent to the brain.
decibel – The unit for measuring the loudness of sound (dB).
eardrum – The thin membrane in the ear which vibrates
when sound reaches it.
frequency – The number of waves per second, which
shows the pitch of a sound.
hertz – The unit of frequency (Hz). 1 Hz = 1 wave per second.

oscilloscope – An instrument that shows a picture of sound.
pitch – How high or low a sound is.
sound – A form of energy produced by vibrations, which is
detected by the ears.

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Anagrams

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Multiple-choice quiz

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8 l sound & hearing (boardworks)

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