1. KS3 Physics
8L Sound and Hearing

2. Sounds are made when an object vibrates.
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.

3. Good vibrations!
What vibrates so that each of these objects makes sound?
violin strings
drum skin
voice box
loudspeaker cone

4. 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).

5. 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.
An oscilloscope shows wave patterns and allows us to ‘see’ sound.
A signal generator produces different types of signals.

6. 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.

7. Which is the loudest? A B Sound A 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.

8. low pitch sound high pitch sound
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.

9. Sound B has the highest pitch.
Which is the highest?
Which trace represents the sound with the highest pitch? A B
Sound B has the highest pitch.
Sound B has the most number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch.

10. Speed of sound experiment
This investigation to calculate the speed of sound should be carried out in a quiet open space.
START
STOP
100 m
1. When you see the cymbals crash, press START.
2. When you hear the cymbals crash, press STOP.

11. Speed of sound experiment – results table
Record the results of the sound experiment in a table like this:
Experiment
distance (m)
time
(s)
speed
(m/s) 1 2 3 4
100
0.34
294
How are these values used to estimate the speed of sound?
distance
time
speed = =
100
0.34 =
294 m/s

12. 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 sound in air?

13. 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.

14. 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
jet fighter
900 2
cheetah 50
2.5
meteorite
10 000
0.35
120
450 20
28 571
The jet fighter and the meteorite travel faster than the speed
of sound in air – this is called breaking the sound barrier.

15. 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.
300,000,000 m/s
The speed of light is…
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?

16. 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.

17. Echo experiment START STOP
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.

18. Echo experiment distance time speed = = 300 0.92 = 326 m/s
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
time
speed = =
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?

19. 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

20. 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
5.The cochlea turns these into electrical signals.
2.The waves travel along the ear canal.
3.The waves reach the eardrum and make it vibrate.
4.The small bones (ossicles) amplify the vibrations.

21. 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

22. 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.

23. Measuring loudness – the decibel scale
personal stereo
aircraft
overhead
160
140
120
100 80 60 40 20
loud bell
quiet
countryside
circular saw
at 2m
can just be heard
pin being
dropped

24. 3. putting noisy machinery in insulated rooms
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

25. amplitude – The height of a wave, which shows how loud
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.