8 l sound & hearing (boardworks)
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Transcript of 8 l sound & hearing (boardworks)
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20051 of 36
KS3 Physics
8L Sound and Hearing
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20052 of 36
8L Sound and Hearing
Contents
What is sound?
Speed of sound
The ear and hearing
Summary activities
Reflecting sound
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What causes sound?
The tuning fork vibrates and you hear a sound.
Sounds are made when an object vibrates.
Take a tuning fork and strike it against a block of wood.
What do you observe?
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Good vibrations!
What vibrates so that the following make sounds?
violin strings
voice box
loudspeaker cone
drum skin
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Remove the air from the bell jar and what happens to the sound?
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.
The sound cannot be heard because there is no air inside the bell jar (a vacuum).
vacuum pump on
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Sound waves can be studied with this type of equipment.
signal generator
oscilloscopeloudspeaker
Studying sound waves
A signal generator produces different types of signals.
A loudspeaker converts signals from the signal generator into sound waves.
An oscilloscope shows wave patterns and allows us to ‘see’ sound.
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The larger the amplitude of the wave on the trace, the louder/quieter the sound.
Loudness and amplitude
A sound can be quiet or loud.
loud soundquiet soundOn 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?
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Which is the loudest?
Sound A is the loudest.
Which trace represents the loudest sound?
Sound A has the largest amplitude (i.e. the tallest waves), so it is the loudest of these two sounds.
A B
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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 soundOn 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?
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.
BA
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Wave animation
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8L Sound and Hearing
Contents
What is sound?
Speed of sound
The ear and hearing
Summary activities
Reflecting sound
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100 m
00:0000
START
00:0034
STOP
1. When you see the cymbals crash, press START.
2. When you hear the cymbals crash, press STOP.
This investigation to calculate the speed of sound should be carried out in a quiet open space.
Speed of sound experiment
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Experiment
distance (m)
time(s)
speed(m/s)
1
2
3
4
Record the results of the sound experiment.
=294 m/s distance
timespeed = =
100
0.34
100 0.34 294
Speed of sound experiment – results table
How are these values used to estimate the speed of sound?
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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?
The speed of sound in air is about…
What errors could have affected the results of the cymbals experiment?
340 m/s
Do you think the speed of sound in water is the same as the speed of in air?
Speed of sound experiment – results
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Sound in different states of matter
Sound needs a substance to travel through and travels by particles vibrating.
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.
gassolid liquid
Sound waves travel fastest through solids.
Which state of matter does sound travel fastest through?
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Sound need particles to travel and the type of substance affects the speed of sound.
330 350
1450
5000
6000
0
1000
2000
3000
4000
5000
6000
7000
air at 0 C air at 30 C water concrete steel
material
sp
eed
of
so
un
d (
m/s
)
Speed of sound in different materials
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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
28,571
20
Breaking the sound barrier!
The jet fighter and the meteorite travel faster than the speedof sound in air – this is called breaking the sound barrier.
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Usually, you see lightning before you hear thunder. Light travels much faster than sound.
The speed of light is…
During a thunderstorm, thunder and lightning are created at the same time.
Which do you notice first?
How could you use thunder and the speed of sound to estimate how far away a thunderstorm is?
300,000,000 m/s
How much faster is light than sound?
Sound or light – which is faster?
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8L Sound and Hearing
Contents
What is sound?
Speed of sound
The ear and hearing
Summary activities
Reflecting sound
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The sound wave is reflected back from the surface.
This is called an echo.
What happens when a sound wave meets a hard flat surface?
Reflected sound
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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.
START
150 m
Stand at least 100 m from a large, flat wall with a stop watch.
STOP
Echo experiment
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How can you use this result to estimate the speed of sound?
The sound of the starting pistol takes 0.92 s to travel a distance of 300 m.
=326 m/s
distance
timespeed =
=300
0.92
Repeat the experiment several times to obtain an average.
Echo experiment
How does your calculation for the average speed of sound compare with the real value?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?
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
hard surfaces
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8L Sound and Hearing
Contents
What is sound?
Speed of sound
The ear and hearing
Summary activities
Reflecting sound
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The ear and sound waves
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1.Sound waves are collected by the ear lobe or pinna.
2.The waves travel along the ear canal.
3.The waves make the ear drum vibrate.
4.The small bones (ossicles) amplify the vibrations.
5.The cochlea turns these into electrical signals.
6.The auditory nerve takes the signals
to the brain.
3
4
5
6
1
2
How does the ear hear?
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Set the volume and increase the frequency of the signal provided by the signal generator.
20 Hz to 20,000 Hz
Humans can only hear sounds of certain frequencies.
What is the hearing range of a healthy young person?
The range of frequencies a person can hear is called their hearing range.
Hearing range
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100,000
10,000
1,000
100
10
1
0
human dog elephantbat mouse dolphin
Which animals hear the lowest and the highest frequencies?
frequency(Hz)
Comparing hearing ranges
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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.
Does everyone have the same hearing range?
Hearing ranges and hearing loss
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160
140
120
100
80
60
40
20
0
permanent ear damage
can just be heard
aircraft overhead
decibels
circular saw at 2m
quiet countryside
pin being dropped
loud bell
personal stereo
Measuring loudness – the decibel scale
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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.
2. nausea
1. headaches
3. deafness
List three ways of reducing the effects of loud noise.
1. ear protectors
3. putting noisy machinery in insulated rooms
2. double glazing
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8L Sound and Hearing
Contents
What is sound?
Speed of sound
The ear and hearing
Summary activities
Reflecting sound
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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