Download Sound and Hearing

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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.
Sound travels because the vibrating
object makes nearby particles vibrate.
Sound needs a medium to travel through
– it cannot pass through a vacuum.
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Good vibrations!
What vibrates so that each of these objects makes sound?
drum skin
harp strings
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mouth blowing
horn
lute strings
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How does sound travel through the air?
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‘Seeing’ sound waves
speaker
oscilloscope
If we connect an mp3 player to a speaker, we can all
hear the sound produced.
If we also connect an oscilloscope to the mp3 player then
we can ‘see’ the sound waves.
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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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Pitch and frequency
A sound can be high or low – this is the pitch of the sound.
low pitch
high pitch
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 frequency of the waves
on the trace, the lower/higher the pitch.
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Which wave is the loudest and highest?
Which trace represents the loudest sound?
A
B
Sound A has the largest
amplitude (i.e. the tallest
waves), so it is the loudest
of these two sounds.
Which trace represents the sound with the highest pitch?
A
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B
Sound B has the greater
number of waves across
the oscilloscope – it has
the highest frequency and
so has the highest pitch.
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Amplitude and wavelength
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Describing sound waves
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Sound waves summary
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Speed of sound – experiment
This investigation for calculating the speed of sound should
be carried out in a quiet open space.
One student should hold a stopwatch, whilst another should
be holding some cymbals 100 metres away.
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 – results
Record the results of the sound experiment in a table like this:
Experiment
Distance (m)
Time (s)
Speed (m/s)
1
100
0.34
294
2
3
4
How are these values used to estimate the speed of sound?
distance
speed
=
=
time
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100
=
294 m/s
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Speed of sound – analysis
The first cymbal experiment gives an estimate for the
speed of sound as 294 m/s.
Use the average of your results to calculate another
estimate for the speed of sound.
1. How does this calculation for the
average speed of sound compare
with the real speed?
2. What errors could have affected the
results of the cymbals experiment?
3. Do you think the speed of sound in
water is the same as the speed of
sound in air?
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Energy transfer
How many different energy transfers do you think take place
during this experiment?
When the cymbals crash there is a transfer of kinetic energy
from the cymbals to the air particles.
When the sound waves reach the ear, there is a transfer of
kinetic energy from the air particles to the eardrum.
kinetic energy
of cymbals
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kinetic energy
of air particles
kinetic energy
in eardrum
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Sound in different materials
Sound needs a substance through which to travel because it
travels by making particles vibrate.
Which state of matter does sound travel fastest through?
Sound waves travel fastest through solids.
The particles in a solid are closer together than in a gas,
and more tightly bound than in a liquid. This means
vibrations are more easily passed from particle to particle,
and so sound travels faster.
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Sound waves in different materials
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Speed of sound in different materials
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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
10,000
0.35
28,571.4
meteorite
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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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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Investigating echoes
Plan an investigation to measure the speed of sound using
echoes.
You may use any of the following equipment:
stopwatch
clapper board
starting pistol
hard, flat surface
Remember to make sure it is a fair test.
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Analysing your results
Calculate the speed of sound for each of your distances
using the formula below.
distance
speed
=
time
1. How do your calculations compare with the actual speed
of sound in air?
2. Which of your distances gave the most accurate answer?
3. Were there any errors in your experiment?
4. Could you improve the experiment in any way to make it
even more accurate?
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How do we hear?
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How does the ear work?
1. Sound waves
are collected
by the outer
ear (or
pinna).
6.The auditory nerve
takes the signals
to the brain.
2. The waves
travel along
the ear canal.
3. The waves reach
the eardrum and
make it vibrate.
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5. The cochlea
4. The small bones
turns these
(ossicles) amplify
into electrical
the vibrations.
signals.
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The ear and hearing summary
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What range of frequencies can you hear?
Humans can only hear sounds of certain frequencies.
The range of frequencies a person can hear is called
their hearing range.
Hearing range can be tested using a pitch sweep, in which
the frequency of a sound wave is gradually increased.
This can be created using a signal generator and loudspeaker.
What is the hearing range of a healthy young person?
20 Hz to 20,000 Hz
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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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Hearing ranges
As we get older, our ability to hear high pitched sounds
deteriorates. Some shopkeepers use this to their advantage.
A device has been developed called a ‘Mosquito’ which
emits sounds of around 20,000 Hz.
This is audible, and potentially
quite annoying, for teenagers
who may be loitering around
the shop, but is not noticeable
to older customers.
Some human rights groups have claimed that the devices
demonise young people indiscriminately. Others claim they
are a cheap, non-violent way to deal with troublesome yobs.
What do you think?
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Should ‘Mosquitoes’ be banned?
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Animals’ hearing ranges
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Ordering volumes
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Reducing noise
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Glossary
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Anagrams
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Multiple-choice quiz
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