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KS4 Waves : Sound
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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.
All sounds are caused by vibrations.
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Music
What vibrates when you sing?
Your voice-box.
What vibrates when you play a violin?
The strings
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The Bell-jar experiment
What happens when the air is removed from the bell-jar?
Sound waves are vibrations and so need a substance to
travel through.
With air inside, the sound can be heard.
With nothing inside [a vacuum], the
sound can’t be heard.
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Sound : How fast does it travel?
You need a quiet open space at least 100m long to
perform this investigation.
STOP
START
00:0000
34
> 100m
1) When you see the cymbals crash, press START.
2) When you hear the cymbals crash, press STOP.
 Write your results in a table like this:
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Sound : How fast does it travel?
Try
Distance
[m]
Time
[s]
Speed
[m/s]
1.
100
0.34
294
2.
3.
4.
 Calculate your average speed of sound :
Av. = [try 1 + try 2 + try 3 + try 4]  4.
 What errors could have crept into your results?
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Sound : What does it need to travel?
 Sound waves need particles in order to travel.
 The substance that the sound travels through affects the
speed of sound greatly.
7000
6000
6000
5000
5000
4000
3000
2000
1450
1000
330
350
Air at 0 C
Air at 30 C
0
W ater
Concrete
Steel
Material
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Travelling sound
Sound
travels
particles
vibrating.
Which
statebydoes
sound
travel fastest through?
To understand this betterWhy?
you need to remember what
the particles look like in a solid, liquid and a gas:
solid
liquid
gas
In whichtravels
Sound
state are
fastest
the through
particlessolids
closest
because
together?
the particles
are closer together than in a liquid and a gas,solid
so the
vibrations
are more
easily
passed
from apart?
particle to particle.
In which state
are the
particles
furthest
gas
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Sound : How fast does it travel?
Most of us have seen thunder
storms - which comes first, the
thunder or lightning?
The lightning gets to our eyes
before the thunder reaches our
ears.
1) Thunder & lightning are made at the same time so we
deduce that light travels much faster than sound.
2) In fact light travels so fast that:
the time between seeing the flash and hearing the bang
= time taken for sound to travel.
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Reflection : Echoes
You should remember that sound is produced by a
vibration and travels as a longitudinal wave
………..and that sound travels at different speeds through
different substances [or media]
Sound waves reflect off hard, smooth
surfaces to produce echoes.
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Using echoes
What do we call reflected sound?
An echo
Which surfaces are the best at reflecting sound:
HARD or SOFT ?
How are echoes reduced in cinemas and theatres?
By using soft materials on the walls such as curtains.
Name two animals that use echoes?
Bats and dolphins
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Reflection : Echoes
 Stand at least 100m
from a large, straight
wall.
150m
 Measure the distance
from you to the wall.
 Use a starting pistol
[or clapper board] to
make a sound.
 Measure the time taken
START
STOP
between firing the pistol
and hearing the echo.
Remember, this is
‘two way travel time’ [twtt]
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Reflection : Echoes
The sound takes 0.92s to travel 300m.
Remember the formula for speed?
SPEED = DISTANCE  TIME
v
=
300
 0.92
v
=
326 m/s
Repeat this several times to obtain an average.
For the Higher Tier paper you will need to be able to
change the subject of the formula.
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Reflection : Questions
Distance
[m]
Time
[s]
Speed
[m/s]
Small
aeroplane
600
5
120

Jet fighter
900
2
450

Meteorite
10,000
0.35
28571
Cheetah
50
2.5
20
Which of these travel faster than the speed of sound in air?
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Studying sound
Loudspeakers convert
the signal from the
signal generator into
sound waves.
The oscilloscope
allows us to study
the frequency and
loudness of a sound.
Signal generators can
produce signals over a
range of frequencies and
of varying amplitudes.
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Pitch (or frequency)
A high pitch sound
A low pitch sound.
The shorter/longer the wavelength of the wave on the
trace; the lower/higher the frequency of the sound.
The more waves you can see, the higher the pitch/frequency.
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Oscilloscope traces
Which trace represents the highest pitched sound?
A
B
‘A’ is the highest pitched sound because it has the shortest
wavelength/most number of waves visible.
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Loudness
A quiet sound
A loud sound
The larger/smaller the amplitude of the wave on the
trace; the louder/quieter the sound.
The bigger the waves you can see, the louder the sound.
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Oscilloscope traces
Which trace represents the loudest sound?
A.
B.
‘B’ is the loudest sound because it has the largest amplitude, the
larger the amplitude the more energy a wave has, the more
energy it has, the louder the sound.
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Wave animation
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Sound : What can I hear?
Increase the frequency of the signal provided by a signal
generator whilst keeping the volume the same.
20 Hz
The lowest frequency I can hear is ________
20 000 Hz
The highest frequency I can hear is ________
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Sound : Are we all the same?
You have just found your hearing range - could everyone
hear exactly the same frequencies as you?
We all have slightly different hearing ranges but almost 1
in 5 people suffer some sort of hearing loss.
Temporary hearing loss may be caused by ear infections
and colds and 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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Sound : Are we all the same?
Hearing is tested using an audiometer and the results
are shown on an audiogram.
80
70
Hearing Loss [dB]
60
50
optimal
hearing
40
impaired
hearing
30
20
10
0
0
2000
4000
6000
8000
Frequency of sound [Hz]
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Sound : Hearing Ranges
Hearing Ranges of Animals
bats
pigeons
humans
mice
elephants
moths
1,000,000
100,000
10,000
1,000
100
10
1
0
Which animal can
hear the lowest
highest
frequency?
Frequency [Hz]
pigeons
moths
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Sound : The ear
1. Sound
waves are
collected
by the ear
lobe or
pinna.
3. The waves
2. The waves
travel along the make the ear
drum vibrate.
ear canal.
6. The
auditory
nerve
takes the
signals to
the brain.
4. The
small bones
[ossicles]
amplify the
vibrations.
5. The
cochlea turns
the vibrations
into electrical
signals.
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Sound : How loud are sounds?
Aircraft overhead 150
140
120
Personal stereo
Permanent
ear damage
Loud bell
100
A circular saw at 2m
80
60
40
Quiet countryside
20
Pin being dropped
10
0
Can just be heard
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What is noise?
A noise is any unwanted sound.
What are the effects of noise?
1.
Deafness
_________
2.
Vomiting
_________
3.
Headaches
_________
4.
Nausea
_________
What you might not
consider noise, loud
music for example,
other people might!
How can you reduce the
effects of loud noise?
Ear protectors
1._________________
Double glazing
2._________________
Putting noisy machinery
3.____________________
in insulated rooms
_____________________
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Using Sound Waves : Ultrasound
Our ears can’t detect frequencies above 20 kHz.
Sound above 20 kHz is called ULTRASOUND.
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Using Sound Waves : Ultrasound
Ultrasound has many uses, especially in medicine where it
is used to scan the fetus.
10 weeks
20 weeks
Why
doare
doctors
ultrasound
to scan the and
foetus
X rays
more use
energetic
and penetrating
areand
a lotnot
more
X
rays whichthey
givecould
a clearer
picture?
dangerous,
cause
damage to the growing baby.
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Using Sound Waves : Ultrasound
Use the internet or research books to find out about other
uses of ultrasound.
These search terms should help:
bats
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How ultrasound is used?
Ultrasound like all sound is
reflected different amounts by
different materials.
A receiver can be used to detect
the amount of ultrasound reflected
or lost from a signal.
A computer can then be used to
build up an image of these
ultrasound signals.
This is how ultrasound is used in
prenatal scanning and industrial
quality control.
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What is the upper range of human hearing?
A. 20 Hz
B. 200 Hz
C. 2 000 Hz
D. 20 000 Hz

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What causes all sounds?
A. Vibrations

B. Reflections
C. Refractions
D. Heat
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Which of the following can sound not
travel through?
A. Liquid
B. Vacuum

C. Solid
D. Gas
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A ship releases an echo sounding and 4
seconds later receives a signal from the
seabed, how deep is the sea?
(speed of sound in water is 1500 m/s)
A. 6000m
B. 375m
C. 750m
D. 3000m

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Which of the following is not a use
of ultrasound?
A. Prenatal scanning
B. Quality control in industry
C. Cleaning delicate machinery
D. Cooking food

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