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Sound
Sound
Sound
Sound
Sound
Sound
What is sound?
• Sound is a form of energy.
• It is made when an object or
material vibrates.
• A vibration is a fast, backwards
and forwards movement that
repeats many times.
• A sound wave is produced when
air molecules are alternately
squashed together and pulled
apart.
What is sound?
compression (squashing)
rarefaction (spreading out)
Slinky or long spring
energy moves this way
particles vibrate this way
Sound is a longitudinal
wave, like the wave shown
on this slinky. The molecules
vibrate in the same direction
that the energy of the wave
travels in.
Making Sounds
A sound is made when an object or material VIBRATES.
Take, for example, a guitar:
To make a sound with a guitar a string has to
vibrate. We can raise the pitch of the sound a
guitar makes by doing three things:
1) _________ the length of the string
2) _________ the string
3) Using a _________ string
We can make the sound louder by ________ the string harder
Words – tightening, thinner, increasing, plucking
Making Sounds
A sound is made when an object or material VIBRATES.
Take, for example, a guitar.
To make a sound with a guitar a string has to
vibrate. We can raise the pitch of the sound a
guitar makes by doing three things:
1) _________
increasing the length of the string
tightening the string
2) _________
3) Using a _________
thinner string
We can make the sound louder by ________
plucking the string harder
Words – tightening, thinner, increasing, plucking
Frequency and pitch
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.
Frequency and pitch
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.
Frequency and pitch
• Frequency = the number of sound
vibrations set up in 1 second and is
measured in Hertz (Hz).
• Pitch = how high or low the sound
is (depends on how rapidly the
‘sound producer’ vibrates).
Frequency and pitch
• When you pluck the top string of a guitar, it
vibrates 660 times in 1 second. What is the
frequency of the sound it makes?
• Answer = 660Hz
• When you pluck the bottom string, it vibrates only
165 times each second. What is the frequency of
the sound it makes?
• Answer = 165Hz
• What is the connection between frequency of a
sound and its’ pitch?
• Answer: The top string makes a higher pitched
sound than the bottom one. Therefore the higher
frequency of a sound, the higher is its’ pitch.
Frequency and pitch
• When you pluck the top string of a guitar, it
vibrates 660 times in 1 second. What is the
frequency of the sound it makes?
• Answer = 660Hz
• When you pluck the bottom string, it vibrates only
165 times each second. What is the frequency of
the sound it makes?
• Answer = 165Hz
• What is the connection between frequency of a
sound and its’ pitch?
• Answer: The top string makes a higher pitched
sound than the bottom one. Therefore the higher
frequency of a sound, the higher is its’ pitch.
Amplitude
• Sounds can vary in ‘loudness’.
• A loud sound has more energy than a
quiet sound.
• The loudness of a sound is its’
amplitude.
• Large vibrations cause a loud (high
amplitude) sound.
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.
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.
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.
A signal generator
produces different
types of signals.
An oscilloscope
shows wave
patterns and allows
us to ‘see’ sound.
Using an oscilloscope
An oscilloscope can be used to compare the
amplitude and frequency of different sound waves.
Using an oscilloscope
1) Quiet sound, low frequency:
2) Quiet sound, high frequency:
3) Loud sound, low frequency:
4) Loud sound, high frequency:
How does sound travel?
• Sound travels as a series of
vibrations through a material.
• In 1705, Francis Hawksbee showed
a famous experiment first
performed by Robert Boyle in 1660
– the bell in a jar experiment.
• A pump was used to remove all of
the air from the bell jar to form a
vacuum.
Robert Boyle
How does sound travel?
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- it is a vacuum.
How does sound travel?
As we know, sound waves are formed when something vibrates.
But how does the sound reach our ears?
Air molecules
1) An object
makes a
sound by
vibrating
2) The vibrations pass
through air by making air
molecules vibrate
3) These
vibrations are
picked up by
the ear
How does sound travel?
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.
How does sound travel?
• A vacuum is an empty space that contain
no particles at all.
• Sound cannot travel through a vacuum
because there are no particles to vibrate
and carry the sound wave.
How does sound travel?
• What is a vacuum?
• The Sun is an exploding ball of hot gases
with a surface temperature of 5500C. Space
is a vacuum. Why can we see the Sun but not
hear the sound it makes?
• Astronauts sometimes leave their spacecraft
to repair a faulty satellite. Why do they use a
radio system to talk to each other?
The speed of sound
• The speed of sound can be calculated using
the following equation:Speed of sound = distance between 2 people
÷ time taken for sound to travel this distance
Speed of sound
The speed of sound in air is around 330 m/s. What happens
when sound travels through different materials?
5000
4500
4000
Speed of
sound
(in m/s)
3500
3000
2500
2000
1500
1000
500
0
Air
Water
Brick
Iron
Material
Conclusion
The denser the material, the faster sound travels through it
Speed of sound in different materials
Sound need particles to travel and the type of substance
affects the speed of sound.
7000
6000
6000
5000
5000
4000
3000
2000
1450
1000
330
350
air at 0 C
air at 30 C
0
water
material
material
concrete
steel
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.
How does the ear work?
Inner ear bones - the vibrating
ear drum makes the inner ear
bones move like levers
))))
Auditory nerve - carries
electrical messages to the
brain
Sound Waves air vibrates and
moves towards the
ear
Ear drum - the vibrating air
causes the ear drum to vibrate
Cochlea - the bones
movement is
transferred to fluid
which moves hairs
How does the ear work?
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
dog
bat
elephant mouse dolphin
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.
Measuring loudness – decibel scale
decibels
160
Aircraft
overhead
Circular
saw at 2m
140
Personal stereo
PERMANENT
EAR DAMAGE
120
100
Loud bell
80
60
40
Pin being
dropped
20
0
Quiet
countryside
Can just be
heard
Ultrasound
Ultrasound ( high frequency sound) is the region of sound
above 20,000Hz – it cannot be heard by humans. There
are a number of uses for ultrasound:
•
•
•
•
Pre-natal screening to check the
development of unborn babies
Cleaning delicate objects or
machinery that cannot be
dismantled.
Checking for cracks in metal
structures e.g. aircraft.
Medical treatment e.g. kidney
stones, sports injuries.
How does ultrasound work?
Ultrasonic waves are partly _________ at the boundary as
they pass from one _______ to another. The time taken for
these reflections can be used to measure the _______ of the
reflecting surface and this information is used to build up a
__________ of the object.
Words – depth, reflected, picture, medium
How does ultrasound work?
Ultrasonic waves are partly _________
reflected at the boundary as
they pass from one medium
_______ to another. The time taken for
these reflections can be used to measure the _______
depth of the
reflecting surface and this information is used to build up a
picture of the object.
__________
Words – depth, reflected, picture, medium
Other uses for sound
• Sonar, using sound
waves, is used to
measure the depth of
water.
• Echoes of sound waves
are also used to detect
places where oil
deposits might be found.