Download Hearing

11.3 Hearing
11.3 Hearing
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Hearing
Hearing allows us to…
communicate
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Hearing
Hearing allows us to…
enjoy music
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Hearing
Hearing allows us to…
avoid danger
11.3 Hearing
How is sound produced?
Let’s learn about how
sound is produced.
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Producing sound
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rubber band
Experiment
video
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a Does the rubber band produce
any sound?
Yes.
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b What do your hands feel?
The rubber band is vibrating.
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2
Ah~
put fingers
gently on
the throat
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a What do you feel on your throat
when you speak?
There is vibration on my throat.
Ah~
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b What do you feel on your throat
when you stop speaking?
The vibration stops.
Ah~
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tuning fork
rubber
stopper
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3 What do you observe?
The tuning fork produces sound.
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4
plastic basin
with water
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4 What do you observe?
Ripples form on the water surface.
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5 What do the results in steps 1 to 4
show?
They show that sound is produced
by __________________
vibration of objects.
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How is sound produced?
All sound sources, such as musical
instruments, have parts that vibrate.
string
hammer
vibrates
sound
strike the
strings
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From which parts of the instruments
are the musical notes produced?
Write down the vibrating parts of the
musical instruments which produce
sound.
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Hong Kong Chinese Orchestra
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1 Erhu (二胡)
string
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2 Cymbals (鈸)
metal pieces
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3 Drum (鼓)
leather
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4 Suona (嗩吶)
air column
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5 Dizi (笛子)
air column
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6 Zheng (箏)
string
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How is sound produced?
Sound is produced by _________
vibration
of objects.
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How does sound travel?
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11.6
Experiment
video
How sound travels
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large
bowl
plastic
wrap
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11.6
2
rice
grains
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3
strike
gong
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a What happens to the rice grains
on the plastic wrap?
They move/jump up and down.
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b Suggest a reason for the
observation in a.
The vibration of the gong is
transmitted through the air to the
plastic wrap and the rice grains.
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How does sound travel?
When we strike a fork...
vibration of the fork
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How does sound travel?
vibration of
air particles
transmitted
through the air
to our ears
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How does sound travel?
vibration of
air particles
Sound can travel
through air.
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How does sound travel?
Can sound
travel through
solids or liquids?
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11.7
Experiment
video
Can sound travel through solids?
Design a test to find out whether
sound can travel through solids or not.
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1 Write down the apparatus and
materials you need.
A bench in the laboratory
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2 Draw the design of your set-up.
Write down the steps of your test.
1 Form into groups of two Ss.
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2 Draw the design of your set-up.
Write down the steps of your test.
2 Student A taps one end of the
bench. Student B puts his/her ear
against the bench and listens
carefully.
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2
student B
student A
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3 Carry out your test after getting
approval from your teacher.
Write down your observations.
Student B can hear the tapping
sound made by student A.
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4 What can you conclude from
your test?
Sound can travel through wood
(solids).
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11.8
Experiment
video
Can sound travel through liquids?
Design a test to find out whether
sound can travel through liquids or not.
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1 Write down the apparatus and
materials you need.
buzzer
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1000 mL beaker
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small plastic bag
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stethoscope
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water
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2 Draw the design of your set-up.
Write down the steps of your test.
1 Turn on a buzzer. Put it into a
plastic bag and seal the bag.
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2 Draw the design of your set-up.
Write down the steps of your test.
2 Put the bag into a beaker of
water.
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2 Draw the design of your set-up.
Write down the steps of your test.
3 Put the chestpiece of the
stethoscope into the water and
listen through the earpiece.
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2
stethoscope
buzzer
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3 Carry out your test after getting
approval from your teacher.
Write down your observations.
I can hear the sound produced by
the buzzer.
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4 What can you conclude from
your test?
Sound can travel through water
(liquids).
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How does sound travel?
Can sound
travel through
a vacuum?
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11.9
Experiment
video
Can sound travel through a vacuum?
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to power
supply
electric bell
bell jar
hammer
to vacuum pump
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2 Switch on the electric bell.
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2 Can you hear the bell ringing?
Yes.
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3 Turn on the vacuum pump to
remove air from the bell jar.
turn on the
vacuum pump
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a What happens to the sound of
the bell?
turn on the
vacuum pump
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a It fades while air is being pumped
out. No sound can be heard
eventually.
turn on the
vacuum pump
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b Is the hammer of the bell still
hitting the bell?
Yes.
turn on the
vacuum pump
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4 Turn off the vacuum pump and let
air enter the bell jar.
turn off the
vacuum pump
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4 Can you hear the bell ringing?
Yes.
turn off the
vacuum pump
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5 What can you conclude from your
observations?
Sound cannot travel through
a vacuum.
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How does sound travel?
Sound needs a
medium (介質)
to travel.
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How does sound travel?
Sound travels at different speeds in
different media.
in solids >
fastest
in liquids >
in gases
slowest
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How does sound travel?
No sound.
Why?
vacuum
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How does sound travel?
Sound cannot
travel through
a vacuum
vacuum
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How does sound travel?
No particle for
transmitting
vibrations
vacuum
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How does sound travel?
In space
communicate
through a
radio system
vacuum
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How does sound travel?
Sound needs a medium to travel.
The medium can be gases,
liquids or solids.
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vibration
1 Sound is produced by _________
of objects.
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2 Sound must travel through a
medium which can be
_________,
solids
liquids or
_________,
_________
gases
_________.
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3 Sound cannot travel through a
vacuum
_________.
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The structure of our ear
3D model
The ear can be divided into:
outer ear middle ear inner ear
(外耳)
(中耳)
(內耳)
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Examining the ear model
human ear model
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outer
ear
middle
ear
a pinna
b ear canal
c eardrum
inner
ear
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outer
ear
middle
ear
inner
ear
d ear bones
e cochlea
f auditory nerve
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How do we hear?
1 Sound in the surroundings is
collected by the pinna.
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3D animation
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How do we hear?
2 The sound travels along the
ear canal and hits the eardrum.
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How do we hear?
3 The sound causes the eardrum to
vibrate.
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How do we hear?
4 The vibrations are magnified by
the ear bones and passed to the
inner ear.
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How do we hear?
5 The vibrations stimulate the
receptors in the cochlea to send
out messages.
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How do we hear?
6 The messages are sent to the
brain along the auditory nerve
for interpretation.
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The limitations of our ears
I can’t hear the whistle. Why?
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The limitations of our ears
We can only hear sounds within a
certain range of frequencies (頻率).
• number of vibrations
per second
• unit: hertz (Hz)
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The limitations of our ears
We can only hear sounds within a
certain range of frequencies (頻率).
the faster an object vibrates
the higher the frequency of
the sound it produces
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Experiment
video
What is our hearing range?
signal generator
loudspeaker
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Turn it on
signal generator
loudspeaker
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1 Start with the lowest frequency and
then slowly increase the frequency.
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2 Raise your hand as soon as you
hear the sound.
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2 Record the frequency. This is the
lower limit of your hearing.
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a The lowest frequency that I can
hear is _____ Hz.
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b The lowest frequency that
everyone in the class can hear
is _____ Hz.
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3 Continue to increase the frequency
of the sound.
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3 Raise your hand again when you
can no longer hear the sound.
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3 Record the frequency. This is the
upper limit of your hearing.
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a The highest frequency that I can
hear is _____ Hz.
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b The highest frequency that
everyone in the class can hear
is _____ Hz.
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c The range of frequencies that the
class can hear is _____ Hz to
_____ Hz.
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The limitations of our ears
Audible frequency range
(聽頻範圍) of humans:
~20 Hz to 20 000 Hz
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The limitations of our ears
Humans can only hear sounds
within a certain range of
frequencies.
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Audible frequency ranges of other
animals
goldfish
human
dog
dolphin
bat
Sound
frequency (Hz)
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Audible frequency ranges of other
animals
frequency of dog
whistle: 22 000 Hz
Sound
frequency (Hz)
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Audible frequency ranges of other
animals
sharp enough to
draw dog’s attention
Sound
frequency (Hz)
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Audible frequency ranges of other
animals
too high for humans
to hear
Sound
frequency (Hz)
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Noise pollution
What is noise
(噪音)?
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What is noise?
Noise
sound that is
unwanted, disturbing,
or can cause harm to
our ears
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What is noise?
Sources of noise:
machinery
transportation
construction works
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What is noise?
loudness (音量) of sound /
sound level
measured in
decibels (dB) (分貝)
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Sound levels of some
sounds in daily life
high
decibel
level
mid
decibel
level
low
decibel
level
Sound level (dB)
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What is noise?
decibel meter
(分貝計)
used to measure
sound levels
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11.6
Measuring sound levels at school
Use a decibel meter to measure the
sound levels in…
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11.6
Environment
1 Classroom with air
conditioning on and
windows closed
2 Classroom with air
conditioning off and
windows open
Sound level (dB)
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Environment
3 Playground during
recess
4 The street near the
front door of the
school
Sound level (dB)
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Which environment is the noisiest?
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How does noise affect us?
Noise pollution
(噪音污染)
 may disturb
sleep
 cause mental
stress
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How does noise affect us?
Noise pollution
(噪音污染)
 may damage our ears, lead to
hearing loss or even deafness
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11.7
Take care of our ears when using
portable MP3 players
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11.7
1 Why do some people turn their MP3
players to very high volume levels?
They want to cover the noise on
busy roads or on the MTR.
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2 Besides causing damage to the
ears, suggest some other potential
dangers of using portable MP3
players on the street.
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2 The users may not be alert to the
traffic conditions on the road.
Accidents may result.
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3 What should we do to protect our
ears when enjoying music using
portable MP3 players?
Keep the music volume low.
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Protecting our ears
If we stay in a
noisy environment
for a long time …
Bomb!
Beep~
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Protecting our ears
permanent
losswill
receptors
andhearing
nerve cells
may result
be permanently
damaged
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Protecting our ears
How can we
protect our ears?
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Protecting our ears
a Stay away from
noisy places.
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Protecting our ears
b Wear ear protectors when working
in a noisy environment.
ear protector
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Protecting our ears
c When listening to music, keep the
volume level low.
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Protecting our ears
d Do not pick our ears with hard
objects.
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Noise control
Some measures taken by the
Hong Kong government…
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Noise control
a Build noise barriers
(隔音屏障) along
busy roads and
railways.
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Noise control
b Limit the time for noisy construction
works to daytime on weekdays.
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Noise control
c Impose penalties on people who
disturb neighbours by making noise
during particular periods of time.
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Noise pollution
Long term exposure to noise or
loud sound may cause mental
stress and hearing loss.
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Noise pollution
We should protect our ears
from noise.
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sound in the collected by
surroundings
a pinna
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the sound
travels along
a pinna
b ear canal
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the sound causes
vibrations in
b ear canal
c eardrum
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transmits
vibrations to
c eardrum
d ear bones
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magnify
vibrations,
transmit to
d ear bones
e cochlea
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sends out
messages
that travel
along
e cochlea
f auditory nerve
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carries
messages to
f auditory nerve
g brain
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interprets the
messages as
g brain
sound