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11.3 Hearing 1
Hearing11.11.33
11.3 Hearing 2
HearingHearing allows us to…
communicate
11.3 Hearing 3
HearingHearing allows us to…
enjoy music
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HearingHearing allows us to…
avoid danger
11.3 Hearing 5
How is sound produced?
Let’s learn about how sound is produced.
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Experiment video
Producing sound11.5
1rubber band
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11.5
1
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11.5
a Does the rubber band produce any sound?
Yes.
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11.5
b What do your hands feel?
The rubber band is vibrating.
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11.5
2Ah~
put fingers gently on the throat
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11.5
a What do you feel on your throat when you speak?
There is vibration on my throat.
Ah~
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11.5
b What do you feel on your throat when you stop speaking?
The vibration stops.
Ah~
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3
rubber stopper
tuning fork
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3
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11.5
What do you observe?
The tuning fork produces sound.
3
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11.5
4
plastic basin with water
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11.5
What do you observe?
Ripples form on the water surface.
4
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11.5
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.
hammerstring
strike the strings
vibrates
sound
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11.5From 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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11.5Hong Kong Chinese Orchestra
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11.5
1 Erhu (二胡 )
string
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11.5
metal pieces
2 Cymbals ( 鈸 )
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11.5
leather
3 Drum ( 鼓 )
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11.5
4 Suona (嗩吶 )
air column
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11.5
air column
5 Dizi (笛子 )
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11.5
string
6 Zheng ( 箏 )
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Sound is produced by _________ of objects.
How is sound produced?
vibration
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How does sound travel?
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Experiment video
How sound travels11.6
1
plastic wraplarge
bowl
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2
rice grains
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11.6
3
gong
strike
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11.6
a What happens to the rice grains on the plastic wrap?
They move/jump up and down.
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11.6
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?
Sound can travel through air.
vibration of air particles
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How does sound travel?
Can sound travel through solids or liquids?
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Experiment video
Can sound travel through solids?11.7
Design a test to find out whether sound can travel through solids or not.
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11.7
1 Write down the apparatus and materials you need.
A bench in the laboratory
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11.7
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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11.7
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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11.7
2 student A
student B
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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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Experiment video
Can sound travel through liquids?11.8
Design a test to find out whether sound can travel through liquids or not.
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11.8
1 Write down the apparatus and materials you need.
buzzer 1
1000 mL beaker 1
small plastic bag 1
stethoscope 1
water
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11.8
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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11.8
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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11.8
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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11.8
2
buzzer
stethoscope
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11.8
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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11.8
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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Experiment video
Can sound travel through a vacuum?11.9
1 to power supply
hammer
bell jar
electric bell
to vacuum pump
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11.9
2 Switch on the electric bell.
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11.9
Can you hear the bell ringing?
Yes.
2
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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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11.9 a What happens to the sound of
the bell?
turn on the vacuum pump
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11.9 a
turn on the vacuum pump
It fades while air is being pumped out. No sound can be heard eventually.
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11.9
b Is the hammer of the bell still hitting the bell?
Yes.
turn on the vacuum pump
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11.9
4 Turn off the vacuum pump and let air enter the bell jar.
turn off the vacuum pump
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11.9
Can you hear the bell ringing?
Yes.
4
turn off the vacuum pump
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11.9
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 in liquids
slowest
in gases
fastest
> >
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How does sound travel?
vacuum
No sound. Why?
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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 vacuum
communicate through a radio system
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Sound needs a medium to travel. The medium can be gases, liquids or solids.
How does sound travel?
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1 Sound is produced by _________ of objects.
vibration
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2 Sound must travel through a _________, which can be _________, _________ or _________.
mediumsolids liquidsgases
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3 Sound cannot travel through a _________.vacuum
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The structure of our earThe ear can be divided into:
outer ear (外耳 )
middle ear (中耳 )
inner ear (內耳 )
3D model
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Examining the ear model11.10
human ear model
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11.10
a
b
c
pinna
eardrum
ear canal
outer ear
middle ear
inner ear
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11.10
d
e
f
ear bones
auditory nerve
cochlea
outer ear
middle ear
inner ear
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How do we hear?1 Sound in the surroundings is collected by the pinna.
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 earsWe can only hear sounds within a certain range of frequencies (頻率 ).
• number of vibrations per second
• unit: hertz (Hz)
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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
The limitations of our ears
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Experiment video
What is our hearing range?11.11
signal generator loudspeaker
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11.11
1
Turn it on
signal generator loudspeaker
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Start with the lowest frequency and then slowly increase the frequency.
1
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2 Raise your hand as soon as you hear the sound.
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Record the frequency. This is the lower limit of your hearing.2
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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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Raise your hand again when you can no longer hear the sound.3
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Record the frequency. This is the upper limit of your hearing.3
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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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Humans can only hear sounds within a certain range of frequencies.
The limitations of our ears
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Audible frequency ranges of other animals
goldfish
human
dogdolphin
batSound frequency (Hz)
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Audible frequency ranges of other animals
Sound frequency (Hz)
frequency of dog whistle: 22 000 Hz
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Audible frequency ranges of other animals
Sound frequency (Hz)
sharp enough to draw dog’s attention
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Audible frequency ranges of other animals
Sound frequency (Hz)
too high for humans to hear
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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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transportation
What is noise?
Sources of noise:
construction works
machinery
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What is noise?
loudness (音量 ) of sound /
sound level
measured in decibels (dB) (分貝 )
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high decibel level
mid decibel level
low decibel level
Sound levels of some sounds in daily life
Sound level (dB)
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What is noise?
decibel meter (分貝計 )
used to measure sound levels
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11.6Measuring sound levels at school
Use a decibel meter to measure the sound levels in…
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11.6
Environment Sound level (dB)
1 Classroom with air conditioning on and windows closed
2 Classroom with air conditioning off and windows open
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11.6
Environment Sound level (dB)
4 The street near the front door of the school
3 Playground during recess
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11.6
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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11.7Take 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.
11.7
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The users may not be alert to the traffic conditions on the road. Accidents may result.
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2
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11.7
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
Bomb!
Beep~
If we stay in a noisy environment for a long time …
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Protecting our ears
receptors and nerve cells will be permanently damagedpermanent hearing loss
may result
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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.
VOL
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Protecting our ears
d Do not pick our ears with hard objects.
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Noise controlSome 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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Long term exposure to noise or loud sound may cause mental stress and hearing loss.
Noise pollution
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We should protect our ears from noise.
Noise pollution
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sound in the surroundings
acollected by
pinna
55
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ba pinna ear canal
55
the sound travels along
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cb ear canal eardrum
the sound causes vibrations in
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c eardrum d ear bones
transmits vibrations to
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e cochlead ear bones
magnify vibrations, transmit to
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55
fe cochlea auditory nerve
sends out messages that travel along
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55
g brainf auditory nerve
carries messages to
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55
soundg brain
interprets the messages as
