11.5

How do we hear?How do we hear?

Put two fingers gently on your throat while you speak.

What do you feel?

How is sound produced?

Sound is produced by Sound is produced by vibrations vibrations (( 振動振動 ))..Sound is produced by Sound is produced by vibrations vibrations (( 振動振動 ))..

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- All sound sources, like loudspeakers, tuning forks, guitars and flutes, have the parts that vibrate.

The loudspeaker vibrates,so the balls move up and down.

The tuning forkvibrates, soripples form.

- When the tuning fork vibrates,

=> => the surrounding air particles vibrate.

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=> => the vibrations are transmitted from one place to another.

sound wave

sound wave

=> => the relevant parts of the ear vibrate.

- When the vibrations reach the ear,

=> => sound is heard.

How is sound transmitted?How is sound transmitted?How is sound transmitted?How is sound transmitted?

- Musical instruments produce Musical instruments produce vibrationsvibrations in the air. These vibrations are in the air. These vibrations are transmitted totransmitted to our ears. our ears.

p.94p.94Ear Ear - divided into three parts

outer earouter earouter earouter ear middle earmiddle earmiddle earmiddle ear inner earinner earinner earinner ear

tube tube leading leading to throatto throat

with a tube leading to throatwith a tube leading to throatfull of fluidfull of fluid

Structure of earStructure of earStructure of earStructure of ear

outer ear ear canalear canal

ear flapear flap

eardrumeardrumcochleacochleacochleacochlea

auditory nerveauditory nerveauditory nerveauditory nerve

inner ear

ear bonesear bones

middle ear

What are the functions of What are the functions of different parts?different parts?

What are the functions of What are the functions of different parts?different parts?

Activity Corner Activity Corner HH p.94p.94

How does the ear work?How does the ear work?

Read the sentences on the next page.Arrange them in an order which bestdescribes the working of the ear.

A The messages are sent along the auditory nerve to the brain. The brain interprets these messages as sounds.

B The three ear bones magnify the vibrations in the eardrum and pass them to the inner ear.

C The ear flap collects sound vibrations in the air.

D The eardrum vibrates when sound vibrations hit it.

F The sound vibrations travel along the ear canal to the eardrum.

E The liquid in the inner ear vibrates. The sensory cells inside the cochlea detect the vibrations and change them into messages.

Order : C __ __ __ __ AFF DD BB EE

Ear bonesEar bonesEar bonesEar bones

- Magnify the vibrations from the eardrum by 50 times.

- The smallest bones in human body. Among them, the smallest one is only 33 mm long.mm long.

Have you experienced fullness in the ears when descending in an aircraft or a lift?

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This is because of the increasing pressure pushing the eardrum inwards.

NormalNormalNormalNormal DescendingDescendingDescendingDescending

PPAA == atmospheric pressureatmospheric pressure

PPMM == pressure inside middle earpressure inside middle ear

You can ease the fullness simplyYou can ease the fullness simplyby by swallowingswallowing. This . This equalizes equalizes the airthe airpressure at both sides of thepressure at both sides of the eardrum eardrum. .

Put a burning candle in front of theloudspeaker, what will happen to thecandle flame?

The candle flame moves back and forth.

The paper disc of the loudspeaker vibrates, so the candle flame moves in the same direction as the surrounding air.

- Sound cannot be transmitted if there is no medium. e.g. aire.g. air

Why can we hear the noiseWhy can we hear the noisecoming from constructioncoming from construction

works in the flatworks in the flatnearby?nearby?

p.92p.92How can sound be transmitted?How can sound be transmitted?

- Sound can travel through solids, liquids and gases.

In ancient times, a soldier placedhis leather arrow sheath on the groundto hear the sounds of horses of the enemies.

Shen Kuo ( 沈括 ) inthe Northern Songperiod gave a correct scientific explanation of this.

- Divers under water can hear the sounds of motorboats. - It is believed that dolphins make sounds and ‘talk’ to each other under water.

Can sound travel Can sound travel

through athrough a vacuum vacuum??

to electricity supply

electric bell

to vacuum

- There is no air in outer space to transmit the sound.

Astronauts can only talk to each other using radio waves.

Sound travels at different speedsin different media. air 330

water 1430

medium speed (m/s)

steel 5030

Can you explain this using the Can you explain this using the

particle theoryparticle theory??

Can you explain this using the Can you explain this using the

particle theoryparticle theory??

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Lightning always come before thunderstorm. Do you know why?

The best toy telephoneThe best toy telephoneThe best toy telephoneThe best toy telephone

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Lily is not satisfied with the sound quality of the toy telephone she used inExperiment Centre 11.4. She wants to make abetter one!

Little Scientist

Below are some of her questions:

11 Is it better to use a thick or thin string?

22 What material should be used to make

the cups?

33 Does the size of the cups make

a difference?

44 Does the length of the

string joining the cups

make a difference?

What are your answers to Lily’s questions? What are your hypotheses?

Design your Design your investigationsinvestigations..

Carry them out and use Carry them out and use your findingsyour findings to make the best toy telephone.to make the best toy telephone.

Design your Design your investigationsinvestigations..

Carry them out and use Carry them out and use your findingsyour findings to make the best toy telephone.to make the best toy telephone.