• Sound are produced by vibration.

• Sound needs a medium to travel.– Sound can travel through solids, liquids and gases.

– Sound cannot travel through a vacuum.

1.8 SOUND AND HEARING

To study the production of sound.

Method:Activities A to C as shown in the table below werecarried out.

Activity Observations Inference

My fingers can feel the vibration of the vocal cords

The vibration of the vocal cords produces sound.

The ruler vibrates and a sound can be heard.

The vibration of the ruler produces sound.

The free end of the tuning fork vibrates and a sound can be heard.

The vibration of the tuning fork produces sound.

The kinetic energy of the vibration is changed into sound energy.

A guitar, a drum and a bell.

vibration.

To investigate the need of medium for sound to travel.

• The tapping sound can be heard at the other end.

• The tapping sound can travel through the pipe (solid)

• The sound of the bell can be heard.

• The sound of the bell can travel through the air (gas).

• As the air is drawn out, the sound of the bell becomes weaker. When all the air is drawn out, the sound of the bell cannot be heard at all

• The sound of the bell cannot travel through vacuum

• The sound of the bell needs a medium to travel.

• As the air is let in the bell jar, the sound of the bell becomes stronger

1

2

3

4

2. Explain why sound cannot travel through vacuum.

There are no particles in vacuum to transfer vibration.

3. Can sound travel through liquids? Explain

Yes. This is because liquids has particles to transfer vibrations.

1. Why does the sound of the bell become fainter in step 2 ?

As the air was drawn out, there were lesser air molecules to pass on the sound vibration. This caused the sound of the bell to become weaker. When all air was drawn out, the vibrations cannot be passed on at all. Therefore no sound was heard.

medium vacuum

Reflection and Absorption of

Sound

1.8 Sound and Hearing

• Bunyi di hasilkan oleh getaran

• Bunyi memerlukan medium untuk di pindahkan

• Bunyi boleh dipindahkan melalui; – Pepejal– Cecair– Gas

• Bunyi tidak boleh dipindahkan dalam vakum

To investigate the reflection and absorption of sound

Hard and smooth

Soft

Loud

Soft and rough

The plank of wood is a good sound reflector because the ticking sound is louder when the plank of wood is used. The towel is a good sound absorber because the ticking sound is softer when the towel is used.

Thick curtains and walls lined with soft board.

reflected

hard

absorbed.

smooth

goodsoft

Defects of

Hearing and

ways to correct them

Hearing Loss

Outer and middle earFirst Type

I nner earSecond Type

· Wax blockage,· A punctures eardrum,· Birth defects,· Ear infections.

· Often temporary.· Treated medically

or corrected surgically

· Process of aging,· Bacterial infections,· A severe blow to the

side of the head,· Extended exposure

to loud sounds,· Tumour in inner ear,· Permanently damage

to receptors in cochlea

· Cannot be treated medically.

· Corrected with the used of hearing aids

Hearing Defects• The most common hearing defect is deafness. Caused by:

•Tearing of eardrum,•Damage to the ossicles,•Damage to the auditory nerves,•Damage to the cochlea due to toxic chemical or exposure to loud sound,

•Damage to the hearing centre of the brain

Device to Overcome Hearing Limitations

• A microphones sends a weak sounds to the loud speaker to increase the volume/ to be amplified.

• The stethoscope increases the volume of the heartbeat or pulse

Device to Overcome Hearing Limitations

• Hearing aids are used by people with hearing defects.

Device to Overcome Hearing Limitations

Stereophonic Hearing

• The ability to hear with both ears.

• Enables us to determine the direction of the sound accurately– The ear closer to the sources of

sound detects the sound slightly earlier and louder than the other ear.

– The brain interprets the difference, thus determining the sources of the sound.

Exercisesound waves

cannot

faster

reflection

medium

stereophonichard

amplifies