SOUNDChapter 14(Physics)

FROM VIBRATION TO SOUND WAVE

Vibration is a to and fro ( backwards and forward) movement about a fixed point.

Any object can make a sound wave when it vibrates.

Sound can travel in gas, liquid or solid (contain particles)

• When an object vibrates it makes the particles next to it in solid, liquid or gas vibrate.

• As the vibrating object moves towards the air particles it squashes them together (high pressure).

• As the vibrating object moves away the air particles spread out(low pressure).

• As the object vibrates the air particles also move forward and backwards and then air particles further away squash and spread out.

• This makes alternate regions of high and low pressure which travel through air away from the vibrating object.

• If the wave is plotted on the graph they make a waveform (shown below)

• Sound travels in all directions.

• Sound cannot travel through vacuum (no particles).

DETECTING SOUND WAVES• Ear is the organ of the body that detects sound

waves.

• The ear is divided into three parts:a) Outer earb) Middle earc) Inner ear

Outer ear

Middle ear

Inner ear

Ear drum

StirrupAnvil

Hammer(auditory)

Sound waves reach the outer ear.

Sound waves pass through the auditory canal.

Sound waves reach the ear drum and make it vibrate.

Waves pass from the ear drum to the three ear bones (hammer, anvil

and stirrup).

The bones vibrate and transfer the vibrations to the cochlea

Cochlea sends the vibration to the fibre (responds to a particular

pitch)

Fibre stimulates the nerve ending

Nerve impulse is sent to the brain where we become aware of the

sound.

• If very loud sounds enter the ears the vibrations in the ear fluid are so strong that they damage the fibres and stop the nerve endings being stimulated.

• This can produce permanent ear damage or deafness.

Reflect• Why do people put a hand to their ear when

they are listening to someone who is whispering?

• Why people wear ear protectors in shooting activities?

OSCILLOSCOPE

• An instrument that allows us to see waves produced by sound.

DESCRIBING A WAVE• Displacement/distance graph is used to show the

different position of particles when a sound wave is produced.

Crest

Trough

• Particle at position X: Rest position• Particle at position Y: Moved the maximum

distance in one direction.• Particle at position Z: Moved maximum distance

in the other direction.

X

Y

Z

• Two characteristics of sound waves:(a)Amplitude (height of crest or depth of trough)(b)Wavelength (distance from top of one crest to

the next / distance from bottom of one trough to the next)

Crest

Trough

THE LOUDNESS OF SOUND

• The loudness of a sound is related to the movement of the particles.

• The loudness of a sound is measured in decibels.

• Loud sound (large amplitude, large amount of energy)

• Quiet sound (small amplitude, small amount of energy)

• The sound wave energy is changed to movement energy in the eardrum and ear bones.

LOUDNESS AND DEAFNESS

• Very loud sound (strong vibration) can cause a hole in the eardrum (strong pushing and pulling force).

• Eardrum (perforated) does not vibrate properly.

• The eardrum can heal and normal hearing restored.

• If exposed to a particular note for a long time, the person will no longer be able to hear it.

• This is due to the nerve damage of the nerve ending in the cochlea for that note.

• A common cause for partial deafness, is the development of ear wax.

• The ear wax can be removed under the medical supervision of a nurse.

Ear gets blocked by wax

Accidents or loud bangs can damage the eardrum

Middle ear can get infected

Older peoples bones may fuseNerve cells in the cochlea degrade with time

Loud noise may damage the cochlea

This can be treated with antibiotics

This might repair itself

This prevents vibration

There is no cure for thisSignals are not sent to the brain

A doctor can wash this out

How might our ears become damaged?

A high pitch sound A low pitch sound

The shorter/longer the wavelength of the wave on the trace; the lower/higher the frequency of the sound

The more waves you see, the higher the pitch/frequency

Pitch (or frequency)

Which trace represents the highest pitched sound?

A‘A’ is the highest pitched sound because it has the shortest wavelength/most number of waves visible.

Oscilloscope Traces

B

What can I hear?

Increase frequency of signal on the generator whilst keeping the volume the same.

The lowest frequency I can hear is ________ Hz The highest frequency I can hear is ________ Hz

2020 000

http://www.youtube.com/watch?v=RC8SV3L3bo0

Hearing Ranges

0 1 10 100

1,000

10,000

100,000

1,000,000

Frequency [Hz]

Moths

Elephants

Mice

Humans

Pigeons

Bats

Hearing Ranges of Animals

Ani

mal

Which animal can hear the lowest frequency?

Which animal can hear the highest frequency?

moths