8 l sound & hearing (boardworks)

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KS3 Physics

8L Sound and Hearing



Contents

What is sound?

Speed of sound

The ear and hearing

Summary activities

Reflecting sound


What causes sound?

The tuning fork vibrates and you hear a sound.

Sounds are made when an object vibrates.

Take a tuning fork and strike it against a block of wood.

What do you observe?


Good vibrations!

What vibrates so that the following make sounds?

violin strings

voice box

loudspeaker cone

drum skin


Remove the air from the bell jar and what happens to the sound?

The bell-jar experiment

Place a ringing clock inside the bell jar and what happens?

There is air inside the bell jar so the sound can travel and be heard.

The sound cannot be heard because there is no air inside the bell jar (a vacuum).

vacuum pump on


Sound waves can be studied with this type of equipment.

signal generator

oscilloscopeloudspeaker

Studying sound waves

A signal generator produces different types of signals.

A loudspeaker converts signals from the signal generator into sound waves.

An oscilloscope shows wave patterns and allows us to ‘see’ sound.


The larger the amplitude of the wave on the trace, the louder/quieter the sound.

Loudness and amplitude

A sound can be quiet or loud.

loud soundquiet soundOn an oscilloscope trace, the loudness of a sound is shown by the height of the wave. This is called the amplitude.

Which word should be crossed out in this sentence?


Which is the loudest?

Sound A is the loudest.

Which trace represents the loudest sound?

Sound A has the largest amplitude (i.e. the tallest waves), so it is the loudest of these two sounds.

A B


Pitch and frequency

A sound can be high or low – this is the pitch of the sound.

low pitch sound high pitch soundOn an oscilloscope trace, the pitch of a sound is shown by how many waves there are. This is called the frequency.

Which word should be crossed out in this sentence?

The greater the number of waves across the oscilloscope trace, the lower/higher the frequency and pitch.


Which is the highest?

Which trace represents the sound with the highest pitch?

Sound B is the highest pitched.

Sound B has the most number of waves across the oscilloscope – it has the highest frequency and so has the highest pitch.

BA


Wave animation



Contents

What is sound?

Speed of sound

The ear and hearing

Summary activities

Reflecting sound


100 m

00:0000

START

00:0034

STOP

1. When you see the cymbals crash, press START.

2. When you hear the cymbals crash, press STOP.

This investigation to calculate the speed of sound should be carried out in a quiet open space.

Speed of sound experiment


Experiment

distance (m)

time(s)

speed(m/s)

1

2

3

4

Record the results of the sound experiment.

=294 m/s distance

timespeed = =

100

0.34

100 0.34 294

Speed of sound experiment – results table

How are these values used to estimate the speed of sound?


Use the results of the cymbals experiment to calculate the average speed of sound.

How does this calculation for the average speed of sound compare with the real speed?

The speed of sound in air is about…

What errors could have affected the results of the cymbals experiment?

340 m/s

Do you think the speed of sound in water is the same as the speed of in air?

Speed of sound experiment – results


Sound in different states of matter

Sound needs a substance to travel through and travels by particles vibrating.

The particles in a solid are closer together than in a gas or a liquid. This means vibrations are more easily passed from particle to particle and so sound travels faster.

gassolid liquid

Sound waves travel fastest through solids.

Which state of matter does sound travel fastest through?


Sound need particles to travel and the type of substance affects the speed of sound.

330 350

1450

5000

6000

0

1000

2000

3000

4000

5000

6000

7000

air at 0 C air at 30 C water concrete steel

material

sp

eed

of

so

un

d (

m/s

)

Speed of sound in different materials


Which of these travel faster than the speed of sound in air?

distance (m)

time (s)

speed(m/s)

small aeroplane

600 5

jet fighter 900 2

cheetah 50 2.5

meteorite 10 000 0.35

120

450

28,571

20

Breaking the sound barrier!

The jet fighter and the meteorite travel faster than the speedof sound in air – this is called breaking the sound barrier.


Usually, you see lightning before you hear thunder. Light travels much faster than sound.

The speed of light is…

During a thunderstorm, thunder and lightning are created at the same time.

Which do you notice first?

How could you use thunder and the speed of sound to estimate how far away a thunderstorm is?

300,000,000 m/s

How much faster is light than sound?

Sound or light – which is faster?



Contents

What is sound?

Speed of sound

The ear and hearing

Summary activities

Reflecting sound


The sound wave is reflected back from the surface.

This is called an echo.

What happens when a sound wave meets a hard flat surface?

Reflected sound


1. Use a starting pistol (or clapper board) to make a sound.

2. Measure the time taken between firing the pistol and hearing the echo.

START

150 m

Stand at least 100 m from a large, flat wall with a stop watch.

STOP

Echo experiment


How can you use this result to estimate the speed of sound?

The sound of the starting pistol takes 0.92 s to travel a distance of 300 m.

=326 m/s

distance

timespeed =

=300

0.92

Repeat the experiment several times to obtain an average.

Echo experiment

How does your calculation for the average speed of sound compare with the real value?compare with the real value?


Questions on reflecting sound

1. What is a reflected sound called?

an echo

2. Are hard or soft surfaces best at reflecting sound?

3. Why are there soft materials on the walls of cinemas and theatres?

to reduce echoes

4. Name two animals that use echoes for navigation or communication.

bats and dolphins

hard surfaces



Contents

What is sound?

Speed of sound

The ear and hearing

Summary activities

Reflecting sound


The ear and sound waves


1.Sound waves are collected by the ear lobe or pinna.

2.The waves travel along the ear canal.

3.The waves make the ear drum vibrate.

4.The small bones (ossicles) amplify the vibrations.

5.The cochlea turns these into electrical signals.

6.The auditory nerve takes the signals

to the brain.

3

4

5

6

1

2

How does the ear hear?


Set the volume and increase the frequency of the signal provided by the signal generator.

20 Hz to 20,000 Hz

Humans can only hear sounds of certain frequencies.

What is the hearing range of a healthy young person?

The range of frequencies a person can hear is called their hearing range.

Hearing range


100,000

10,000

1,000

100

10

1

0

human dog elephantbat mouse dolphin

Which animals hear the lowest and the highest frequencies?

frequency(Hz)

Comparing hearing ranges


We all have slightly different hearing ranges People lose the ability to hear sounds of high frequency as they get older.

Almost 1 in 5 people suffer some sort of hearing loss.

Temporary hearing loss may be caused by ear infections and colds, after which hearing recovers.

Permanent hearing loss and deafness can be present at birth or occur if the ear is damaged or diseased.

Does everyone have the same hearing range?

Hearing ranges and hearing loss


160

140

120

100

80

60

40

20

0

permanent ear damage

can just be heard

aircraft overhead

decibels

circular saw at 2m

quiet countryside

pin being dropped

loud bell

personal stereo

Measuring loudness – the decibel scale


Noise and its effects

A noise is any unwanted sound.

What one person considers noise another person might not. Can you name any examples?

Noise can cause hearing problems. List three effects of noise.

2. nausea

1. headaches

3. deafness

List three ways of reducing the effects of loud noise.

1. ear protectors

3. putting noisy machinery in insulated rooms

2. double glazing



Contents

What is sound?

Speed of sound

The ear and hearing

Summary activities

Reflecting sound


Glossary

amplitude – The height of a wave, which shows how loud a sound is.

cochlea – The part of the inner ear that changes vibrations into electrical signals which are then sent to the brain.

decibel – The unit for measuring the loudness of sound (dB). eardrum – The thin membrane in the ear which vibrates

when sound reaches it.frequency – The number of waves per second, which

shows the pitch of a sound.hertz – The unit of frequency (Hz). 1 Hz = 1 wave per second.oscilloscope – An instrument that shows a picture of sound.pitch – How high or low a sound is.sound – A form of energy produced by vibrations, which is

detected by the ears.


Anagrams


Multiple-choice quiz

8 l sound & hearing (boardworks)

Education

loudest sound

sound b

sound travels

average speed of sound

loud soundquiet sound

real speed

ms distance time speed

highest pitch