MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 8la1
8La1 Making different sounds
Name _____________________________ Class ____________
Method
Apparatus
- Tuning fork - Ruler
- Rubber band - Tripod
- Pencil case - Pencil
- Test tube - Rubber bung
- Beaker of water
Take care near to eyes.
1 Make the tuning fork vibrate by hitting the rubber bung. Complete the following sentences using words from the box below.
a When I hit the rubber bung I noticed that the prongs _________________ .
b I then placed the prongs into the beaker of water and the water _________________
out. This was because the prongs were _________________ .
c I placed the end of the vibrating tuning fork on my hand, my temple and my leg. The
part of the body which felt the vibrations most was my _________________ .
hand leg splashed temple vibrated vibrating
2 Now try putting the vibrating tuning fork on the other pieces of apparatus.
Try to make a sound with each piece of apparatus.
3 Record all your results on the next page.
Recording your results
Underneath each item write down:
- what happened when you put a vibrating tuning fork on it.
- how else you could make a sound with it.
- what it sounded like.
______________________________________
[ knowledge, observing, considering ]
8La2 What makes the sound?
Choose 10 sounds from the picture above. Complete the table below.
Sound
Source of the sound (what is making the sound?)
[ knowledge, literacy ]
8La3 Common sounds
1 Make a list of eight sounds in this picture.
2 Write down five other sounds that you can think of.
3 Put your sounds into a table like the one below. Some can go into more than one list.
4 Which list had most sounds in it?
5 Did your unpleasant sounds have anything in common? For example, were they very loud or screechy, or both?
6 Some people cannot hear very well, or cannot hear at all. Imagine what life would be like if nobody could hear anything. Think about all the things you hear, like car horns, school bells, music, people talking. Describe what the world would be like if sound could not be used at all.
8La4 Comparing sound and light waves
Light and sound waves are both forms of energy. There are two ways that energy can travel in waves; by longitudinal or transverse waves.
A slinky can be used to show the way that waves travel.
If you hold the slinky at one end and give it a short sharp push at the other, you can see a wave moving along the slinky. This is called a longitudinal wave. The vibrations are in the same direction as the wave. This is how sound waves move.
When a sound wave travels through air, the particles are first pushed together or compressed and then spread apart or rarefied. These areas are called compressions and rarefactions.
Light does not need a substance to move through, but we can use a slinky to help us to think about how light waves travel. To show a model of a light wave you need to move the slinky sideways or up and down. The vibrations are at right angles to the direction the wave is moving. This is called a transverse wave. Other examples of transverse waves are radio waves, X-rays and ultraviolet light.
1 What is the difference between longitudinal and transverse waves?
2 Draw and label each wave type and say which represents a light wave and which a sound wave.
3 What sort of wave is produced when air particles are compressed and rarefied?
4 Give three examples of transverse waves.
5 What type of wave is a sound wave?
8Lb1 Changing the pitch 1
How do you change the pitch of a sound?
The pitch of a note is how high or low it sounds.
1 When I added more water and blew across the top of the bottle the pitch of the sound
went _______________ (up/down).
2 The longer nails had a _______________ (higher/lower) pitch.
3 The shortest wind chime had the
_______________ (lowest/highest) pitch.
4 I dropped each piece of wood from the same height.
The longest piece of wood had the
_______________ (highest/lowest) pitch.
5 I put several different width rubber bands across the hole in the box. I twanged each rubber band. The thinnest band had the
6 I made a ruler vibrate on the edge of the table. I changed the length of the ruler and vibrated it again. The longer ruler gave the
________________ (higher/lower) pitch.
Conclusion
The longer the thing which is vibrating the _______________ (lower/higher) the pitch.
[ observing, considering ]
8Lb2 Changing the pitch 2
You are going to find out what factors affect the pitch of a note.
Remember:
- pitch is how high or low the note sounds
- frequency is the number of vibrations every second
- the higher the frequency the higher the pitch.
1 For each piece of apparatus in the drawings below, write down what is vibrating to make the sound.
2 Change the length of the thing that is vibrating.
3 What do you notice about the vibrations when the thing that is vibrating is longer? Write down your observations.
4 What do you notice about the pitch? Write down your observations.
A
B
C
D
E
F
Considering your results/conclusion
1 Write a conclusion about your investigations. Make sure you write about the speed of the vibrations, the pitch of the sound and the length of the thing that is vibrating.
Evaluation
2 Which factors did you keep the same in these investigations?
3 Choose one investigation and say how you could improve it. Write a plan to carry it out. Show your plan to the teacher. If there is time your teacher may let you try it out.
[ planning, observing, considering, evaluating ]
8Lb3 Vibrations, pitch and frequency
1 Complete the sentences using words from the box. Some words can be used more than once.
All musical instruments make a sound because something _______________ . Instruments
like violins produce a _______________ pitched sound. This means that the strings are
vibrating at a high _______________ .
An oscilloscope can show a sound wave on a screen when it is connected to a
_______________ . When the waves on the screen are very close together they show that the
sound waves have a high _______________ . Waves which are far apart show sound waves
with a _______________ frequency.
The frequency of a sound wave is the number of _______________ that pass a point every
second. The loudness of a sound is shown by the _______________ of the waves. Half the
height of a wave is called the _______________ . The bigger the amplitude of the wave the
_______________ the sound.
The unit for frequency is the _______________ (Hz). A frequency of 50 Hz means that 50
_______________ pass every second.
amplitude frequency Hertz height high lower louder
microphone vibrates vibrations waves
2
a Which two sounds have the same loudness or volume? __________________________
b Which sound wave has the highest frequency? ________________________________
c Which sound wave has the lowest frequency? _________________________________
d Which sound wave has the lowest pitch? ____________________________________
e Which sound wave is twice as loud as the sound in D? __________________________
8Lb4 Comparing frequencies
Animals and instruments can produce a wide range of sounds with varying frequencies. Some animals can hear frequencies of sound that humans cannot hear.
1 a Which instrument can produce the lowest pitch?
b Which instrument can produce the highest pitch?
c Which instrument has the widest range?
d Why does the midi system have the widest range of frequencies?
2 Plot a chart like the one above to show the frequencies in the table. Use two colours (or different shading) to show the pairs of values.
Animal
Frequencies they can make (Hz)
Frequencies they can hear (Hz)
cat
750 - 1600
60 - 65000
dog
450 - 1000
15 - 50000
robin
2000 - 13000
250 - 21000
human
80 - 4100
20 - 20000
grasshopper
7000 - 10000
100 - 15000
bat
10000 - 120000
1000 - 120000
a A dog whistle has a frequency of 25 000 Hz. Which animals can hear it?
b Why do dog owners use a whistle that they can't hear?
c Which animal has the widest hearing range?
d Which animal can produce sound waves with the lowest frequencies?
e Which animal can make and hear sound waves with the highest frequency?
f Which animals hear a wider range of frequencies than humans?
[ knowledge, numeracy ]
8Lb5 Musical instruments
piccolo double bass Not to scale.
Sounds can have a high or a low pitch. High pitched sounds, like a squeaking mouse or a piccolo, are made by waves with a high frequency. Low pitched sounds, like a rumbling stomach or a double bass, are made by waves with a low frequency. Frequency is the number of vibrations each second and it is measured in hertz (Hz).
Most music is based on a scale of notes, which are arranged with rising or falling pitch. Western music is based on notes named using the first seven letters of the alphabet - A, B, C, D, E, F, G. The difference between two notes of the same name, such as C to C, is called an octave. The frequency of the higher C is twice that of the lower C.
1 Explain what high and low pitched sounds are and give an example of each.
2 Look at the diagram of the piano keyboard.
a What are the two missing frequencies?
b What is the frequency of the note an octave higher and an octave lower than the A note shown?
3 Look at the diagram showing the frequencies of different instruments.
a Name two instruments with overlapping frequencies.
b Name two instruments which do not have overlapping frequencies.
c Apart from the piano, which instrument has the greatest range?
d Choose three other instruments and estimate their frequency ranges.
4 Pan pipes have been known for over two thousand years. They are played by blowing across the individual tubes.
a How many octaves do these pan pipes have?
b How many notes can you play on the pan pipes?
c What vibrates to create the sound?
5 The sitar is a popular Indian instrument.
a What vibrates to create the sound?
b What is its frequency range?
c How does this compare to a guitar?
6 Find out more about a sitar, a tabla or pan pipes and produce a poster for the class. You could use the library, the internet or ask someone who plays the instrument.
[ knowledge, numeracy, research ]
8Lc1 Travelling sound 1
- Stethoscope
- 2 pieces of wood
- Tank of water
Make sure the earpieces in the stethoscope are kept very clean or use disposable earpieces
Label the diagram using words from the box.
stethoscope material being tested two pieces of wood
Fill in the gaps in these sentences, using words from the box.
I will knock the pieces of ________________ together. I will use the
________________ to listen to the sound. I will record how well I can
gases
hear
materials
stethoscope
wood
________________ the sound travelling through different materials. Sound
travels at different speeds through solids, liquids and ________________ .
Object
Solid/liquid/gas
How well I could hear
Considering your results/conclusions
I could hear the sound best through the ______________ . I could hear sound least
well through the ______________ . Sound travels quickest through _______________
________________ and slowest through ________________. Sound travels through a
________________ faster than through air but slower than through a solid.
solid
liquid
gas
solids
8Lc2 What can you hear?
1 Under each picture put a tick if you can hear it and a cross if you cannot.
2 If you can hear a sound, say what is vibrating and what the sound is travelling through to reach the ear.
3 If you cannot hear a sound, say why not.
_________________________
[ knowledge ]
8Lc3 Sound and particles
Everything is made of very small bits called particles. Sound waves travel because vibrating particles pass their vibrations from one particle to the next. Particles need to touch each other for this to happen.
Particles in a solid are very close together. They are held together with strong bonds. Sound vibrations can move very quickly because the particles are close to each other and it is easy for the vibrations to be passed on.
Particles in a liquid are fairly close together. They are able to move about. Sound vibrations move more slowly than in a solid because the particles are a bit further apart and do not touch each other as often.
In a gas the particles are very far apart. They can move easily in all directions. The particles do not touch each other very often so it is more difficult for vibrations to be passed on. Sound vibrations travel more slowly in a gas than they do in solids and liquids.
As well as travelling at different speeds in solids, liquids and gases, sound travels at different speeds in different solids, or different liquids. Sound travels much faster in steel than it does in wood, for example.
1 How do sound waves travel?
2 What does vibrating mean?
3 In which picture are the particles furthest apart?
4 Explain why sound travels quickest through a solid.
5 Why does sound not travel in a vacuum?
6 Put these in order of how fast sound travels through them. Start with the fastest: air, space, water, rock.
7 Why do you think sound travels faster in steel than it does in wood? (Hint: Think about the densities of the two materials, and how the particles might be arranged.)
8Lc4 Travelling sound 2
Sound travels through different materials at different speeds. This is because materials vary in density. Sound travels very quickly through dense materials because the vibrations are passed along quickly as the particles are in close contact. Sound does not travel through air very well because gases have particles which are far apart and they need to touch to pass on the vibrations.
Material
Speed of sound in m/s
steel
6000
aluminium
5100
iron
5000
concrete
glass
4500
copper
3700
brick
3000
salt water
1560
water
1500
mercury
1450
ethanol
1200
air
330
oxygen
316
carbon dioxide
260
1 Plot a bar chart to show the speed of sound in these materials.
2 a Which two materials are the most dense?
b Which two materials are the least dense?
c Which material allows sound to travel 4 times faster than in water?
d Sound travels though cork half as fast again as it does through air. What is the speed of sound through cork?
3 Michael is sitting in a boat with a metal hull. He is hammering the bottom of the boat.
a Who will hear the sound first, Nasim or Nicola?
b Explain your answer to part a.
4 For each jar say whether you can hear the bell ringing and explain your answer.
A B C
contains air contains no air contains no air
5 You can send a message to someone in the next room by tapping on a radiator. In which system will the message will travel fastest - one made of copper, iron or steel?
6 Copy and complete these sentences.
Sound is caused by _________________ . Sound cannot travel through a
_________________ . The speed of sound in a solid is _________________ than it is in air.
This is because a solid is more _________________ than air.
8Lc5 Sound history
Scientists have known for many years that sound travels through different materials at different speeds.
Sir Isaac Newton (1642-1727) was the first to calculate the speed of sound in air. His figure was too low by 13%, but this was very close for the measuring equipment available at the time.
A hundred years ago two people on Lake Geneva measured the speed of sound in water. One made a signal and started ringing a bell under water. The other started his stopwatch and held his head under water until he heard the bell.
In 1787, Ernst Chladni (1756-1827) was the first person to study sound patterns on solids. He used flat plates, now known as Chladni plates, to study how flat surfaces vibrated when sound waves passed through them.
In 1866, August Kundt (1839-1894), a German physicist, developed a method for working out the speed of sound in different gases. In his experiments, Kundt dusted the interior of a tube filled with a particular gas with a fine powder to show the position of the sound waves, and he was able to use this to calculate the speed of the waves.
The speed of sound in a material depends on how easy it is for the particles to pass on vibrations. The closer the particles the faster the speed of sound, which is why sound travels fastest through solids and slowest through gases. The speed of sound is also affected by temperature. A higher temperature means that the particles are moving faster because they have gained energy.
1 The speed of speed of sound in air is 331 m/s at 0 °C. At 20 °C (room temperature), sound travels at 343 m/s. Explain why there is a difference.
2 What did Sir Isaac Newton work out the speed of sound to be in air at room temperature?
3 Who was the first scientist to work out the speed of sound in different gases? Explain how and when he did this.
4 a How was the speed of sound in water calculated 100 years ago?
b What did the two people need to do to ensure that the experiment was fair and accurate?
5 The speed of sound in water is 1500m/s and in brick it is 3000m/s.
a What do you think the speed of sound in wood is? Choose from the following:
A 300 m/s B 1300 m/s C 3300 m/s D 5300 m/s.
b Explain why you have chosen your answer.
6 How do the following affect the speed of sound?
a density b temperature
7 Draw and illustrate a time line to show when discoveries about the speed of sound took place.
[ literacy, numeracy, knowledge ]
8Ld1 What can we hear?
- Signal generator
- Oscilloscope
- Loudspeaker
Tell your teacher if any sounds are uncomfortable.
Prediction
1 The range of frequencies that you can hear tends to become narrower as you get older. Who do you think will have the narrowest range in your class?
Your teacher will change the frequency of the signal generator, and tell you what each frequency is. Write down the lowest and highest frequencies that you can hear.
2 Collect your group's results and plot a bar chart to show them. Your axes should look like this:
3 Describe the shape of the graph. Did everyone have similar results or was there a spread?
4 Was this what you expected to find?
5 Were any of the results surprising? If so, why?
6 Was it a fair test? For example, were the tests repeated? Was everyone the same distance from the loudspeaker?
7 If you had time how could you improve the experiment?
[ observing, considering, evaluating ]
8Ld2 Ear jigsaw
1 Cut out the jigsaw pieces and arrange them to show the ear.
2 Stick the pieces into your book.
3 Fill in the label boxes with words from the box below.
outer ear sound waves enter ear canal ear drum
ear bones cochlea auditory nerve
---------------------------------------------------------------------------------------------------------
8Ld3 Ear diagram
1 Fill in the label boxes in the diagram with words from the box.
ear drum auditory nerve outer ear
sound waves travelling ear canal ear bones cochlea
2 Write the correct words from the list above next to each of these statements:
a Sound vibrations travel through the air. ________________________
b The sound waves are funnelled into the ear by this. ________________________
c The sound waves travel along this. ________________________
d This part starts to vibrate. ________________________
e These small bones pass the vibrations to the cochlea. ________________________
f This spiral tube contains a liquid and sense cells. ________________________
g This nerve carries electrical signals to the brain. ________________________
8Ld4 Ears and hearing
1 Copy and complete the summary below using words from the box.
Something vibrates to produce a sound. Sound travels through _______________ to the ear.
When the vibrations reach the eardrum they are transferred to the small _______________
called the hammer, anvil and stirrup. The bones pass the vibrations to the _______________ .
This contains sense cells which change the vibrations to _______________ signals called
impulses. The auditory nerve takes the _______________ to the brain. We hear the sound
when the message reaches the _______________ .
air bones brain cochlea electrical impulses vibrations
2 Use the questions and answers below to write sentences about the ear. The first one has been done for you.
a The ear changes sound energy to electrical energy.
a What energy change takes place in the ear?
b What happens as you get older when the small ear bones get joined together?
c What is the treatment for infection in the middle ear?
d Does wax in the ear cause permanent or temporary deafness?
e Why does wax in the ear affect hearing?
f What is an oscilloscope?
g What is a stethoscope?
h What does a hearing aid do?
- a course of antibiotics
- loss of hearing
- sound to electrical
- an instrument for listening to sounds in the body
- it prevents the vibrations reaching the ear drum
- a machine which shows sound waves on a screen
- it helps people to hear
- temporary deafness
3 Write the names of each part of the ear (A-F) in your book.
8Ld5 The stethoscope story
Doctors use stethoscopes to listen to sounds in the body, particularly the heart and lungs. Before the stethoscope was invented, a doctor had to put his ear to a patient's chest or back to listen to the heartbeat. Sound travels better through solids than air so this was possible. However, layers of clothes or fat tend to slow the sound vibrations and make them difficult to hear.
In 1816, a French doctor, Théophile Laënnec (1781-1826), thought that there must be a better way of listening as it was often inconvenient and 'in the case of females, indelicate'. One day he was examining a girl who had symptoms of heart trouble when he had an idea. He rolled up his newspaper and put it on her chest. He could hear her heart much more clearly. From this idea Laennec invented a simple stethoscope.
The modern stethoscope is based upon Laënnec's idea.
The modern stethoscope is made up of a Y shaped flexible plastic tube. An earpiece is attached to each end of the Y and a sound detecting device at the other end. The sound detecting device has a thin plastic sheet on one side and a bell shape with a hole in on the other. The diaphragm is used to listen to a patient's chest for high pitched sounds. The bell end is used to detect lower pitched sounds. The lung sounds have a higher frequency than heart sounds.
1 How did doctors listen to heart sounds before the stethoscope was invented?
2 What were the disadvantages of this method?
3 What was the name of the doctor who invented the stethoscope?
4 The modern stethoscope has an earpiece for each ear.
a Why is this an improvement?
b Why must the earpieces fit snugly in the doctor's ears?
c Why must the earpieces be kept very clean?
5 Why are there two different sides to the end of the stethoscope?
6 Which side is used for listening to:
a the heart
b the lungs?
8Ld6 Ultrasound scans
Sound waves that have a frequency which is too high for us to hear are called ultrasound. These sound waves can be used to check on a baby's progress before it is born. They are much safer than X-rays because X-rays can damage cells in the body of mother and baby.
First, a special gel is spread over the mother's abdomen. This makes sure that the ultrasound waves can get from the probe into the woman's abdomen. The ultrasound is reflected by the fetus, and the echoes are detected by the probe. The probe sends information to the computer, which turns it into a picture on the screen.
Doctors can use the probe to check that the fetus is developing properly. The scanner produces moving pictures, so sometimes the fetus's heart can be seen pumping. Sometimes the doctor can tell the mother what sex her new baby will be.
1 What do we call sound waves we can't hear?
2 Why are ultrasound waves used to scan a mother's abdomen?
3 a Which parts of your body show up on X-rays?
b Which parts of a baby's body show up on an ultrasound scan?
c Give two reasons why is it better to use ultrasound instead of an X-ray. Explain your answers.
4 Why is a special gel used?
5 a How could a doctor tell the sex of an unborn baby?
b Doctors cannot always find out the sex of the baby. Why not?
6 Why is it useful to have a moving picture?
7 There are other medical uses of ultrasound. Find some examples.
[ knowledge, literacy, research ]
8Le1 Soundproof design 1
Materials which are good at reducing sound levels are usually soft and with many layers. They are called sound insulators.
- Electric bell - Cardboard box
- Materials to test - Sound intensity meter
- Cells or power pack
Label the diagram using words from the apparatus list.
I think the best material for soundproofing will be _______________ , because it is the
______________________________________________________________________________ .
I am going to test different materials to see which makes the sounds _______________
(quieter/louder). The material which makes the sound quietest is _______________ (best/worst) at
soundproofing. It is a _______________ (good/bad) insulator.
I am going to record the _______________ (sound/light) level on the meter.
I will record my results in the table on the next page.
Sound level in decibels
Draw a bar chart to show your results.
The material with the lowest sound recorded was ______________ . I think this was a good sound
insulator because it was______________ (hard/soft) and had ______________ (many/few) layers.
I could have improved my experiment by _____________________________________________
_______________________________________________________________________________
[ observing, presenting, considering, evaluating ]
8Le2 Soundproof design 2
Planning
1 Decide which materials you will use for soundproofing your box.
2 What factors will you need to keep the same?
3 Write a method for your investigation. You will need to think about these things:
- Something to make a sound
- Cardboard box
- Assorted materials
- Sound intensity meter
- How much of each material will you use?
- Are you going to compare different materials or different numbers of layers of the same material?
- What will you use to make a sound?
- How far away will you hold the meter?
- How often will you repeat the measurements?
- What will you have to keep the same to do a fair test?
4 Design a table to record your results.
5 Show your method to your teacher before you begin.
6 Which of your materials do you think will be best for soundproofing? Explain why you think so.
7 Record your results neatly in a table.
8 Plot a graph to show your results, using axes like these:
9 Describe the shape of the graph. Did everyone have similar results or was there a spread? Was this what you expected to find?
10 Were any of the results surprising?
11 If you had time how could you improve your experiment?
[planning, observing, presenting, considering, evaluating ]
8Le3 Noise nuisance 1
The loudness of a sound is measured in decibels (dB). A sound which is 0 dB is so quiet that we can only just hear it.
1 Look at the pictures showing different sounds. Join the pictures to the scale to show how loud you think the sounds are. Some have been done for you.
2 Fill in the gaps in these sentences using words from the box below or information from the pictures above.
The units for measuring the loudness of a sound are _______________ . We cannot hear any
sounds quieter than _______________ dB.
When leaves rustle, they have a loudness of _______________ dB. People usually talk with a
loudness of _______________ dB.
Loud noises can _______________ our ears and make us deaf. A very loud noise can break
the _______________ . The cochlea can also be damaged by _______________ noise.
There are laws to protect people who work in noisy _______________ . The loudest sound
allowed is 90 dB. This is the same loudness as a _______________ _______________ .
_______________ _______________ and explosions are louder than this.
damage decibels eardrum factories loud
police sirens road drill
8Le4 Noise nuisance 2
1 Any sound above 80 decibels is painful to the ears. Name six sounds which are painful.
2 What is the loudness in decibels which causes immediate damage to the ears?
3 What is the loudness in decibels of:
a a road drill? b a police siren?
4 The loudness of singing is 10 decibels higher than normal speech. What is the loudness of singing?
5 The loudness made by a motor cycle and paint sprayer have a similar loudness. What is it?
6 Many people used to work in noisy factories without ear protection. The table below shows the percentage of workers who suffered hearing loss after working in the factories for many years.
Noise level in
Workers who had hearing loss (%)
factory (dB)
Age 20 years
Age 30 years
Age 40 years
Age 50 years
90
0
7
12
18
100
22
37
42
110
5
45
67
75
a What percentage of workers suffered hearing loss aged 40 after being exposed to levels of:
i 90 dB ii 110 dB?
b Draw a bar chart to compare the percentages of hearing loss which had been suffered by ages 20 and 50. Think of a way of showing all three noise levels on your chart.
c What do you conclude from the graph:
i about someone who has worked in a noisy environment for a long time
ii about the connection between noise level and hearing?
[ knowledge, considering, numeracy ]
8Le5 Sound wordsearch
Q
R
N
L
S
V
W
T
Y
U
H
I
X
Z
O
M
J
K
G
Answer the questions below, and then find your answers in the wordsearch.
1 The ears do this. _____________
2 A reflection of sound. _____________
3 Move backwards and forwards. _____________
4 The unit for loudness. _____________
5 Materials which stop sound reflections do this. _____________
6 The number of vibrations every second. _____________
7 Sound can't travel through this. _____________
8 Sound can be heard through a _____________ , liquid or gas.
9 This travels slower than lightning during a storm. _____________
10 A low pitch note has a _____________ frequency.
11 Unit for frequency. _____________
12 This causes an echo. _____________
13 The tube that sound waves travel along to get to the eardrum. _____________
14 The _____________ nerve carries impulses to the brain.
15 This part of the ear changes sound energy into electrical energy. _____________
8Le6 Ear protectors
Noise can be a big problem in industry. When working in noisy places many workers wear ear protectors.
Type of ear protector
Reduces noise levels by
Disadvantage
A Cotton wool plug
10 dB
Works loose, needs clean hands to replace
B Greased cotton wool plug
30 dB
Works loose, needs clean hands to replace, could cause irritation
C Polystyrene ear plug
Can be uncomfortable as it fits tightly in the ear, causes sweating, needs clean hands to fit
D Ear muffs containing sound absorbing materials such as foam, attached to a helmet
40 dB
Can be uncomfortable as it covers the ear, causes sweating, not as well fitting as the headband type.
E Ear muffs containing sound absorbing material such as foam, attached to a head band
50 dB
Can be uncomfortable as it covers the ear, causes sweating
1 Which ear protectors:
a would be best to use in a noisy work environment? Why?
b reduce noise levels by the same amount?
c are likely to work loose?
d can be uncomfortable?
e give the least protection?
f need clean hands? Explain why clean hands are needed?
2 Trapped air is a good sound insulator. Which of the ear protectors above have trapped air in them?
3 Soft materials absorb sound. Which of the ear protectors above have soft materials in them?
4 Why is wearing ear protectors attached to a helmet the most suitable method on a building site?
[ knowledge, considering ]
8L Summary Sheets
Sound and hearing
Sound vibrations and waves
Sound is a form of energy. Sounds are made when things vibrate. The vibrations are passed on by particles in solids, liquids or gases. Sound needs a substance to pass on the vibrations, so it can travel through solids, liquids and gases but not through a vacuum.
The speed of sound is faster through solids than liquids, and slowest through gases. This is because the particles are very close together in solids and so the energy is more likely to be passed from one particle to the next. The sound travels in all directions because the particles move in all directions unless something stops them.
Sound waves can be shown on an oscilloscope.
The frequency of a wave is the number of vibrations each second. The unit for frequency is hertz (Hz). If you listen to a sound with a frequency of 100 Hz, one hundred waves reach your ear every second. High pitched sounds have a high frequency, and low pitched sounds have a low frequency.
The distance between the waves is called the wavelength. It can be measured between any point on a wave and the same point of the next wave. It is often more convenient to measure it between the top of one wave and the next.
Half the height of the wave is called the amplitude. The loudness of a sound depends on the amplitude. Louder notes have more energy and the wave has a bigger amplitude.
Hearing and the ear
Sound waves travel through the air and into the ear. They cause the eardrum to vibrate. The vibrations are passed on to the cochlea in the inner ear, where they are changed to electrical signals called impulses. A nerve takes this message to the brain. When the message reaches the brain we hear the sound.
Sound can damage the ears if it is too loud or goes on for too long. Loud sounds can damage the eardrum or the cochlea. Unpleasant sound is often called noise.
We can measure how loud a sound is by using a sound intensity meter. This is an instrument which measures the loudness of a sound in decibels (dB). The threshold of hearing is the quietest sound we can hear and we say this is 0 dB.
Soft materials can absorb sound. Soft materials are used in soundproofing and for making ear protectors. Double glazed windows and soft materials like curtains help to reduce sound levels.
Sound and light
One major difference between light and sound energy is that light can travel through space (a vacuum) but sound cannot.
Light also travels much faster than sound. It is nearly a million times faster. Light travels at 300 million metres per second (or 300 000 km/s) and sound travels at about 330 metres per second.
Both light waves and sound waves can be reflected. We hear a reflected sound wave as an echo.
8L Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
8La
1
Know what causes sound.
Know that sounds can be loud or soft.
3
Know that sounds can be high or low.
4
Know how sound travels.
8Lb
Know what pitch is.
Know what frequency means.
Know the relationship between amplitude and loudness.
Know how to describe sound waves.
8Lc
Know the differences between light and sound.
Know what sound can and cannot travel through.
Know which things sound travels through the quickest.
Know how the particle model explains how sound travels.
8Ld
Know about the energy change that happens in the ear.
Know what the different parts of the ear do.
Know how the brain allows us to hear.
Know some causes of deafness.
8Le
Know how the loudness of a sound can be measured.
Know the unit for measuring the loudness of a sound.
Know how sound can damage the ears.
Know some ways of soundproofing.
8L Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
8La - Sound advice
Word
Pronunciation
Meaning
intensity
The loudness or volume of a sound.
pitch
How high or low a note sounds.
vibrate
Move backwards and forwards.
8Lb - Music to your ears
amplitude
Half the height of a wave.
frequency
free-kwen-see
The number of waves each second.
hertz (Hz)
The unit for frequency. 1 hertz means one wave per second.
loudness
How loud a sound is; the volume of a sound.
oscilloscope
oss-ill-O-skope
An instrument which shows a picture of a wave on a screen.
wave
A way of transferring energy. Waves can be side to side or backwards and forwards movements.
wavelength
The distance between the top of one wave and the top of the next.
8Lc - Sound travelling light
vacuum
A completely empty space with no particles.
8Ld - 'ear 'ear
cochlea
cok-lee-a
The part of the ear that changes vibrations into electrical impulses.
eardrum
A thin membrane inside the ear which vibrates when sound reaches it.
impulse
Electrical signal carried by a nerve cell.
8Le - Annoyed by noise
decibel (dB)
dess-i-bell
Unit for measuring the loudness of a sound.
noise
Unpleasant sound.
sound intensity meter
A meter which measures the loudness of a sound.
threshold of hearing
The quietest sound that can be heard.