Gill
Science
Stage 5
S
Waves
Part 1 Waves carry energy
S 43932
Number: 43932
Title: Waves
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material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Extract from Science Syllabus Years 7-10 © Board of Studies, NSW 2004
Photograph of a man standing on a cliff © Rhonda Caddy
Photograph of Satellite dish ©Nova Development Corporation (Art Exploision)
Unit overview pp iii-vi
Part 2 p 11
Front cover and all part
covers 1-4 inclusive
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Contents – Part 1
Lesson 1 – Energy revision .............................................. 3
Energy transformation examples..............................................5
Law of conservation of energy .................................................6
Energy transfer..........................................................................6
What did you achieve? .............................................................6
Lesson 2 – Listening to sound waves ............................... 7
What did you achieve? ...........................................................10
Lesson 3 – Sound: energy, vibrations and waves .......... 11
Sound as energy .....................................................................11
What makes sound vibrations? ..............................................13
Why do sound waves need a medium for propagation?.......15
What did you achieve? ...........................................................16
Lesson 4 – Types of waves ............................................ 17
Waves in ropes and springs ...................................................17
Water waves............................................................................19
Sound waves...........................................................................21
Electromagnetic waves...........................................................24
What did you achieve? ...........................................................25
Lesson 5 – Describing and visualising waves................. 27
Oscilloscopes ..........................................................................31
What did you achieve? ...........................................................36
Suggested answers – Part 1........................................... 37
Exercises – Part 1 .......................................................... 41
Part 1
Waves carry energy
1
2
Waves
Lesson 1 – Energy revision
This activity is a pretest. It is a quick test to check what you know before
you begin the unit. If you find the test easy, you are ready to begin
learning about waves as energy carriers. If you don’t know some of the
answers don’t panic the suggested answers will remind you of the
concept.
Activity: Pretest
Circle the best alternative for questions 1 to 4 below.
1
What is energy?
a how heavy something is
b the ability to make things move or change
c the amount of space something occupies
d how a machine runs
2
What is matter?
a
b
c
d
Part 1
things, such as substances or objects
something you can see
something you can feel or touch
energy
3
Which statement is true?
a Energy and matter are the same as each other.
b Everything has the same amount of energy.
c Only moving things have energy.
d Energy can change from one type to another.
4
Which statement is not true?
a Light energy can travel from the Sun to Earth.
b Sound energy can travel from the Sun to Earth.
c A spaceship moving from Earth towards the Sun has kinetic energy.
d A rocket contains potential energy to let it blast off from Earth
towards the Sun.
Waves carry energy
3
5
There are several different types of energy. Tick the examples
below that are types of energy.
heat, such as the heat from a fire
light, such as the light from the Sun
sound, such as the noise from an explosion
chemical, such as the energy stored inside food
nuclear, such as the energy released by a nuclear reactor
electrical, such as the energy used to run a television
potential, such as the energy stored in an object lifted up against
gravity
potential, such as the energy stored in an object bent, stretched or
compressed
kinetic, such as the energy in the moving parts of a motor.
6
How can energy move from one place to another? Use the names of
some of the types of energy to complete these sentences.
a
_______________ energy travels through matter that is a
conductor. Sometimes it jumps between conductors as large
sparks.
b
_______________ energy does not need matter to travel.
It can pass through matter that is transparent.
c
_______________ energy can only move through matter.
It cannot pass through a vacuum. (A vacuum is a space that
does not contain any matter.)
d
_______________ energy is another type of energy that can
move through matter and through a vacuum.
Check your responses by going to the suggested answers section.
Now consider some examples of energy transformation where energy
changes from one form to another.
4
Waves
Energy transformation examples
Part 1
1
Chemical energy in fireworks can be transformed quickly into heat,
light and sound energy.
2
Lifting an elephant against gravity requires energy which is
transformed into increasing elephant’s potential energy. If the
elephant falls its potential energy changes to kinetic energy.
3
A bent ruler can change potential energy to kinetic energy.
Waves carry energy
5
Law of conservation of energy
One of the most important ideas in science is conservation of energy.
By about 1850 scientists became aware that if a certain type of energy
disappeared, other types of energy appeared. It became accepted that energy
was preserved or saved. Energy could not be created or destroyed. Energy
just changes from one form to another (transformation) or is transferred to
another location. The total amount of energy does not change.
Repeated observations and/or measurements give results that support this
idea. Thus the idea of conservation of energy is reliable. This idea is also
found to apply with very small objects like atoms, human-sized objects or
objects as large as stars and galaxies. It applies universally, that is,
throughout the known Universe. An idea like this, that is universally reliable,
is called a law.
Energy transfer
Energy transfer is different from energy transformation. Energy transfer
is when energy moves from one location to another. Examples are:
•
heat energy transferring out of your hand on touching cold metal
•
heat from a fire warming a room.
Go to the exercises section and complete Exercise 1.1: Revision of
energy concepts.
What did you achieve?
Tick what you can do:
describe the difference between matter and energy
identify different types of energy
distinguish between transformation, transfer and conservation of
energy.
6
Waves
Lesson 2 – Listening to sound
waves
Sound energy is carried away from its source, the place where it is
released, by sound waves.
Sound waves need a medium for propagation. This mean that sound
waves need to travel through matter.
Sound waves from explosions on the Sun’s surface cannot reach the
Earth. There is just empty space and no matter between the Sun and the
Earth. Here on Earth there is usually gas (air), liquid (water) or a solid
between your ears and any source of sound. Sound waves can propagate
through the matter that surrounds your ears.
Listen to the audiofile Fifteen different sounds at
http://www.cli.nsw.edu.au/Kto12 and follow the links to Stage 5 Junior
Science, Year 9, Waves, Lesson 2.
Activity: Observations and inferences
Observations are what you detect using your senses – sight, hearing,
touch, smell and taste.
Inferences are different. An inference comes after an observation. An
inference is what you think happened. It is based on what you observed
and information that you have stored in your brain from past experience.
When you hear a sound you are making an observation. Only then can
you make an inference. The inference is what you think happened based
on observations, knowledge and understanding from past experiences.
Listen to the people on the audiofile as they explain the activities that you
are going to do. If you do not have access to a computer with Internet
connections, then complete the I can’t listen section at the end of this
lesson.
Part 1
Waves carry energy
7
There are fifteen different sounds on the audiofile. Observe (listen to)
each sound then make an inference; write down what you think is the
source of the sound.
1
_______________________________________________________
2
_______________________________________________________
3
_______________________________________________________
4
_______________________________________________________
5
_______________________________________________________
6
_______________________________________________________
7
_______________________________________________________
8
_______________________________________________________
9
_______________________________________________________
10 _______________________________________________________
11 _______________________________________________________
12 _______________________________________________________
13 _______________________________________________________
14 _______________________________________________________
15 _______________________________________________________
Listen to the sounds again to check your inferences.
Check your response by going to the suggested answers section.
Now, test how good you are at distinguishing intermingled sounds.
8
Waves
Listen to the audiofile People laughing at http://www.cli.nsw.edu.au/Kto12
and follow the links to Stage 5 Junior Science, Year 9, Waves, Lesson 2.
Activity: How many people can you hear?
How many different voices can you hear? How many people are there?
___________________________________________________________
Check your response by going to the suggested answers section.
What parts of your body are involved in hearing? Use books or a
computer to find out. If you are connected to the Internet go to
www.lmpc.edu.au/science, for some links. What you find out can be
used to complete Exercise 1.2: Labelling parts involved in human
hearing.
I can’t listen
If you cannot listen to the audiofile, here is a listening activity for you.
Activity: I can’t listen
1
Listen! Write down five things that you can hear.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
Part 1
Waves carry energy
9
2
Now keep listening. Try to write down another five sounds that you
can hear.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
3
Turn on the television or radio for two minutes only. Listen but
don’t watch!
In the two minutes that you are listening, how many different voices
do you hear?
_______________________________________________________
Go to the exercises section and complete Exercise 1.2: Labelling parts
involved in human hearing.
What did you achieve?
Tick what you can do.
describe sound energy as a form of energy which requires a
medium for propogation
identify sounds on an audiofile (or made in your surroundings)
distinguish between the sound of different people’s voices
identify parts involved in human hearing on a diagram.
10
Waves
Lesson 3 – Sound: energy,
vibrations and waves
All sound is produced as a result of particles vibrating. Vibrating
particles have energy.
Sound as energy
All forms of energy are able to cause objects to move.
Activity: Sound energy produces movement
Try this activity to see how sound energy produces movement.
What you will need:
• a balloon
What to do:
1 Blow up the balloon. Hold the neck of the balloon firmly between
two fingers so that the air cannot escape. Put your other hand on the
other end of the balloon.
Part 1
Waves carry energy
11
2
Now talk to your balloon! Go on. No-one is watching!
What did you feel with your hands?
_______________________________________________________
You probably felt shaking or vibration.
3
Now tie off the end of the balloon. Hold the balloon between the
sensitive tips of the fingers of both hands.
Talk quietly, talk loudly and sing to your balloon. What do you
observe with vibrations in the balloon when you put more energy
into your talking or singing?
_______________________________________________________
The more energy that you put into talking or singing, the more sound
vibration you detect in the balloon. Sound energy from your voice made
the balloon vibrate.
12
Waves
What makes sound vibrations?
Activity: What makes sound vibrations?
Try this activity to help you understand the movements in a vibration.
You will need:
•
a ruler – a flexible plastic one is best.
What to do:
Hold the ruler so that about 7 cm of it is on a table and the rest sticks out
off the table. Press down firmly so that the end of the ruler on the table
does not move. Then flick the other end of the ruler so that it vibrates.
Watch carefully to see the way that the ruler moves. What does it do?
___________________________________________________________
___________________________________________________________
___________________________________________________________
Did you notice that the ruler bounces up and down? You only flicked it once
but it kept going up and down for quite some time.
The vibrations of the ruler are similar to the movements of a swing.
But it’s easier to see what a swing does because it doesn’t move so
quickly!
Part 1
Waves carry energy
13
position
speed
acceleration
negative
maximum
zero
positive
maximum
zero
maximum
zero
maximum
zero
maximum
A swing hangs in the middle. To start the swing, you pull it backwards.
Then it goes to the middle, forward, to the middle and back, middle,
forward, middle and back, middle, forward, middle and back … and if
you don’t do anything, it eventually stops in the middle again.
That’s what the ruler was doing, but up and down. And that is what the
balloon was doing between your finger tips, vibrating in and out.
Vibrations can also cause sound. When a window shakes backward and
forwards it makes a rattling sound. Place your finger tips on the middle
of the front of your neck and make sounds. You should be able to feel
the vibrations in your voice box that produce sounds.
Energy, vibrations and sound go together.
Go to the exercises section and complete Exercise 1.3: Vibration and
sound. This exercise lets you plan and carry out a demonstration to show
that vibrations can produce sound waves.
14
Waves
Why do sound waves need a
medium for propagation?
Sound energy travels as sound waves. Sound waves are carriers of sound
energy. So, what do sound waves need to travel?
Think about when sound waves
cannot travel.
It is silent out in space because
sound waves cannot travel
through a vacuum. There must
be matter, or substances, for
sound to travel.
Sound waves can travel
through solids, liquids and
gases because these things are
matter.
Why is matter needed?
Sound waves move by making matter vibrate. So if there is no matter to
vibrate, the sound wave cannot be passed on and the sound energy cannot
travel.
A reminder about solids, liquids and gases
What are solids, liquids and gases like?
In solids, particles are
packed closely together.
In gases, particles are
spaced widely apart.
In liquids, particles are
neither very close or wide
apart.
These ideas are part of what is called the particle model/theory of matter.
Some scientists say that this is the most important model or theory used
in science.
Part 1
Waves carry energy
15
How are solids, liquids and gases alike?
__________________________________________________________
Did you say that they all contain particles? Anything that is matter is made up
of particles. Particles are needed for sound energy to travel.
Sound waves are able to travel most quickly through solids because the
particles are very close together. Movement in one particle transfers
quickly to the particles next to it. Sound waves travel most slowly
through gases since the particles are further apart.
What did you achieve?
Tick what you can do.
show that sound is a form of energy able to produce movement
demonstrate how a vibration produces sound
plan and perform an activity to show that vibration produces
sound waves
explain why sound waves can travel through matter but not
through a vacuum.
Look at the list again. If you haven’t ticked all the statements, go back
and review the sections where you are not confident. Then, tick the
items that you have revised in the check list above.
16
Waves
Lesson 4 – Types of waves
Waves can be of two main types. These are described according to how
the motion of the particles or field direction changes compared to the
direction in which the wave travels. The activities below will clarify this
classification.
Waves in ropes and springs
Activity: Making waves in a rope
What you will need:
•
a rope or thick cord. It doesn’t matter how long it is, provided it can
wiggle like a snake.
What to do:
1
Pull the rope into a straight line.
2
Hold one end of the rope just above the ground and wiggle it from
side to side. It probably needs to move about 30 cm each way, going
across and back each second.
3
Sketch the shape the rope makes, below.
4
Where does the energy come from to make the wave shape in the
rope?
_______________________________________________________
Part 1
Waves carry energy
17
5
Make the rope straight again. This time, move it across and back
once only. What do you notice?
_______________________________________________________
Look at the answers in the answer pages before you continue.
The waves in a rope moved from side to side are called transverse
waves. Transverse means in a crosswise direction. The rope moves
across the direction the waves travel. As you move the rope from side to
side the waves travel away from you, the source of the waves.
Activity: Making waves in a slinky spring
This activity requires a slinky spring. (Any coiled spring that you can
compress, or squeeze together, with your fingers will do.) If you cannot
get a suitable spring read through the activity then do step 3.
What you will need:
•
a slinky spring
What to do:
1
Lie the slinky in a straight line. It will look like this:
2
Squeeze together the first few rings. Then let the rings go. What do
you observe?
_______________________________________________________
_______________________________________________________
The energy you put into the spring when you compressed the rings is
carried along the spring as a wave.
18
Waves
3
Here is a problem you can do, even if you do not have a slinky.
The diagram below shows a spring with a compression, or place
where it is compressed. The next three diagrams show the wave
moving along the spring but the diagrams are not in the correct
order. Number them in sequence from 2 to 4.
1
The wave moves from right to left, so the numbers are 1, 2, 4 and 3.
The waves in the spring moved along the direction that the waves travel.
Waves which move along the direction that the waves travel are called
longitudinal waves.
Water waves
If you’ve been in a boat on waves, then you know the feel of waves
going up and down. They make a pattern like the pattern of waves in a
rope. Ocean water waves produce movement up and down across the
direction the waves are travelling. They can be called transverse waves.
Part 1
Waves carry energy
19
Activity: Drawing water waves from above
What you will need:
•
a dish, tray or sink that will hold water
•
an eye-dropper
•
a cup
•
some food colouring or water paint.
What to do:
1
Fill the dish with water. Add some food colouring to make the water
coloured. The colour makes patterns on top of the water easier to
see. Let the water sit until its surface is smooth.
2
Put extra water into the cup and draw some up into the eye dropper.
Drop one drop of water into the middle of the tray of water.
3
What do you see? Let the water settle, then add another drop. What
pattern forms?
Draw the pattern on the sketch below.
tray of water
drop of water here
Did you notice that circles formed around the point where you dropped
the water? These circles got bigger and bigger as they moved outwards
on the tray.
20
Waves
tray of water
drop of water here
ripples in the water
Sound waves
Sound waves are easy waves to detect, make and think about. You have
your own built-in sound detectors—ears —and your own sound sources
such as your voice box or clapping hands.
Similar ways are used to describe or draw the different kinds of waves.
So what you learn about sound waves will help you to understand other
kinds of waves as well.
Learning about other kinds of waves will also help you understand more
about sound waves. For example, the diagram you used to show water
waves can help you to picture sound waves.
tray of water
drop of water here
ripples in the water
Part 1
Waves carry energy
21
How is this pattern like sound waves?
The drop of water was added to one place. The energy in the push from
the drop spreads out in all directions over the water in the tray.
In a similar way sound starts in one place, the source, and spreads out in
all directions. You can hear someone speaking whether you are in front
of them or behind them or even above or below them.
Sound energy moves in waves even though we cannot see sound waves
moving through matter. When a drawing showing sound waves is made,
it often looks like the water waves in the dish above. The lines represent
sound energy moving out in waves from the central source. But
remember, the sound waves actually travel in three dimensions, not just
the two dimensions shown in a drawing.
Activity: Different ways of drawing sound waves
1
Draw lines onto the diagram below to show the sound of a dog’s
bark travelling outwards.
The lines in a diagram of sound waves can be replaced by series of
dots.
22
Waves
The dots in this diagram represent particles in the air. This reminds
you that sound is only transmitted through the particles that make up
matter.
Spaces where particles are drawn close together are compressions,
whereas spaces with few particles are rarefactions. A sound wave
is sometimes described as a compression wave because it is made up
of compressions separated by rarefactions.
2
On the diagram above, label a compression and a rarefaction.
Another way of showing compressions and rarefactions uses lines:
| | | |
|
|
| | | |
|
|
| | | |
|
|
|
Label a compression and a rarefaction on the diagram above.
3
Here is a summary to complete about sound waves:
Sound energy travels through _______________ as sound waves.
It travels at ____________ speeds in different kinds of matter.
__________________ sound wave consists of compressions, where
__________________ are close together, and ______________
where particles are ______________ widely apart.
Sound spreads out _____________ all directions from the _______ ,
where the sound is _____________ .
Part 1
Waves carry energy
23
Please turn to the answer pages to check your diagram and summary.
Electromagnetic waves
Electromagnetic waves are a group of waves that can be difficult to
imagine. They are different from all the waves you have learned about
so far, because electromagnetic waves do not need a medium to travel
through. Electromagnetic waves can travel though space and through
some kinds of matter. Your body has the ability to detect:
•
•
•
electromagnetic light waves with eyes
electromagnetic infra-red (heat rays) with skin heating up
electromagnetic ultraviolet with skin tanning.
These waves are called electromagnetic because they are made up of
changing electric and magnetic fields. Some examples of
electromagnetic waves are light, heat rays, X-rays and radio waves.
Activity: Transmitters of electromagnetic waves
Think of some substances that the types of electromagnetic waves below
can travel though.
a
light __________________________________________________
b
X-rays ________________________________________________
c
radio waves ____________________________________________
d
heat rays _______________________________________________
There are some suggestions in the answer pages.
24
Waves
When we draw electromagnetic waves, they are usually shown like a
wave in a rope, as:
Any wave of this shape is called a sine wave.
All kinds of electromagnetic waves travel very quickly. Through a
vacuum they all travel at 300 000 000 metres per second (3 x 108 ms–1).
Like all other waves, electromagnetic waves are a way that energy moves
from one place to another.
Go to the exercises section and complete Exercise 1.4: Waves as carriers
of energy.
What did you achieve?
Tick what you can do.
list different kinds of waves, such as waves in ropes, waves in
springs, water waves, electromagnetic waves and sound waves
draw or describe different kinds of waves
use the concept that waves are carrier of energy.
Part 1
Waves carry energy
25
26
Waves
Lesson 5 – Describing and
visualising waves
There are many types of waves—sound, water, electromagnetic waves
like light as well as earthquake waves—covered in your course.
Waves can be drawn in a number of ways. Here is a selection:
1
Waves produced by moving a rope up and down
direction waveform moves
direction of
initial
vibration
2
Waves close to a source, near the source and far from the
source
point source
Part 1
rest position of rope
Waves carry energy
spherical wavefront
plane wavefront
near source
far from source
27
3
Waves produced by dropping a cork in water
cork dropped here
Top view
Front view
28
Waves
4
Wave crests (high points) and troughs (low points) drawn
as wavefronts
flow of energy
wavefronts
5
Waves shown as wavefronts and a ray drawn in the wave
direction
direction
of wave
The most common representation of a wave is as a sine curve:
wavelength
Part 1
Waves carry energy
29
The wavelength of the wave is the distance between two consecutive
crests (high points), two consecutive troughs (low points) or any two
consecutive corresponding points. Corresponding points are points at the
same position on the wave.
Activity: Measuring wavelength of waves
Use a ruler to measure the wavelength of these waves to the nearest
millimetre
1
wavelength
_____ mm
2
_____ mm
3
_____ mm
Check your answers in the answer pages.
30
Waves
Compare the two waves in the diagrams below.
Use a ruler to confirm that the two diagrams have the same wavelength.
However, the two waves differ in their amplitude. Amplitude is the
maximum distance from the central position. Check that the crest and
trough in the first wave are 18 mm from the central position in the first
diagram and 10 mm from the central position in the second diagram.
If these diagrams represented waves in ropes the first would require you
to move your hand up and down most and would carry the most energy.
If sound waves, the first would be louder than the second. The first
would carry more energy and move your eardrum the most. If water
waves, the first would move more sand on the beach than the second.
Oscilloscopes
An oscilloscope is a device that helps you visualise waves.
You have probably already seen oscilloscopes in hospitals or in movies
or on TV. They are used to give a visual image of the beating of a heart,
breathing or blood pressure of a patient.
First some of the wave energy needs to be changed into electrical energy.
Sound wave energy entering a microphone, light energy entering a
photoelectric cell and kinetic energy (from movement or pressure)
entering a transducer can all send electrical energy to an oscilloscope.
You can obtain free software over the Internet that turns your computer
into an oscilloscope. Some websites enable you to simulate the operation
of a cathode ray oscilloscope (CRO) on your computer screen. Go to
<http://www.cli.nsw.edu.au/Kto12>
Select Science, then Stage 5 Junior Science and follow the links to
resources for this unit, Waves.
Part 1
Waves carry energy
31
The oscilloscope
changes electrical
energy into light
energy on a small
screen.
The screen is at the
end of a cathode ray
tube. The
oscilloscope is often
called a cathode ray
oscilloscope or CRO.
(pronounced the same
way as the word
crow, a type of bird).
The pattern of the
sound wave’s image
on the oscilloscope
screen is called a
wave trace. The
wave trace on this
oscilloscope screen is
an example of a sine
wave.
Oscilloscope
This is the wave trace for a loud sound.
And this is the wave trace for a soft sound.
Both of these waves have the same wavelength. The sound waves only
differ from each other in loudness heard and amplitude seen on the CRO.
32
Waves
How is the wave trace of a loud sound different from the wave trace of a
soft sound?
___________________________________________________________
___________________________________________________________
The loud sound makes a taller wave trace than the soft sound. A more scientific
answer would say that the loud sound produces a wave with larger amplitude.
Look at the drawing of an oscilloscope screen below.
Notice that the screen has a line through the centre of the wave trace.
Scientists measure the largest distance that any part of the wave trace can
be away from this middle line.
Using your ruler, measure the largest distance that the wave trace on this
oscilloscope is above the middle line. Measure in millimetres.
___________________________________________________________
The largest distance of the wave trace above the middle line is 14 mm.
Now measure the largest distance that the wave trace goes below the
middle line.
___________________________________________________________
The largest distance of the wave trace below the middle line is 14 mm.
Here are wave traces of the loud sound and the soft sound that you
considered previously.
Part 1
Waves carry energy
33
Loud sound
Soft sound
Which sound has more energy? ________________________________
What is the amplitude of the loud sound? ________________________
What is the amplitude of the soft sound? _________________________
Which sound has the larger amplitude? __________________________
The loud sound has more energy. The loud sound has the larger amplitude (19
mm). The soft sound has less energy and a smaller amplitude (10 mm).
How can you tell the amount of energy in a sound from its wave trace?
__________________________________________________________
__________________________________________________________
The amplitude of a wave trace gives you information about the amount of
energy. A sound with lots of energy has a larger amplitude whereas a sound
with a smaller amount of energy has a smaller amplitude.
34
Waves
Activity: Interpreting amplitude on a CRO
Here are the wave traces for three sounds, all with the same wavelength.
a
b
c
1
What is the amplitude of wave trace a? _______________________
2
What is the amplitude of wave trace b? _______________________
3
What is the amplitude of wave trace c? _______________________
4
Which sound has the smallest amplitude? _____________________
5
Which sound has the most loudness? ________________________
6
Which sound has the least energy? __________________________
Check your answers in the answer pages.
Go to the exercises section and complete Exercise 1.5: Comparing CRO
wave traces.
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35
What did you achieve?
Tick what you can do.
identify different ways of drawing waves
describe how a CRO helps you visualise amplitude and
wavelength of a wave.
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Waves
Suggested answers – Part 1
Check your responses against these suggested answers.
Activity: Pretest
1
b
2
a
3
d
4
b
5
They are all types of energy!
6
The answers, in order, are electrical, light, sound and heat.
Activity: Observations and inferences
1
an orchestra tuning up
2
a heart beat (of a baby)
3
a door bell
4
eating breakfast cereal
5
a car starting and driving off
6
a gong
7
kids on a roller coaster
8
jumping into a pool
9
a basketball game
10 pigs
11 seagulls
12 brushing teeth
13 an electric typewriter
14 a zipper going up and down
15 turkeys!
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Waves carry energy
37
Activity: How many people can you hear?
There were actually ten people laughing! Did you think that there were that
many different voices?
Activity: Making waves in a rope
3
4
The energy came from the kinetic energy of your hand. (This kinetic
energy came from chemical energy stored in your muscles. That chemical
energy came from chemical energy in food which was formed from light
energy by photosynthesis in plants. That light energy came from nuclear
energy in the Sun).
5
A single wave ‘bump’ moves along the rope. It looks the same and travels
at the same speed all the way along the rope.
Activity: Different ways of drawing sound waves
1
Remember sound spreads out in all directions from the dog.
compression
rarefaction
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Waves
2
3
compression
rarefaction
Your summary below may not have exactly the same words, but it should
have the same meaning.
Sound energy travels through matter as sound waves. It travels at different
speeds in different kinds of matter.
A sound wave consists of compressions, where particles are close together,
and rarefactions where particles are spaced widely apart.
Sound spreads out in all directions from the source, where the sound is
made.
Activity: Transmitters of electromagnetic waves
a
air, water, glass, transparent materials, vacuum
b
human body, luggage at airports, most materials
c
air, water, vacuum of space, non-metallic materials
d
air, water, vacuum of space.
Activity: Measuring wavelength of waves
Your answers should be the same as or differ by only 1 mm from the answers
below:
1
16 mm
2
10 mm
3
26 mm.
Activity: Interpreting amplitude on a CRO
Part 1
1
21 mm
2
28 mm
3
15 mm
4
c
5
b
6
c
Waves carry energy
39
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Waves
Exercises – Part 1
Exercises 1.1 to 1.5
Name
____________________________
Teacher _________________________
Exercise 1.1
1
Revision of energy concepts
Distinguish between matter and energy.
_______________________________________________________
_______________________________________________________
_______________________________________________________
2
Distinguish between energy transformation and energy transfer.
_______________________________________________________
_______________________________________________________
_______________________________________________________
3
Explain why the idea of conservation of energy is called a law in
science.
_______________________________________________________
_______________________________________________________
_______________________________________________________
Part 1
Waves carry energy
41
Exercise 1.2 Labelling parts involved in human hearing
42
1
Label the auditory canal, ear and eardrum of the outer ear:
2
Label the stirrup bone (smallest bone in the human body) of the middle
ear, cochlea of the inner ear and the auditory nerve connected to the brain.
Waves
Exercise 1.3
1
Vibrations and sound
Why is sound considered a type of energy?
_______________________________________________________
_______________________________________________________
_______________________________________________________
2
What evidence is there that sound is produced by vibrations?
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
3
Use a rubber band to demonstrate that vibration can produce sound
waves.
Write sentences to outline (that is, indicate the main features of) the
activity you perform. The sentences can be arranged as numbered
steps like this:
1
2
3
or as bullet points like this:
•
•
•
Try to write a clear outline so that another person of your age, given
a rubber band and your outline, could also perform the activity.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
Part 1
Waves carry energy
43
Exercise 1.4
1
Waves as carriers of energy
An earthquake in South America can produce waves in Sydney
Harbour. Explain how the energy from the earthquake is transferred
to Sydney Harbour.
_______________________________________________________
_______________________________________________________
2
A storm with strong winds near New Zealand can produce three or
four metre waves on the east coast of Australia. Explain how the
energy is transferred from New Zealand to Australia.
_______________________________________________________
_______________________________________________________
3
The energy that keeps you alive and moving originally came from
the Sun. Explain how waves carried this energy that keeps you alive
on Earth from the Sun.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
4
Explain how nuclear energy released in the Sun enables you to make
sound waves with your voice box.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
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Waves
Exercise 1.5 Comparing CRO wave traces
Here are the wave traces for four sounds that are travelling through
water.
H
I
J
K
1
What is the amplitude of sound H? __________________________
2
Which sounds have the same loudness? ______________________
3
Which sounds have the same wavelength? ____________________
4
What is the wavelength of sound H? _________________________
5
Which sound has the lowest frequency? ______________________
6
Which sounds have the same frequency? _____________________
7
Compare sound H with sound I. ____________________________
_______________________________________________________
8
Compare sound I with sound J. ______________________________
_______________________________________________________
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9
Could you draw a sound wave without an amplitude? Why or why not?
_______________________________________________________
_______________________________________________________
10 Sketch a wave trace for a sound that is
softer and higher than sound J. (A pale
outline of sound J is provided to help
you.)
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Waves