Australian Curriculum
7.4 Physical Science
1
CONTENTS
Student outcomes
3
Forces
4
Activity 1: Pushing and pulling forces
5
Activity 2: Describe a force
6
Activity 3: Only dummies collide
7
Activity 4: Stop!
10
Activity 5: Describing a force
12
Activity 6: Measuring forces
16
Assignment 1: Forces around you
18
Activity 7: Friction, a contact force
19
Activity 8: Does the type of surface affect friction?
20
Activity 9: Reducing friction
21
Activity 10: Increasing friction
22
Assignment 2: Friction
23
Assignment 3: Friction and bicycles
24
Open investigation
25
Mousetrap racers
28
Activity 11: Force due to gravity (a non-contact force)
29
How things work: simple machines
30
Activity 12: Levers
33
Activity 13: Wheel and axle
35
Activity 14: Inclined planes
36
Activity 15: Pulleys
38
Activity 16: Gears
40
THERE IS MORE THAN ENOUGH CONTENT FOR A TERM’S WORK SO YOUR
TEACHER WILL SELECT ACTIVITIES SO THAT ALL OUTCOMES CAN BE ACHIEVED.
THE MORE EFFICIENT YOUR CLASS IS – THE MORE ACTIVITIES YOU WILL BE ABLE TO DO!
This booklet was produced at Rossmoyne Senior High School to meet the needs of the
Australian Curriculum. September, 2013.
2
OUTCOMES
At the end of this unit you should have worked hard to achieve most of the outcomes
shown below:
1. Change to an object’s motion is caused by unbalanced forces acting on the object:
 investigating the effects of applying different forces to familiar objects such as

change of shape

change of size

change of speed/acceleration

change of temperature e.g. from compressing air in a bicycle pump
 investigating common situations where forces are balanced, such as stationary objects,
and unbalanced, such as falling objects
 investigating a simple machine such as lever or pulley system

identify effort arm and load arm of the lever system

investigate how changes in the position of the fulcrum i.e. relative lengths of the load
arm and effort arm change the effort required to lift a load

consider whether the lever system provides a force or distance/speed advantage
2. Earth’s gravity pulls objects towards the centre of the Earth:
 exploring how gravity affects objects on the surface of Earth

air resistance can slow an objects fall

in the absence of air resistance any two objects dropped from the same height will hit the
ground at the same time
 considering how gravity keeps planets in orbit around the sun

there is a force of attraction between any two objects

the larger the objects the stronger the force of attraction

the Moon remains in orbit around the Earth because of the Earth’s gravitational pull.

The planets orbit the Sun because of the gravitational pull of the Sun
3
WHAT IS PHYSICS?
Physics is the branch of science that studies energy and the particles that make up matter.
There are many branches of physics – mechanics of stationary and moving objects; heat;
light; sound; electricity and nuclear physics. By careful measuring, physicists aim to
understand the makeup of the natural world and try to explain natural phenomena like
rainbows and frostbite.
FORCES
FORCES AROUND YOU:
What gets a car or bike moving? Why does it then keep moving?
How do we stop it?
You already know, of course, that if you want something like a wheelbarrow to move you
need to push or pull it. We call this push or pull a FORCE.
Forces are also required to get a motor car moving or, in fact, to get any object moving.
Once this object is moving, the application of additional force is required to make the object
go faster or slower or to change the object's direction.
You also know from experience that it if you want to stop something that is moving, say a
heavily laden supermarket trolley, a push or a pull also has to be exerted or it will keep
rolling.
Thus, a force is also involved in stopping something that is moving.
A force, then, is something that can (or at least tries to) (i)
get an object moving;
(ii)
change the speed or direction of a moving object;
(iii)
stop a moving object.
4
ACTIVITY 1: PUSHING AND PULLING FORCES
Forces can act in different ways. Some act by pushing, and others act by pulling, an object.
1.1
Look at the pictures below. Some of the forces are pushing forces while some are
pulling forces. Copy and complete the table in your note books.
Forces which act by
pulling on an object
Forces which act by
pushing on an object
COPY INTO YOUR BOOK
2
1
4
3
5
6
7
8
9
10
5
ACTIVITY 2: DESCRIBE A FORCE
Forces are not things we can see or touch.
But it is often easy to tell when a force acting.
We can tell when a force is acting, by observing what it can do. We observe the effect it has
on things it acts against.
2.1 Some of the forces which act change the speed at which an object moves. Write down
some examples you know.
2.2 Some forces can change the shape of the things they act on.
Can you think of any?
The following activities may help you to answer the last two questions.
Firstly, let’s investigate forces which act when in contact with a surface.
We begin by posing the following questions:
Why do car seats have head restraints?
Why wear seat belts?
If a force is required to start something moving, you may wonder what would happen if a
force was suddenly applied to a vehicle.
FORCES get me
going, change my
speed and
direction, and
stop me.
6
Imagine, for example, that you are sitting in a stationary vehicle when a fast-moving vehicle
runs into the back of you.
Imagine further that your seat has no head restraint.
Let's investigate what would happen.
ACTIVITY 3: Only dummies collide!
You should work in a group for this activity.
Materials:








A wooden ramp similar to the one in the
diagram, about 1.5 m long and 30 cm
wide
Metre ruler
Cardboard carton or bricks stacked
about
40 cm high
Two trolleys
About 70 g of plasticine to make two
dummies
Matches
Powder
Procedure:
1.
Weigh the following amounts of plasticine to make a dummy.
Head 3.5 g
Chest and Arms 16.0 g
Legs 15.5 g
These masses are important so that the dummy is in the same proportion as an average
human body.
7
To make the head, mould the plasticine into a disc about the size of a ten cent coin. Put
this disc on your little finger and push down, all around. Remove the disc carefully and
gently squeeze in the bottom to make a hollow sphere. Use a matchstick to join the head to
the body. When it is finished, it should be approximately the same size as the diagram
below.
matchstick
2.
Repeat the above procedure to make a second dummy
3.
Put a dummy on the front of each trolley. You should powder each dummy
to reduce the stickiness.
4.
Mark 20-cm intervals on the ramp.
5.
Set up the materials with trolley 1 placed at the 100 cm mark on the ramp.
6. Place cart 2, 30-40 cm in front of the ramp, directly in line with trolley 1.
7. Release trolley 1 and watch what happens to the dummies.
8. Repeat steps 5, 6, and 7 three or four times and then answer the following questions.
Don't forget to make sure that you place the dummy at exactly the same place each
time.
REMEMBER!!
Write full sentence answers.
8
QUESTIONS:
1.
What happened to the dummy on trolley 1 during the collision?
Did it move towards the front of the car, the back of the trolley, or stay in the same
position?
2.
Try to explain why this happened.
3.
What happened to the dummy on trolley 2 during the collision?
Did it move towards the front of the trolley, the back of the trolley, or stay in the same
position?
4.
Try to explain why this happened.
Let's see how this can be applied to the road situation:
5.
What happens to the passengers in a stationary vehicle when it is hit from behind by
another car?
6.
What design feature of modern cars reduces the risks of serious injury from this type
of collision?
CHALLENGE QUESTIONS:
7.
Explain why the passengers standing in the aisle of a bus are forced towards the back
when it lurches forward on starting off.
8.
Why is it that in trucks there should always be a strong barrier between the load and
the driver’s cabin?
9
You have probably experienced this already while you have been riding your bike.
What happens when you are moving quickly and have to stop suddenly? What
happens if something gets jammed in your front wheel causing it to stop turning?
ACTIVITY 4: STOP!
Materials:
• A wooden ramp as in Activity 1
• Cardboard carton or stacked bricks
as in Activity 1
• Trolley as in Activity 1
• Plasticine dummy as in Activity 1
• Length of wood no more than 3 cm
high to act as a barrier
• Chalk
• Metre ruler
Procedure
1.
Again mark 20-cm intervals on the ramp. Set up the materials as in the
diagram.
2.
Put the dummy on the front of the trolley. Place the trolley at the 20cm mark.
Release the trolley.
3.
Watch what happens to the dummy. Use chalk to mark where the dummy finally
stops. Measure the distance from the chalk mark to the point on the front of the
barrier where the impact occurred. Measure to the nearest centimetre.
4.
Repeat steps 1 and 2 three or four times. Record the measurement each time. Find
the average distance for all the trials.
5.
Again place the dummy on the front of the trolley. Place the trolley at the 40 cm
mark and release it. Do this three or four times. Each time measure the distance
from where the dummy lands to the point on the front barrier where the impact
occurs. Again find the average distance and record it in your table.
6.
Repeat step 5 for each distance shown in the table.
10
Copy the following table into your book and record your results.
Position on ramp
where trolley
released from
(cm)
20
40
60
80
100
120
Trial 1
Trial 2
Trial 3
Average
Ask you teacher for some graph paper and plot the average distance the dummy
travelled (cm) against the trolley release position on the ramp (cm).
Average distance
travelled (cm)
7.
Distance dummy continued to travel (cm)
Trolley release position (cm)
HAVE A GO AT THESE QUESTIONS:
1.
Suppose the trolley was released from the 110 cm mark on the ramp. Use your graph
to predict how far the dummy would continue to travel.
2.
Draw a 110 cm mark on the ramp. Place the dummy on the trolley at this mark, and
release it. How far does the dummy continue to travel?
Do it 3 times and obtain the average.
3.
Was your prediction correct?
11
ACTIVITY 5: DESCRIBING A FORCE
This activity has five parts. Discuss with your teacher whether you will do all parts or
whether different groups will do different parts.
Aim: To experience a range of different forces.
Part A:
Materials: table tennis ball
Procedure:
1.
Use the table tennis ball to answer these questions.
a.
b.
c.
2.
What happens if you blow on the ball while it is moving towards you?
What happens if you blow on the ball while it is moving away from you?
What happens if you blow on the ball while it is moving across in front of you?
Play a game of blow ping pong. This game is played in groups of six, with three in
each team kneeling down on either side of a bench. The table tennis ball is placed or
dropped in the middle of the bench and you have to try to blow it over to the other
side. You can only change the motion of the ball by blowing. If it goes over the other
side or hits the arms or shoulders of the opposition a goal is scored.
Part B:
Materials:

washer about the size of a 20 cent coin

a piece of paper cut to the same diameter.
Procedure:
1. Hold the piece of paper in one hand and the washer in the other, at the same height.
2. Drop them both at the same time.
Questions:
1.
2.
3.
4.
5.
Write an inference to explain what happened. In your inference say what forces
were acting on the washer and the paper and in which direction they were
acting.
How did you know a force was acting on the objects?
Is this force pushing or pulling the objects?
What is the name of the special pulling force on both objects?
What is the name of the special pushing force on the paper?
12
Part C:
Materials: Plastic pen or ruler and a piece of paper.
Procedure:
1. Obtain a plastic pen or a plastic ruler and place it over some small pieces of paper
(about 0.5 cm2). Look carefully to see if the paper is attracted or repelled.
2. Rub the pen on your jumper or your hairy arm and pass the pen over the pieces of
paper again and observe any changes that occur. Do not put the rod directly on the
pieces of paper.
Questions:
1. Is there a force between the plastic and the paper
(a) before the plastic is rubbed?
(b) after the plastic has been rubbed?
2. How did you know that a force was acting?
3. Is the force a pushing force or a pulling force?
Part D:
Materials: 2 bar magnets, wooden stand, paper clip, cotton, sticky tape.
Procedure:
1. Set up a force system between the magnet and the paper clip
as shown in the diagram opposite, then answer the questions below.
Questions:
1.
2.
3.
4.
How do you know a force was acting?
What is this kind of force called?
Is the magnet in contact with the paper clip?
Is a push or pull force observed?
2. Hold one magnet in each hand. Feel what happens as you slowly bring the end of one
magnet close to the end of the other.
3. Repeat the test, but use the other end of one of the magnets.
Question:
4. Write a general comment describing the forces acting between the two magnets.
Part E:
Materials: bucket of water, golf ball, table tennis ball, rubber ball, styrofoam ball.
Procedure:
1. Put a table tennis ball into a bucket of water. Push it to the bottom of the bucket and
let it go.
2. Do the same with the other balls.
Questions:
1.
2.
What forces act on a ball in water? In which direction do they act?
Try to write a general rule about what happens to objects when they are placed
in water.
13
TYPES OF FORCES:
As you have seen in Activity 5, there are many different types of forces. Some forces act by
contact and are called contact forces. For example, when you push something by hand, or
pull it with a rope, you are using contact forces. Other examples are the wind blowing the
trees, ocean waves crashing on rocks, and the tiny forces holding a soap film together.
Some forces do not need contact, and can act at a distance. These are distance or noncontact forces. For example, two magnets exert a force on one another without touching.
Other examples of non-contact forces are gravity and electrical forces.
DIRECTION AND STRENGTH OF FORCES
Forces can act upwards, downwards, sideways or any direction at all. To show the
direction of a force you can use an arrow. You can then show the strength of the force by
the length of the arrow. A large arrow means a strong force and a small arrow means a
weak force.
BALANCED AND UNBALANCED FORCES
Consider a tug-of-war. Here there are
two equal forces acting in opposite
directions. There is no motion until
one force becomes greater than the
other.
14
Imagine you start to ride your bike along a flat road. To start off you use your muscles to
push on the pedals. This force then turns the back wheel resulting in a forward pushing
force. There are also frictional forces which tend to slow you down. There is friction
between the tyres and the road, between the moving parts of the bike, and between you and
the air.
Because the pushing forces are greater
than the frictional forces, the bike
speeds up. The forces are unbalanced
causing an increase in speed.
When you reach a constant speed the
forces are balanced, as shown.
If you stop pushing on the pedals, the
forces are again unbalanced and the bike
changes its motion by slowing down and
eventually stopping.
Even bodies which are not moving have forces acting on them (see figure below). Because
these forces are balanced the body stays where it is. It is only when the forces are
unbalanced that a change in motion or shape of the body occurs.
Road pushes
up on car
Gravity pulls
down on car
When opposing forces are unbalanced there is a change in speed (either speeding up
or slowing down) OR a change in shape.
When opposing forces are balanced no motion occurs OR the object keeps moving at
constant speed.
15
ACTIVITY 6: MEASURING FORCES
Materials:
 newton spring balance
 electronic mass balance
 bathroom scales
 plastic cup half full of sand
 wooden block
 six 50 g brass masses
If we want to measure a force we mostly use the property of elasticity. Some objects
stretch (become longer) or compress (become shorter) when a force is applied. After the
force is removed, they return to their starting shape and size.
A spring balance is one common way to measure a force. The force makes a spring inside
stretch. Outside, the amount of stretching is shown on a scale. A set of kitchen or
bathroom scales is often used to measure forces at home. Here a spring may be made to
squash (compress). Some schools have a force measurer that makes a hacksaw blade
bend. When the force is removed the blade becomes straight again.
Spring balance
Force measurer
Kitchen scales
UNITS OF FORCE
When we measure a force we need some units to measure it in. In science, the unit is the
newton (named after Sir Isaac Newton). The symbol for the newton is a capital N (without a
full stop after the N). For example, a force of 20 N is required to lift 2 kg of sugar.
IN SCIENCE THE TERMS WEIGHT AND MASS DO NOT MEAN THE SAME THING
Weight is a force - the downward pull of gravity on an object. It is measured in newtons
(N). E.g., a 14 year old girl might weigh 490 N and an apple about 1 N.
Mass is a measure of the amount of matter in an object. It is measured in kilograms (kg)
or grams (g). E.g. the mass of a 10 cent coin is 5 g.
Sometimes you may be asked the question: “How much do you weigh?” In everyday life we
often ‘weigh’ things in grams and kilograms. However, in science, mass and weight are
NOT the same. If someone says that they ‘weigh’ 45 kg, they have actually told you their
mass rather than their weight.
16
The way mass and weight differ in science is best seen when an astronaut goes to the
Moon. If he measured his mass he would find that it would not change. The amount of
matter in his body has stayed the same. If he measured his weight it would change by a
large amount. If he weighed 650 N on Earth, he would weigh only about 110 N on the
Moon! The reason for this is that the Moon is much smaller than the Earth. Its force of
attraction due to gravity is only about one-sixth that of Earth.
Procedure:
COPY AND COMPLETE THE TABLE BELOW.



Use a newton spring balance to measure weight.
Use an electronic mass balance to measure the mass.
Fill in the last column by calculating weight divided by mass.
OBJECT
WEIGHT (N)
Cup of sand
100 mL of water
Wooden block
Pencil case
Six brass weights
Homo sapien
MASS (kg)
Weight/mass
COPY INTO YOUR BOOK
QUESTION:
1.
Using mathematics how do you change a mass into a weight?
2.
Write down a mathematical formula for calculating weight if you are given the mass
of an object.
3.
Calculate the weight in newtons of the following:
(a)
(b)
(c)
(d)
(e)
4.
Toyota Corolla 1255 kg
20 cent coin 0.01 kg
loaf of bread 600 g
2 kg bag of sugar
house brick 4.1 kg
Calculate the mass of the following if a force of:
(a)
(b)
(c)
1 N lifts an apple
500 N is exerted when you sit on someone
33 000 000 N launches a rocket
17
ASSIGNMENT 1: FORCES AROUND YOU
Obtain a copy of this assignment sheet from your teacher.
1. Copy and complete the sentences below.
Choose from these words:
DIRECTION
(a)
(b)
(c)
(d)
(e)
PULL
MOVE
3.
Some forces can act over a distance,
rather than by contact.
(a) What does this statement mean?
(b) Name three types of forces which
can do this.
4.
What forces cause a bike to slow down
when you stop pedalling?
5.
You are sitting on a chair.
(a) There are two balanced forces.
What are they?
(b) What would happen if these forces
were not balanced?
6.
Imagine you are abseiling down a cliff.
What are the two forces acting on you?
Are they balanced?
7.
Forces are measured in newtons. How
would you explain to your parents how
big a force of 20 newtons is?
8.
A car travelling in a straight line at
constant speed has no forces acting on
it. Explain why this statement is false.
9.
A golfer hits a ball into the air. Is there
a force on the ball while it is in the air?
Explain.
10.
In which direction will this boat move?
Explain your answer.
PUSH
A force is a ____ or a ______
When you open a door, you _____
When you lift something, you ____
A force can make things _______
A force can also make moving things
change ________
2. The diagrams below show some forces in
action. The forces are shown with arrows.
(a) For each picture name the object that
the force acts on. For example,
in A the force acts on the ball.
(b) Choose from the list below to say what
the force is doing in each picture.
Is it
 starting an object moving?
 slowing down an object that is
moving?
 changing the direction of
movement?
 balancing another force and
preventing movement?
 bending an object?
18
ACTIVITY 7: FRICTION, A CONTACT FORCE
Friction occurs when any two surfaces in contact with each other try to move over each
other. Rub your hands together then repeat with a little soap and water on your hands.
Your hands slide over each other more easily. Why?
Friction always opposes motion.
Suppose you try to slide a heavy desk along the floor and it does not move. This is due to
the friction between the desk and the floor. This static friction (as it is named) is equal to
your push, but in the opposite direction. If you push a little harder and the desk still does
not move, then your push has been matched by an increase in the static frictional force. As
you push harder, the static friction increases until it reaches its maximum value, called the
limiting or starting friction. If you can push with a force greater than the limiting
friction, the desk will begin to slide.
Once the desk is moving, its motion will still be resisted by either:
sliding friction – the force opposing the movement of one body sliding over another or
rolling friction – the force opposing the movement of one body rolling over another.
The motion of objects travelling through fluids like air and water is opposed by fluid
friction. Air resistance is a form of fluid friction.
Friction occurs because surfaces are never completely smooth. The roughness of the two
surfaces means there are many points which catch and stick together.
Surfaces appear
to be smooth
Magnified view
of surfaces
Copy and complete the following table in your book
EFFECT OF FRICTION
GIVE AN EXAMPLE WHERE
THE EFFECT IS AN
ADVANTAGE
GIVE AN EXAMPLE WHERE
THE EFFECT IS A
DISADVANTAGE
Slows down movement
COPY AND COMPLETE
Causes wear
Produces heat
19
ACTIVITY 8: DOES THE TYPE OF SURFACE AFFECT FRICTION?
Aim: To measure the force of sliding friction between different surfaces.
Materials:




spring balance 0 – 20 N
1 metre of string
heavy object (e.g. wood block)
several different surfaces
Procedure:
1.
2.
3.
4.
5.
Connect the spring balance to the block of wood on your bench top.
Measure the horizontal force needed to move the object at a constant and slow speed
along the bench top. This force is equal to the opposing friction force.
Repeat the measurement twice and then calculate the average frictional force for this
surface. Make sure you record all your results in a suitable table.
Predict the force needed to slide the block over two different surfaces.
Repeat steps 2 and 3 for two different surfaces e.g. concrete, bitumen, grass etc.
Questions and processing data:
1.
2.
3.
4.
5.
Why was it necessary to take three measurements each time, instead of just one?
Draw a bar graph of your data.
What can you say about the roughness of the surface and the sliding friction force?
What is the direction of the friction?
What variables did you keep the same during your trials?
OTHER FACTORS CAN ALTER THE AMOUNT OF FRICTION?
Using the equipment you used in Activity 7, plus the suggestions below, your teacher will
most probably divide you into groups to investigate one of the activities below. You will
need to plan the activity yourself and write up a brief report using the headings: AIM,
PROCEDURE, RESULTS and CONCLUSION.
ACTIVITY 8A: How can friction be reduced? You could put round pencils, marbles or
wooden dowels under the block. Or you could try putting talcum powder, water,
detergent solution or glycerol between the two surfaces.
ACTIVITY 8B: What happens to the frictional force if you increase the mass of the
block? You might like to try putting extra masses on top of the block.
ACTIVITY 8C: How does the area of contact between the two surfaces affect the
friction? There is a special friction block that has grooves cut on one face to reduce
the surface area.
PHEW!! How
can I reduce
the limiting
friction?
20
ACTIVITY 9: REDUCING FRICTION
The pictures below show you some things which will only work when the friction is very
small.
Sometimes we want to keep the frictional forces small to save wear on moving parts.
Sometimes we want to keep the frictional forces small to make our work easier.
Sometimes we want to keep the frictional forces small to move faster.
REMEMBER: We can reduce friction by:



Using rollers or ball bearings
Making the surfaces smoother
Using a lubricant (oil, grease)
COPY AND COMPLETE THE TABLE BELOW IN YOUR BOOKS
PICTURE
Door hinge
Roller skate
Bicycle hub
Old watch
Slide
Roller
Ice skate
Bearing
Toboggan
How do we keep the frictional
force small? e.g. lubricant
Why do we want to keep the
frictional force small?
e.g. save wear
COPY AND COMPLETE
21
ACTIVITY 10: INCREASING FRICTION
The pictures below show you some things which will only work when there is a large
frictional force.
Sometimes we want to make the frictional forces larger to give a better grip.
Sometimes we want to make the frictional forces larger to wear away a surface.
Sometimes we want to make the frictional forces larger to produce heat.
REMEMBER: We can increase friction by:



Making the surfaces rougher
Using a large force to hold the surfaces together
Removing lubricants like oil and grease.
COPY AND COMPLETE THE TABLE BELOW IN YOUR BOOKS
PICTURE
Watch winder
Car tyre
Drum car brakes
Metal file
Matches
Knot in rope
Cigarette lighter
Bike pedal
Tennis racquet
Joggers
How do we keep the frictional
force large? e.g. rough surface
Why do we want to make the
frictional force large?
e.g. produce wear
COPY AND COMPLETE
22
ASSIGNMENT 2: FRICTION
Obtain a copy of this assignment sheet
from your teacher.
3.
CARPET
GLASS
1. Look at the diagrams below. Copy and
complete the sentences below, selecting the
correct words.
(a) Diagram A shows _______ (sliding/rolling)
friction.
(b) The friction in B is _____ (greater/less)
than in A.
(c) Rolling friction is ______ (greater/less)
than sliding friction.
(d) When an object slides there is _______
(more/less) resistance to movement than
when it rolls.
(e) With lubrication (Diagram C) you need
____ (more/less) force to move an object.
(f) Lubrication _______ (increases/decreases)
friction.
Copy and complete the paragraph below,
choosing from these words to fill the gaps:
FORCE
RUBS
ROUGH
SMOOTH
MORE
LESS
Things move more easily across a ______ surface
than a ______ surface. This is because of
friction. It happens when one surface ______ on
another. Rough surfaces like _____ produce
_____ friction than smooth surfaces like ______
4. Use your knowledge of friction to explain the
following:
(a)
Gymnasts rub rosin on their hands before
competing.
(b)
Cars that travel in snow have to carry
chains that fit around the tyres.
(c)
Surfers wax their surfboards.
(d)
A car uses more fuel when fitted with a
roof rack.
(e)
When you drive a car in city traffic for
some time the brakes become quite hot?
(f)
The front and underneath of the Space
Shuttle are covered with special heatresistant tiles.
A
5. Friction is involved in water skiing, abseiling,
running and writing. For each example:
(a)
B
(b)
(c)
C
2. What two factors influence the size of a
frictional force?
Name the two surfaces between which
friction acts,
Say what the force of friction is doing,
and
Say what would happen if the frictional
force suddenly disappeared.
6. For each of the following, describe how friction is
reduced:
(a)
Roller blades
(b)
A water slide
(c)
A jet flying at high speed
(d)
A door hinge
(e)
A bobsled
7. What is the purpose of the tread on a tyre? How
does it work on a wet road?
8. (a)
(b)
9.
Formula 1 racing cars use ‘slicks’ –
wide tyres with no tread. Discuss the
advantages and disadvantages of
these tyres.
How do the front and rear ‘spoilers’
improve the car’s performance?
Explain why frictional forces depend on the
surfaces in contact and the weight of the object.
23
ASSIGNMENT 3: FRICTION AND BICYCLES
HOW FORCES LIKE FRICTION AFFECT THE MOVEMENT OF BICYCLES.
Identifying friction forces.
1. On the sketch of the bicycle below label with arrows:
a)
b)
Note:
FIVE parts that need a LARGE Frictional force and
FOUR parts that need a SMALL frictional force.
Use different coloured arrows for large and small forces.
An example of how to complete your answer is shown below.
Understanding how friction is modified:
2. On the labelled sketch of the bicycle briefly describe how the friction is
made larger or smaller for each of the nine locations you have labelled.
OBTAIN A COPY OF THIS
ASSIGNMENT FROM YOUR
TEACHER
e.g. HANDLE GRIPS (Large
friction)
Friction Force made larger by using
……..
24
OPEN INVESTIGATIONS
Open Investigations are experiments, activities or investigations where you
have to solve a problem by designing your own experiment.
Rather than throw you in at the deep end we will do a sample open
investigation as a class so that when you get to the actual problem to
investigate you will have a framework which will help you.
There are FOUR parts to the Science Inquiry Skills Outcome.
Science Inquiry Skills include:
1. Questioning & Predicting
We observe things happening around us then attempt to answer the
question "Why is it so?"
We make hypotheses to account for our observations, then predict what
will happen if our hypothesis is tested.
2. Planning & Conducting
This involves working out how you are going to investigate your hypothesis;
what variables you will need to control or alter; what equipment you will
require etc.
Conducting investigations involves maybe a few preliminary trials to fine
tune any measurements you might take, then conducting the actual
experiment and using repeat trials to reduce the impact of any errors and
increase the confidence you might have in the results you obtain.
3. Processing & Analysing Data
Processing data involves the use of tables, graphs, summary sheets, etc.
to make sense of any measurements you took and present the information
you have gained in as simple a way as possible. From our data we draw
conclusions - what was found out?
4. Communicating
We let others know of our findings, sharing our ideas and findings.
The next few pages give:
1. A suggested topic for a sample investigation. Your teacher may choose
another.
2. Some important terms that will help you understand investigations.
3. A three page INVESTIGATION GUIDE that if followed closely will lead you
through the four steps of Science Inquiry Skills.
25
A SAMPLE OPEN INVESTIGATION
If your teacher wishes to introduce you to open investigations at
this stage of your Science course he/she could get you to do it in
class in groups or to do it for homework as an assignment.
THE PROBLEM TO INVESTIGATE:
We have just done some activities that show that friction is a force opposing
the motion of one body moving over another body.
Plan and conduct an investigation that would assist you in finding out
which shoe has the most grip or frictional drag?
PROCEDURE:
Work through the INVESTIGATION GUIDE as a class or small groups as
directed by your teacher. A good scientist spends most of the time planning
their investigation and only a short time actually doing or conducting the
experiment and collecting data. They then spend some time analysing the
data before drawing a conclusion. So do not be in a big hurry to start straight
away. The INVESTIGATION GUIDE will assist you in all four aspects of
investigating scientifically.
26
KEY TERMS USED IN SCIENCE INVESTIGATIONS
HYPOTHESIS:
A possible idea to be tested in an investigation stated as the relationship
between the independent and dependent variables. e.g. The more fertiliser you
put on wheat the faster it grows.
VARIABLE:
A factor that can be changed, kept the same or measured in an investigation.
INDEPENDENT VARIABLE:
The variable that is changed in an investigation to see what effect it has on the
dependent variable. e.g. the amount of fertiliser on plants.
DEPENDENT VARIABLE:
The variable that changes in response to changes in the independent variable.
Often it is the variable that is measured in an experiment. e.g. the growth of
the plants after different amounts of fertiliser have been added.
CONTROLLED VARIABLE:
A variable that is kept the same throughout the investigation. This is so you
can be sure that it is the change in the independent variable (amount of
fertiliser) that is causing the change in the dependent variable (growth of the
plants). An example of controlled variables would be the amount of water
added to each pot, the type of soil, the amount of soil etc.
PRELIMINARY TRIALS:
These represent a trial run of the procedure used to fine tune the method and
measurement techniques before doing the actual experiment and collecting
the data.
REPEAT TRIALS:
These are conducted to collect more data and to eliminate any errors that
might have been present if only one trial was used. For example, if you were
investigating the brakes on a bike you would do many trials and average the
results.
Lucky we did
a preliminary
trial!!
27
MOUSETRAP RACERS
RULES:
1. Design a three or 4 wheeled car that is propelled only by a standard
mousetrap, not a rat trap.
2. You can use other devices such as pulleys, gear wheels etc to assist.
3. The wheels can be as small or as large as you wish.
4. No more than three people in the design team
CERTIFICATES WILL BE AWARDED IN VARIOUS SECTIONS SUCH AS:
 LONGEST DISTANCE TRAVELLED.
 FASTEST
 MOST CRAZY AND WEIRD DESIGN THAT WORKS.
28
ACTIVITY 11: GRAVITY – A NON-CONTACT FORCE
When you throw a ball in the air – it comes down.
You can jump up in the air – but you cannot stay there.
You are being pulled down by the non-contact force of GRAVITY.
When you drop a pen, or something falls, it is because gravity pulls the object
towards the Earth. This gravitational force gives objects their weight.
Gravity is the pull of the enormous mass of the Earth on our bodies and any
other objects near the Earth’s surface. It is a non-contact or distance force,
since it is able to act over a distance, without the objects touching each other.
Sir Isaac Newton discovered that there is a small gravitational force that pulls
any two objects together. The size of this force depends on:


The masses of the objects, and
How far apart they are.
This force of attraction between any two objects is very small, but when one of
the objects is the Earth, the force is quite large.
There is a gravitational pull between the Earth and the Moon. This keeps the
Moon in place and causes tides on Earth. In a similar way, the pull of gravity
keeps satellites in orbit around the Earth. All objects on the Earth, including
ourselves, are attracted to the centre of the Earth so we do not fall off.
TRY THESE QUESTIONS:
1.
True or False.
(a)
Mass and weight are the same.
(b)
Mass depends on gravity.
(c)
Weight depends on gravity.
(d)
An astronaut has the same mass on Earth as on the Moon.
(e)
An astronaut has the same weight on Earth as on the Moon.
(f)
The Moon’s gravity is stronger than the Earth’s gravity.
(g)
Gravity only affects heavy things like iron and not light things
like feathers.
2.
3.
Suggest a reason why the Moon has no atmosphere.
(a)
Why is gravity slightly greater at the poles than at the equator.
(b)
Why is gravity slightly less on the top of Mt Everest than near the
Dead Sea.
4.
WHO AM I?
Born in 1642. Father died the day before I was born. Not very good at school.
Made fun of by the ‘brain’ of the class. Worked hard until I was the best in the
class. At about 18 my uncle talked my mother into sending me to Cambridge
University because I was a hopeless farmer. At 27 I became Professor of
Mathematics and made many famous discoveries. I was the first scientist to be
buried in Westminster Abbey.
29
HOW THINGS WORK
SIMPLE MACHINES
Machines help you do things more easily. The most common simple machines are:
LEVERS, WHEEL AND AXLE, INCLINED PLANES (RAMPS); PULLEYS and GEARS.
Complex machines such as cars, cranes, clocks and bicycles are built up of many simple
machines plus some electrical and hydraulic devices.
Machines help us do things more easily in three different ways:
1.
MACHINES MAGNIFY THE FORCE YOU USE.
If you have to move a really heavy rock, it is easier to use a crowbar (a lever) than to try to lift
the rock with your hands. The longer the lever, the smaller the force you need to exert to
move the rock. Machines that magnify the force you use are said to give a FORCE
ADVANTAGE.
2.
MACHINES CHANGE THE DIRECTION OF THE FORCE.
If you have to raise the sails on a yacht, the pulley at the top of the mast allows you to
change the direction of the force. You pull the rope down and the sail goes up.
30
3.
MACHINES MAKE THINGS GO FASTER.
If you push on the pedals of a bike, the back wheel turns much faster than the pedals.
Machines that make things go faster are said to give a SPEED ADVANTAGE or DISTANCE
ADVANTAGE.
Some machines give you a larger force
than you apply. Other machines make
things go faster. But no machine can
give you a bigger force AND go faster at
the same time. If this happened it would
mean that you were getting more energy
out of the machine than you put in and
this is impossible.
Machines transfer energy from the effort
to the load. Because of friction, machines
lose some energy as heat and sound.
LEVERS
A crowbar is a type of simple machine called a LEVER. A lever is a long bar or rod which
moves around a fixed point called the pivot or fulcrum. In the sketch above the fulcrum or
pivot is a small rock. The large rock is called the LOAD, and the force you apply is called the
EFFORT.
In this case the lever has a force advantage.
31
Sometimes you want a lever to have a
distance advantage rather than a force
advantage. Suppose you want to pull a fish
out of water quickly. You can use a fishing
rod as a lever to do this. The fulcrum is
placed close to the effort. The effort is much
larger than the load(fish), but the distance the
fish moves is much greater than the distance
your hands move when they apply the effort.
Pliers and scissors are made up of two levers
held together at the pivot (fulcrum) by a bolt
or rivet. They work just like the crowbar,
with the fulcrum between the load and the
effort but much closer to the load. This
means you only require a small effort to
apply a large force to the load.
Another type of lever is where you have the
pivot at one end of the lever and the effort is
at the other end. The load is between the
pivot and the effort. The wheelbarrow and a
nut cracker are common examples.
MECHANICAL ADVANTAGE:
You can get a measure of how useful a simple machine is by dividing the load by the effort.
This measure is called the mechanical advantage of the machine.
For example, if you exerted 100 N to lift a 600 N load in a wheelbarrow:
Mechanical advantage =
Load
------------Effort
=
600
------- = 6
100
32
ACTIVITY 12: LEVERS
AIM:
To investigate how levers make it easier to lift loads.
MATERIALS:




metre ruler
 retort stand
two sets of 50 g masses
 bosshead and clamp
pencil
 newton spring balance
two pieces of string to hang the mass holders from the ruler
PROCEDURE:
EFFORT
Part A:
1. Rest the metre ruler on top of the pencil
which is placed at the 50 cm mark.
2. Place a 500 g load 5 cm to one side of the
EFFORT ARM
pivot (fulcrum). This side of the system is
FULCRUM
called the Load Arm.
LOAD ARM
3. Place a 100 g mass on the other side of the
fulcrum.
4. Move the small mass out from the pivot until the load is just lifted. Measure the distance
from the fulcrum to the 100 g mass. This is known as the Effort Arm.
5. Replace the 100 g mass with a 200 g mass and repeat steps 3 and 4 and record the value
of the Effort Arm.
6. Find effort arm lengths when 300 g and 400 g masses are used.
LOAD
RESULTS: (Copy and complete this table in your notebook)
LOAD
Mass (g)
500
500
500
500
Force (N)
LENGTH OF
LOAD
ARM
(cm)
EFFORT
Mass (g)
100
200
300
400
Force (N)
LENGTH OF
EFFORT
ARM
(cm)
To change mass into a force – multiply the mass (in kilograms) by 10.
For example: 500 g = 500  1000 = 0.5 kg, therefore force = 0.5 x 10 = 5 newton
Part B:
1. Set up the ruler, stand and clamp, spring balance and masses to model a wheelbarrow.
Use the spring balance to measure your upwards effort to balance the load.
2. Experiment with this arrangement. Which position of the load makes the best
wheelbarrow.
Part C:
1. Set up the ruler, stand and clamp, spring balance and masses to model a fishing rod.
Use the spring balance to measure your upwards effort to balance the load.
2. Experiment with this arrangement.
33
QUESTIONS: [Answer these in your notebook]
1. Can you see any pattern in your results in Part A? (Hint: Look at the Load and Load
Arm and compare it with the Effort and Effort Arm.)
2. Calculate the mechanical advantage for the lever arrangements in Part A. Is it always
greater than 1? What is the mechanical advantage for your lever arrangement in Part B
and Part C?
3. Draw three simple sketches of the type of lever used in Parts A, B and C labelling the
effort, load and fulcrum (pivot).
INVESTIGATION:
How much water would be needed to balance a load of:



50 g
150 g
250 g
34
ACTIVITY 13: WHEEL AND AXLE
The steering wheel is an example of a simple machine called a wheel and axle. The axle is
the central rod or column and the steering wheel is attached to this axle.
Without the steering wheel you would
not be able to turn the axle. The
force required would be too great.
With a steering wheel, applying a
small force will turn the axle. The
bigger the steering wheel the easier it
is to turn. This is one of the reasons
why buses have a larger steering
wheel than cars. The wheel and
axle is a special case of a lever.
Where is the pivot?
Where is the effort?
Where is the load?
A doorknob, screwdriver and windlass are other examples of a wheel and axle.
Door knobs and screwdrivers are examples of
wheel and axles.
Find the wheel and axle in each of the
above examples.
What is work?
A scientist would say that work is done when a
force moves an object through a distance.
This can be written as
Work = Force x Distance
35
ACTIVITY 14: INCLINED PLANE
Aim: To investigate how an inclined plane allows you to do work more easily.
Materials: Wooden ramp, roller, spring balance.
Procedure:
Distance travelled
Constant
height
10o
angleslo
pe
Distance travelled
Constant
height
40o
1.
2.
slope
Use a spring balance to measure the force you need to pull the roller up the ramp at various
angles. Make sure the spring balance is dragged along at the same angle as the ramp. Do this
several times for each angle and record the average force.
To change the angle, push the ramp closer to the block so that the vertical height remains
constant. See diagrams above.
Results:
Angle of
ramp
Force (N)
1
2
3
Average
Distance
moved by
roller (m)
Work done =
force x distance
100
400
600
900
Questions:
1.
2.
3.
4.
What did you notice about the amount of work done in each case?
At which angle of the ramp was it easiest to do the work? i.e. the force required was the
lowest.
Was there any disadvantage in doing the work more easily?
This workman is finding it difficult to lift the drum onto the
back of his truck. Can you think of a way to do the same amount
of work an easier way? How should he get the drum onto the
back of the truck?
Inclined planes have a force advantage – you apply a small effort over a large distance to lift
or move a heavy load over a small distance.
Nails, axes, wedges, ramps, zig-zag roads up steep hills are all examples of inclined planes.
36
A jack is an example of a
screw. You use a small force to
lift the heavy load of the car. But
you have to turn the jack handle
many times to raise the car by a
small amount.
37
ACTIVITY 15: PULLEY SYSTEMS
Aim: To investigate the following pulley systems shown below.
500 g
Copy and complete the following table:
PULLEY SYSTEM
NUMBER OF PULLEYS
LOAD LIFTED (N)
EFFORT FORCE (N)
1
2
3
4
38
Questions:
1.
2.
3.
4.
Write a general comment about the way the effort required to lift a load changes as the
number of pulleys involved changes.
Calculate the mechanical advantage of the four systems.
Write a general comment about how the effort distance changes with the number of
pulleys used.
Predict the effort needed to lift the mass if you used eight pulleys.
A pulley is a grooved wheel with a rope or cable over it. A single pulley does not give you a
force advantage – it just changes the direction of the force. To magnify your force you need
to use more than one pulley. This allows you to lift very heavy loads by using only a small
effort. But you need a lot of rope to lift the object only a little way.
39
ACTIVITY 16: GEARS
Gear wheels are wheels with teeth on them. The teeth of one gear usually fit into the teeth of
another gear. Gears are used to transfer the force from one wheel to the other. In a bicycle,
the large gear wheel attached to the pedals is connected to the smaller gear wheel on the
back wheel by a chain.
The gear wheel attached to the pedals is called the driving gear and the back sprocket or
gear is called the driven gear.
Gears can speed things up or slow things down.
This arrangement of gears turns the
propeller faster than the motor
This arrangement of gears moves the
propeller more slowly than the motor
40
BICYCLE GEARS
Your teacher may wish to demonstrate this activity. Alternatively, you could do this
for homework.
COPY THE TABLE BELOW:
Highest
Gear
Lowest
Gear
Number of teeth on larger gear
Number of teeth on smaller gear
Number of teeth on larger gear
COPY INTO YOUR BOOK
Ratio =
Number of teeth on smaller gear
Number of turns of rear wheel
Number of turns of pedal
Ratio =
Number of turns of rear wheel
Number of turns of pedal
Procedure:
1. Place a bicycle upside down on the floor (or lift the back wheel of the bike off the floor by
sliding a piece of wood under the metal bracket which connects the seat and the back
forks. Support the wood on two desks or stools)
2. Put a chalk mark on the rear tyre.
3. Check that the bike is in the highest gear. The chain should be on the largest sprocket
on the front and the smallest sprocket on the rear wheel.
4. Count the number of teeth on the larger gear wheel i.e. on the pedal gear. Record the
result in your table. Count the number of teeth on the smaller gear (the rear sprocket)
and record the result.
5. Turn the pedal through five revolutions. Count the number of revolutions made by the
rear wheel. Record the result in the table.
6. Now change gears until the bike is in the lowest gear.
7. Repeat steps 3 to 5, recording your results in the table.
41
8. Calculate the ratios:
Number of teeth on larger gear
Number of teeth on smaller gear
and
Number of turns of rear wheel
Number of turns of pedal
for the highest and the lowest gear.
Questions:
1. In which gear, high or low, does five turns of the pedal produce the greater number of
turns of the rear wheel?
2. For a particular gear being used, is there a relationship between the above ratios as
calculated in your table? Explain your answer.
3. What happens to the value of the teeth ratio when a rider changes from high gear into
low gear?
4. What happens to the value of the turns ratio when a rider changes from high gear into
low gear?
5. Which rear sprocket would you use to ride up a steep hill?
6. Which combination of front and rear sprockets would you use for riding downhill?
GEAR RATIOS
Low gear and high gear in bikes (and other devices like cars and motor bikes that
use sprockets and gears) refers to the gear ratio that you have calculated in the
previous activity.
The gear ratio is found by dividing the number of teeth on the front driving
sprocket (near pedals) by the number of teeth on the rear driven sprocket.
If the front driving sprocket has 52 teeth and the smallest driven sprocket on the
rear wheel has 14 teeth, the ratio is about 3.7. When the largest driven rear
sprocket is used (28 teeth) then the ratio is about 1.9.
When the chain is attached to the smallest rear sprocket it is called a high gear
because it has the highest gear ratio of 3.7.
The lowest gear ratio on most 12 speed bikes is obtained by using the smaller front
sprocket (e.g. 40 teeth) and the largest rear sprocket (e.g. 28 teeth). This gives a
gear ratio of about 1.4.
TRY THESE:
1. A racing bike has a 14 teeth rear sprocket. If the gear ratio is 5, how many
teeth has the front chain wheel?
2. The two front sprockets on a bike have 42 and 56 teeth. The six back sprockets
have – 14, 15, 17, 20, 24 and 28 teeth. Which combination will give you gear
ratios of 2.8 and 3.0?
42