Learning activities and teachers’ notes
GCSE in engineering (double award)
Worksheet 1: Basic mechanisms
Teachers’ notes
Vocational relevance
The design and construction of engineering machines and components is underpinned by the use of a
range of basic mechanisms. All engineers need to apply their knowledge of basic mechanisms both to the
effective use of machinery and to the design of mechanical devices, jigs and fixtures. Wherever possible,
students should have access to examples of the use of basic mechanisms to underpin the work undertaken
within these task sheets. Mechanisms and control systems can be found in almost all aspects of life,
including many domestic appliances.
Tasks in this worksheet:
1.1
Cams
1.2
Cranks
1.3
Drives
1.4
Gears and gearing
1.5
Levers
1.6
Linkages
1.7
Machines that use screw threads
1.8
Pneumatics
1.9
Pulleys
1.10 Ratchets
1.11 Wheels, axles and gears
Guidance on teaching, learning and assessment

This is the student's introduction to basic mechanisms. It should begin with a teacher-led class
discussion about the importance of mechanical devices and safety issues in the workshop. It might
be useful to begin by looking at various mechanical devices and asking students to note down their
main characteristics. It would also be useful to ask them to consider and note health and safety
warnings in their engineering logbooks.

Visits to factories to explore the use of mechanisms would be useful wherever possible.

Wherever possible, students should be involved in using basic mechanisms within their own practical
work to reinforce learning.

It is essential that students know what is required to achieve different grades, GG to A*A*. Therefore
they should be given the assessment criteria from the appropriate awarding body.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task
The task sheets are self explanatory. Teachers/tutors may wish to use some or all of the sheets. While
some of the sheets are practical in nature, others can be undertaken outside the workshop as they relate
to research. All of the tasks provide the basic skills and knowledge required to satisfy the assessment
objectives, but it should be noted that students are required to apply their knowledge in a practical way to
the three units of the award. Moderators will be looking for the practical application of skills and
knowledge. Work produced for the tasks can be included in the portfolio work. However, it must relate to
the design and make tasks in hand.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.1
Cams
The aim of this task is to be able to answer the question ‘what is a cam and where are they used?’
Following a shape
Cams are used in many machines such as car engines, sewing and washing machines. They use the
movement of one part of the machine to control another part. The most common type of cam is a rotary
cam.
rotating shaft
radial surface
Overhead camshaft with pear-shaped cams
axis (or centre of rotation)
Time
You will need one hour of workshop time for this task sheet.
Safety
Be careful when looking at cams in machines to make sure the machine is isolated from the mains. Moving
parts can trap you.
What you need to do
1. Copy this table and its title:
Types of movement
Try to add one more example to each box. (Think of fairground rides)
A cam can be any shape .You need to make the cam move in the timing you want. This lever is called a
cam follower. The cam is usually turned by a rotating shaft and pushes a rod or lever up and down. The
lever may be made in such a way that its movement is made bigger (amplified) at its other end, such as to
open and close a valve in a car engine.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
The follower may have a small roller on the end of it so it can follow the shape (profile) of the cam more
smoothly. Often the follower is kept pressed against the cam by a small spring. Other types of cam are
linear cams and box cams.
2. Use thick card and drawing pins to make four cams of different shapes. You may be able to use a
modelling kit, such as Fischer Technik, to do this more easily.
3. Turn each cam once only and watch what happens to the follower. How many times does it rise and
fall? Record the movement on a graph like this:
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Learning activities and teachers’ notes
GCSE in engineering (double award)
3. You can easily calculate the movement that a cam will produce by subtracting the distance between
the centre of the cam and its shortest side from the distance between the centre and the longest side.
4. Copy and complete the following table:
5. Look at the cams below and work out what types of movement they create.
Useful links
www.technologystudent.com/cams/camdex.htm
www.flying-pig.co.uk/mechanisms/index.html
Extension task
Describe where cams are used and what they do in your own words. Use illustrations to help explain their
purpose.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.2
Cranks
All machines, however basic or complex, are made up of simple mechanisms. A mechanism is a device,
which changes an input motion and force into a desired output motion and force.
The crank is a mechanism used to convert rotary motion into either reciprocating or oscillating motion. The
simplest type of crank is a handle that is turned.
You will first need to understand these terms:

rotary

linear

reciprocating

oscillating
1. Read each definition given in the chart below.
Copy the chart into your engineering logbook and add your own example for each type of movement.
Add other examples of mechanisms that convert one type of motion into another.
2. Read this information carefully:
A crankshaft converts rotary to linear movement, or vice versa.
Crankshafts are used in internal combustion engines in cars, trucks and buses to convert linear motion into
rotary motion.
A common crank mechanism is one which converts rotary motion into reciprocating motion. The reciprocating
part of the mechanism slides backwards and forwards in a guide, or bearing. This mechanism is called a crank
and slider. This mechanism can be reversed to convert reciprocating motion into rotary motion.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
The crank can also be used to convert rotary motion into oscillating motion.

Look at the mechanisms below and name the input and output motion.

Give an example of how each mechanism could be used in a machine.

Find examples of other machines that use a crank mechanism and draw them in your engineering
logbook.
3. Cranks are used in a number of machine tools. Make a list of machines that use cranks.
Safety
Be careful when looking at cranks in machines to make sure the machine is isolated from the mains.
Extension task:
Describe where cranks are used and what they do in your own words. Use illustrations to help explain their
purpose.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.3
Drives
All machines, however basic or complex, are made up of simple mechanisms. A mechanism is a device,
which changes an input motion and force into a desired output motion and force.
Drive systems are used to connect a motor to a rotating output shaft.
The most common type of drive system in modern products is the gearbox. However, drive systems can
also be made from belts and pulleys.
A drive system can change



direction of rotation
velocity of rotation
amount of available torque or turning force
Drive systems are used in almost every product and system that contains a motor or engine, for example,
hi-fi systems, domestic appliances, cars and robots.
Time
You will need one hour of workshop time for this task.
Equipment and materials
Books, electronic resources
Pillar drill
Construction kits
Your engineering logbook to record your results
Safety
Always observe the rules for moving around the workshop safely.
What you need to do
1. Pulleys can be used to change the speed.
Make a model of a simple pulley system from simple materials or construction kits. Use and modify
your model to show:

a driven pulley rotating at the same speed as the drive pulley

a driven pulley rotating at a faster speed than the drive pulley

a driven pulley rotating at a slower speed than the drive pulley
Draw each solution in your engineering logbook.
2. Using your investigations in the first part of this task, calculate the speed and the velocity ratio of the
system using the formulae:
Driver speed x driver diameter = driven speed x driven diameter
3. Pulley systems are used to drive many sort of machines; the pillar drill is an example.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Make sure the power supply is switched off and carefully open the top cover on the pillar drill in your
workshop. The electric motor is connected to a set of stepped pulleys.
Draw the stepped pulley system in your engineering logbook.
When you are investigating mechanisms, make sure you never operate any machine with
the covers open or removed.
Investigate the pulley system used in

a washing machine

a vacuum cleaner

a bicycle
4. All transmission systems transmit rotation from one shaft to another by means of a flexible belt running
on pulleys or by a chain and sprocket. There is a wide range of belts available and you need to make
the most appropriate choice based on availability, ease of use, cost and so on.
Copy the grid below into your engineering logbook.
Give an example of how each is used and any advantages / disadvantages
[Please close up space before and after slashes in table above (Advantages/disadvantages).]
5. Shafts and couplings
A coupling is a joint that is used to connect rotating shafts together.
Look carefully at the six different shafts and couplings shown below. Identify each one and give a brief
description of its use.
1
2
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Learning activities and teachers’ notes
GCSE in engineering (double award)
3
5
6
4
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.4
Gears and gearing
Gears are toothed wheels that mesh with each other to transfer movement. As you already know, they
are so useful that they are all around us, in tin openers, cars, bicycles, hand whisks and so on.
These shafts will
point up. With other
gear types you can
slows down but gets
change this direction
more power
too.
Gears can do these things:

change the direction of movement

change the speed of movement (velocity ratio)

act as force multipliers allowing heavy loads to be lifted by smaller efforts (mechanical advantage)
An excellent way to start on this assignment is to view the TEP CD Rom on Mechanisms – ask your teacher
if it's available – which has animations of all of these movements.
Time
You will need two hours of workshop time for this task sheet.
Safety
Make sure any machine you study is fully isolated from the mains.
What you need to do
Changing direction
Work in a small group. You will need some Technical Lego or Fischer Technik, as gears are hard to make
without specialist equipment. In this short activity, you will experiment with different types of gear to see
how many ways you can turn the movement by 90 degrees.
1. Using a kit, connect together the following gear arrangements and test them out.
input shaft is horizontal
output shaft is now
vertical, so the direction
has changed
worm and worm wheel
bevel gears
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Learning activities and teachers’ notes
GCSE in engineering (double award)
2. For the following gear types, find a photograph or diagram and draw arrows to show which way the
gear turns.

Spur gear to spur gear

Spur gear/idler/spur gear

Bevel gear to bevel gear

Worm gear to spur gear
Then, for each one, answer these questions:

If you turn the gear once only, how many times does the other gear turn?

Does the output shaft lie in the same directions as the input shaft or has it turned the movement
round a 'corner' (through 90 degrees)?
Changing speed
The last exercise showed you how gears can be used to change the direction of rotation. Now we will look
at the ways that gears change the speed of a machine.
In this simple diagram, you can see that if the small gear was to turn say, 10 revolutions per minute, then
the large gear would turn much more slowly, maybe 40, the actual speed is easy to calculate. It is a ratio.
No matter how big the gear is, if it has three times as many teeth as the small gear, then the small gear
will be running three times as slowly.
bevel gears
10 teeth
40 teeth
The large gear turns once, the little gear will
have to turn four times. This is called a
velocity ratio of 4:1.
These bevel gears not only change the direction of turning, but
because they are different sizes, will also change the speed.
If you turn the handle about six times, then the drill will only
turn once. A ratio of 6:1.
3. Make a 'magic box’, which has three outputs turning at different speeds when only one handle is
turned.
Build a wall with three different gears. Turn a single handle on the other side of the wall and make the three
gear wheels on this side. Make them turn at different speeds if you have enough kit.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
4. Which is the better choice on an engine: gears or pulleys? You may have studied pulleys. When you
are designing machines you have to choose between gears and pulleys.
Gears can often be used instead of pulleys, but here are some differences:

Gears are noisy, pulleys are quieter.

Gears are always accurate in the number of turns they do, pulley belts can slip.

Gears need lubricating once in a while, pulleys do not.

Gears are expensive to repair, a pulley belt is cheap.
Useful links
http://science.howstuffworks.com/gear.htm
www.lego.com/education/machines/default.asp?pagename=page1_3_2&locale=2057
www.mos.org/sln/Leonardo/InventorsToolbox.html
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.5
Levers
Levers are used in the simplest machines. Wheelbarrows, scissors, pliers, barbeque tongs, screwdrivers
and nut crackers. These are just a few examples of simple machines that use a lever mechanism. Levers
are also parts of more complicated machines, for example, the brakes on a bicycle.
Time
You will need about two hours of workshop time.
Equipment and materials
•
Metre ruler with holes drilled at 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 95cm. The holes must be
large enough for the rod of a clamp to fit through and the ruler to move freely about it.
•
Mass pans or mass hangers
•
Newton meter (10N)
Read the procedure and list for any other equipment needed. Check the list with your teacher.
Safety
Wear protective clothing and eye protection.
Be careful when using heavy masses.
A risk assessment must be carried out before starting work.
What you need to do
You will be given two lever systems to investigate. One is a model of a wheelbarrow and the other a
model of a pair of scissors. Work with a partner and agree who will investigate which model. You must
determine the velocity ratio of each model. Then you must determine their mechanical advantage and
efficiency when different loads are being moved. Compare your results with those of your partner.
Modelling a wheelbarrow
1. Set up the metre ruler as shown in the diagram:
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Learning activities and teachers’ notes
GCSE in engineering (double award)
The metal rod is pushed through the hole at 5 cm and this is the axle of the 'wheelbarrow'. The mass
hung at various distance along the ruler is the load carried by the wheelbarrow, and the Newton metre
represents the person lifting it. Make sure the ruler moves freely about the rod.
2. Calculate the velocity ratio for each load position you are going to investigate using:
3. Add a 100g mass to the load pan or hanger at point A.
4. Use the Newton metre, attached to the ruler through the 95cm hole, to measure the force needed to
lift the load
5. Repeat for masses of 200, 300, 400, 500g.
6. Calculate the mechanical advantage using:
You can assume that 100g = 1N.
7. Calculate the efficiency using:
8. Repeat steps 3–7 with the load pan or hanger at points B, C and D. Copy the table below for each
velocity ratio (different positions of load and effort) you used:
[Please close up spaces on either side of slashes in table above (Load/N, Effort/N).]
Modelling a pair of scissors
1. Set up the metre ruler as shown in the diagram:
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Learning activities and teachers’ notes
GCSE in engineering (double award)
The metal rod is pushed through the hole at 30cm and this is the pivot point of the 'scissors'. The
mass hung at one end of the ruler (point A) is the load being 'cut', and the mass hung at the other end
is the load (the force with which something is resisting being cut).
2. Calculate the velocity ratio for each effort position you are going to investigate (points B, C and D)
using:
3. Add a 100g mass to the load pan or hanger at point A.
4. Add masses to the effort pan or hanger at point B until the load is balanced (the metre rule is
horizontal). Record the value of this mass.
5. Repeat for masses of 200, 300, 400 and 500g added to the load pan or hanger.
6. Calculate the mechanical advantage using:
You can assume that 100g = 1N.
7. Calculate the efficiency using:
8. Repeat steps 3–7 with the load pan or hanger at points B, C and D. Copy the table below for each
velocity ratio (different positions of load and effort) you used:
[Please close up spaces on either side of slashes in table above (Load/N, Effort/N).]
9. Looking at the results you obtained, and those of your partner, answers these questions.

For the model wheelbarrow, explain why
You may find the following diagram helpful:
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Learning activities and teachers’ notes
GCSE in engineering (double award)
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Learning activities and teachers’ notes
•
GCSE in engineering (double award)
For both models
- plot a graph of mechanical advantage (y-axis) against load/N (x-axis).
- plot a graph of efficiency/% (y-axis) against load/N (x-axis).
10. Explain why the velocity ratio equals the mechanical advantage for a 'perfect' machine.
11. Why isn't either of your machines 'perfect', in other words do not have a 100 per cent efficiency?
12. Your model wheelbarrow is doing both 'useful' work, by lifting the load you added, and 'useless' work,
by lifting parts of the wheelbarrow itself. It also has to overcome friction. Explain the shape of the
graph you drew for the model wheelbarrow.
13. How could friction be reduced in a wheelbarrow?
14. Ask one of the other students to cut (a) paper and (b) a thick piece of card with a pair of scissors.
What do you notice about where the paper or card is put in the scissors? Use your experimental
results to explain.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.6
Linkages
All machines, however basic or complex, are made up of simple mechanisms. A mechanism is a device
which changes an input motion and force into a desired output motion and force. This task sheet is about
linkages and levers.
A simple lever is a rigid bar which pivots at a fixed point called the fulcrum. A lever changes an input
motion and force into a desired output motion and force. Levers can be connected together to form
linkages.
Time
You will need one hour of workshop time for this task.
Equipment and materials
Books, electronic resources
Card, paper fasteners
Construction kits
Your engineering logbook to record your results
Safety
Always observe the rules for moving around the workshop safely. This equipment can trap you or your
Clothes.
What you need to do
1. The diagrams below show the three classes of lever.
Many kinds of tools contain lever systems. Look at the three common tools shown below:
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Learning activities and teachers’ notes
GCSE in engineering (double award)

Working in teams, decide which class of lever each item uses. Draw a chart to record your decisions.

Find three more tools which use lever systems, identify which class of lever they use and add them
to your chart.
2. Levers can be used to lift loads, create movement, or both.
Look carefully at the lever below.
To find out the effort needed to lift the load the moments in the lever system were calculated:

Copy the calculation and the diagram into your engineering logbook.

Calculate the mechanical advantage of the lever system shown above.
Find out how to calculate:

the movement created by a lever

the velocity ratio of a lever system
3. Bell cranks and reverse motion linkages can be used to change the direction of a motion.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
The brakes on your bike use the bell crank principle, helping you to stop safely.
Working in teams, look carefully at the bell crank brake system on the previous page.
In your engineering logbooks, describe

the input motion and force

the mechanism

the output motion and force
4. Linkages can also be used to make objects move in a line and keep them a set distance apart. This is
known as parallel motion. Parallel linkages can be used to copy or repeat movement, such as the lift
safety gates shown in the drawing below.
Working in teams use thick card and paper fasteners to construct a linkage system that could be used
as a framework for a folding chair. This should be able to support the user in two positions, as well as
packing flat for storage and transport. Record your solution in your engineering logbook.
You may use construction kits to do this more easily.
5. The diagram below shows how a toggle clamp system works.
Find an example of a tool in the workshop that uses this system.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.7
Machines that use screw threads
Many machines use a screw thread. Examples are G-clamps and vices (machines that can grip things very
tightly) and car jacks, very useful machines for moving high loads with little effort. These machines have
higher mechanical advantages than levers and pulleys.
Time
You will need about half an hour of workshop time.
Equipment and materials
Car jack
Safety
Wear protective clothing and eye protection.
A risk assessment must be carried out before starting work.
What you need to do
You will be given a car jack. Your task is to measure its velocity ratio. Then you should estimate the effort
needed for the jack to lift very large masses.
1. Examine the car jack and describe it in a few sentences. Use suitably labelled diagrams to illustrate
how the jack works.
2. If possible, use the jack to lift a very large mass – ideally a car! You will need to check with your
teacher to find out what you can do. Make a note of what you observe when using the jack.
3. Measure the pitch of the screw thread and the length of the Tommy bar used to turn it (you need to
decide how to make these measurements).
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Learning activities and teachers’ notes
GCSE in engineering (double award)
4. When the screw is turned one revolution it moves the distance of the pitch. To turn the screw one
revolution, the Tommy bar must also rotate once. The distance the outside end of the Tommy bar
turns is its circumference. Calculate the velocity ratio for the jack using:
5. Calculate the effort needed to move a 5000N load using a 2m lever that is pivoted 10cm from its
end, with the load at the end nearest the pivot and the effort applied at the other end. Now compare
this with the car jack you examined.
6. If the jack were 100 per cent efficient, the mechanical advantage would be the same as the velocity
ratio.
Write down the value you calculated for the velocity ratio of the jack.
7. Write an expression for mechanical advantage in terms of the effort and load.
8. Calculate the effort needed to move a 5000N load if the jack were 100 per cent efficient.
9. Explain why the jack is not 100 per cent efficient.
10. If the jack had an efficiency of 80 per cent, what effort is needed to move 5000N?
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.8
Pneumatics
Pneumatic machines are force multipliers. They are used in more complicated machines that move heavy
loads, such as JCBs, and in the braking systems in cars. Hydraulic presses also use pneumatics and are
used for compressing things like bales of hay, waste paper and scrap metal. Presses are also used to
shape metal body parts for cars and other fabricated articles. Pneumatics is an effective way of moving
high loads with small effort. These machines have higher mechanical advantages than levers and pulleys.
Time
You will need about one and a half hours of workshop time.
Equipment and materials

10cm3 plastic syringe

500cm3 plastic syringe

30cm plastic tubing

Araldite or similar glue

Masses (50–1000g)
Safety
A risk assessment must be carried out before starting work.
Wear protective clothing and eye protection.
Take care when using heavy weights.
What you need to do
You will use two different sizes of syringe to model a hydraulic press. You will measure its mechanical
advantage and efficiency.
1. Measure the diameters of the two syringe barrels and calculate their cross-section areas.
2. Join the two syringes by gluing the plastic tubing to the nozzles of the barrels. Take care not to block
the nozzles with glue. Once set up this arrangement should be kept for future use and not taken
apart.
3. Set up the apparatus as shown in the diagram on the next page:
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Make sure the barrel of each syringe moves freely. The barrels are the pistons of your hydraulic
machine.
4. Calculate the velocity ratio using:
5. Place a 200g mass on top of the ram piston. This is the load.
6. Add masses to the pump piston until the ram begins to move slowly and steadily. Record the mass
needed. This mass allows you to calculate the effort required.
7. Repeat for masses of 300, 400 and 500g on the ram piston. You will need to set up an arrangement
that makes sure the masses do not slip off the piston.
8. Calculate the mechanical advantage at each load using the formula
[Please close up space between ‘100’ and ‘g’ and between ‘1’ and ‘N’]
9. Calculate the efficiency at each load using the formula.
10. Remove all masses, take out the pistons and fill the syringes and tubing with water. Repeat steps 5–9.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
11. In your engineering logbook, complete the table:
[Please close up spaces before and after slashes in line 6 of table below]
12. Plot graphs of efficiency/% (y-axis) against load/N (x-axis) for each of the machines (air-filled and
water-filled).
13. Why are the pneumatic machines you made not 100 per cent efficient?
14. Your machine is doing both 'useful' work, by lifting the load you added and 'useless' work by lifting
parts of the machine itself, compressing the gas or liquid in the system and in overcoming friction.
Explain the shapes of the graph you obtained.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.9
Pulleys
Hoists are often used in the workplace to lift heavy loads. They use systems of pulleys as 'force multipliers',
allowing high loads to be lifted by small efforts. A common set-up used in the workplace for lifting
very heavy loads is the block and tackle.
Time
You will need about two hours of workshop time.
Equipment and materials

Pulley systems

Mass pans or mass hangers
Read the 'what you need to do' section and list any other equipment needed. Check the list with your
teacher.
Safety
A risk assessment must be carried out before starting work.
Wear protective clothing and eye protection.
Be careful when using heavy masses.
What you need to do
You should work in a team. The team will be given a number of pulley systems to investigate and you
must decide who will investigate each system. For the pulley system you study, you must determine its
velocity ratio. Then you must determine its mechanical advantage and efficiency when different loads are
being raised. At the end of the work you should compare the results you obtained for all the pulley systems
investigated by the team.
Determining velocity ratio (VR)
1. Set up the pulley system as shown in the diagram on the next page:
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Learning activities and teachers’ notes
GCSE in engineering (double award)
2. Add a 100g mass to the load pan or hanger and attach a needle (or other pointer) to the bottom of
the pan or hanger. Clamp a metre ruler alongside so the distance moved by the pan or hanger can be
measured.
3. Add a mass to the effort pan or hanger sufficient to pull the string taut. Attach a needle to the bottom
of the pan or hanger. Clamp a second metre ruler alongside so the distance moved by the effort can
be measured.
4. Now pull the effort pan of hanger so the load is raised 10, 20, 30, 40 and 50cm. For each distance,
measure how far the effort is moved.
5. Calculate the velocity ratio for the wheel and axle you are using:
6. Calculate the mean (average) value for the velocity ratio.
Determining mechanical advantage (MA) and efficiency
1. Remove the 100g mass and replace it with a 50g mass on the load pan or hanger.
2. Pull the effort pan or hanger until it is taut and then add masses until the load begins to rise slowly
and steadily.
3. Repeat for masses of 100, 150, 200, 250, 300, 350, 400, 450 and 500g on the load
pan or hanger.
4. Calculate the mechanical advantage at each load using the formula
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Learning activities and teachers’ notes
GCSE in engineering (double award)
You can assume that 100g = 1N.
5. Calculate the efficiency at each load using the formula
6. Complete the following table for the pulley system you were given to study:
[Please close up spaces before and after slashes in second line of table above]

Plot a graph of mechanical advantage (y-axis) against load / N (x-axis).

Plot a graph of efficiency/% (y-axis) against load/N (x-axis).

Explain why the velocity ratio equals the mechanical advantage for a 'perfect' machine.

Why isn't your machine 'perfect', in other words doesn't have a 100 per cent efficiency?

Where is there friction in your machine?

What would happen if your machine were 'friction-free'?

Your machine is doing both 'useful' work by lifting the load you added and 'useless' work by lifting
parts of the machine itself and in overcoming friction. Explain the shape of the graphs you have
drawn.

Compare your results with those of the rest of the team who investigated different pulley systems.
Write a paragraph that summarises the comparison. What trends or patterns did you notice?
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.10
Ratchets
All machines, however basic or complex, are made up of simple mechanisms. A mechanism is a device
which changes an input motion and force into a desired output motion and force.
This task sheet deals with ratchet mechanisms.
A ratchet mechanism is based on a wheel that has teeth cut out of it and a pawl that follows as the wheel
turns:
Time
You will need one hour of workshop time for this task.
Equipment and materials
Books, electronic resources
Construction kits
Your engineering logbook to record your results
Safety
Always observe the rules for moving around the workshop safely.
What you need to do
1. Working in teams, model a ratchet and pawl mechanism.
Look carefully at the mechanism. Draw the ratchet and pawl mechanism in your engineering logbook.
Label your diagram.
•
Add notes to explain in detail what happens to the pawl when you rotate the ratchet in a
anticlockwise direction.
•
Explain what happens if you try to turn the ratchet in the opposite direction. You may find these
key words useful: grooves, radial, pawl, teeth, circumference.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
2. Two examples of ratchet mechanisms are shown below.
Winding drum
Wrench
Copy the grid below into your engineering logbook. Investigate these everyday items that use ratchet
mechanisms: Draw the object and explain the function of the ratchet mechanism in each case.
Add two further examples of your own.
Useful links
www.flying-pig.co.uk/mechanisms/pages/ratchet.html
www.automata.co.uk/ratchets.htm
3. Working in teams, design a ratchet mechanism to fit in the back of a delivery van. This system will be
used to lift heavy packages from the van to ground level. Use drawings and notes to explain your
design. Record your ideas in your engineering logbook.
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Learning activities and teachers’ notes
GCSE in engineering (double award)
Task 1.11
Wheels, axles and gears
Gears are used in many machines, for example, bicycles and cars. Wheels and axles are also used and
an investigation of them will help you understand how gears work.
Time
You will need about two hours of workshop time.
Equipment and materials

Wheel and axle systems, with wheels and axles of different diameters

Mass pans or mass hangers
Read the 'what you need to do' section and list any other equipment needed. Check the list with your
teacher.
Safety
A risk assessment must be carried out before starting work.
Wear protective clothing and eye protection.
Be careful when using heavy masses.
What you need to do
You should work in a team. The team will be given some wheel and axle systems to investigate. It must
decide who will investigate which system. You must determine the velocity ratio of the one you are given.
Then you must determine its mechanical advantage and efficiency when different loads are being raised.
1. Measure the diameters of the wheel and axle.
2. Calculate the velocity ratio for the wheel and axle you are using:
3. Set up the wheel and axle as shown in the diagram on the next page:
32
Learning activities and teachers’ notes
GCSE in engineering (double award)
4. Add a 100g mass to the load pan or hanger attached to the axle.
5. Pull the effort pan or hanger (attached to the wheel) until it is taut and then add masses until the load
begins to rise slowly and steadily.
6. Repeat for masses of 200, 300, 400, 500, 600, 700 and 800g on the load pan or hanger.
7. Calculate the mechanical advantage at each load using the formula
You can assume that 100g = 1N.
8. Calculate the efficiency at each load using the formula
9. Complete the following table and record it in your engineering logbook:
[Please close up spaces between slashes in first line of table above (Load/N, Effort/N)]
10. Plot a graph of mechanical advantage (y-axis) against load/N (x-axis).
11. Plot a graph of efficiency/% (y-axis) against load/N (x-axis).
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Design Assignment 8: Theme Park Ride
GCSE in Engineering (Double Award)
12. Explain why the velocity ratio equals the mechanical advantage for a 'perfect' machine.
13. Why isn't your machine 'perfect', in other words, is not 100 per cent efficient?
14. Where is there friction in your machine?
15. What would happen if your machine were 'friction-free'?
16. Explain why the velocity ratio of two gears = number of teeth in the driven gear
number of teeth in the driver gear
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