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LCPS Core Experience | Simple Machines Investigation ONE
Simple Machines
Stu de nt No tes
OBJECTIVES
Students will:
 identify how simple machines change the force needed to lift a load
 discover that simple machines make work seem easier by changing the
direction of a force
 changing the distance over which the force is exerted to lift a load
 calculate the mechanical advantage of pulley systems.
 learn how effort and load forces affect the mechanical advantage of pulleys
LINK
1. What are some everyday examples of pulleys?
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2. How do pulleys change the amount of work done to lift a load?
a. Work is less
b. Work is more
Materials Per Lab Group
 1 physics stand w/pulleys set
 1 pair of scissors
 1 meter stick
 1 metric ruler
c.Work is the same
 3 square masses (200g ea.)
 1 calculator
 1 spring scale
Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
Background
A pulley is one type of simple machine. It consists of a small wheel with a
groove that a rope or string can slide over. It is used to lift heavy objects, such
as the sails of a ship. Pulleys can be fixed to an immovable object or they can
be freely floating.
Simple machines work with forces. The input force is the force applied to the
machine. The input force is the same as the effort force. The output force is
the force the machine applies to the load lifted. The output force is sometimes
referred to as the load force. In a pulley system, the input force is applied to
the rope or string and the output force is applied to the load you are lifting.
The distance the rope (attached to the wood) moves toward the pulley is the
load distance. The length of rope or string from the pulley to where the effort
is applied is called the effort distance.
Pulley
Load
Distance
Effort
Distance
Output
Force
Load
Input
Force
EXPERIMENT
Lesson One: Mechanical Advantage of 1-Pulley and 2-Pulley Systems
1. In this Lesson, you will investigate the mechanical advantage of a 1-pulley
and a 2-pulley system.
2. Make a Prediction: How will using a pulley system affect the input force
required to lift a load?
Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
3. Record your data in Table A for one and two pulley
systems.
4.
Question: Which pulley system made it feel easier to lift
the load?
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Question: Which pulley system used the longest length of string to lift the
load?
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5.
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Background
When a load is lifted over a certain distance, the work done to lift the load can
be calculated. Work takes into account the properties of force and distance.
Work is calculated using the following formula:
Work = F × d
F = Force, measured in Newtons
d = distance, measured in meters
The units for work are joules. One joule = 1 Newton-meter.
13. Calculate the work done on the block. This work is equal to the output force
times the load distance. The work done on the load should be the same for
all configurations of the strings because the weight of the block and the height
it was lifted did not change. Record these work values in Table A.
Work done on the load = output force × load distance
Work done on the load in a 1-pulley system = ______________________
Work done on the load in a 2-pulley system = ______________________
Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
14. Next, calculate the work you did as you pulled on the string to lift the block. In
this case, multiply the input force times the effort distance. For each
different pulley system, record the work done by you in Table A.
Work done by you = input force × effort distance
Work done by you in a 1-pulley system = ____________________
Work done by you in a 2-pulley system = ____________________
15. Question: Look at the work done to lift the load (work output) and the work
done by you (work input) columns of your data table. What do you notice
about the amount of work output relative to the amount of work input?
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16. Question: Was more work done by the 2-pulley system or the 1-pulley
system?
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Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
Background
Although work may seem easier if a simple machine is used, machines do not
decrease the amount of work done. This concept can be expressed by the
term mechanical advantage. Mechanical advantage describes the
relationship between the input force (force needed to lift the load) and the
output force (force of gravity on the load). This can be expressed
mathematically by the following equation.
Mechanical Advantage 
Output Force (N)
Input Force (N)
For example, the mechanical advantage of the pulley might be shown as
Mechanical Advantage 
1.6 N
1.6 N
1
The amount of work done to lift a load may “seem easier” if a machine offers a
mechanical advantage greater than 1. A mechanical advantage greater than
1 occurs if the machine allows the user to exert less force to move the same
amount of load than if a machine were not used. In other words, the input
force will be less than the output force.
For example, in a machine that offers a mechanical advantage of 2, the input
force needed to lift a load will be half (½) the output force. This means that a
person using the machine would only exert half the force than if lifting the load
without the machine.
17. Calculate the mechanical advantage of the 1-pulley system and the 2-pulley system.
18. Place your answers in Table A.
Mechanical advantage of a 1-pulley system = Output Force =
Input Force
Mechanical advantage of a 2-pulley system = Output Force =
Input Force
19. Question: Compare the pulley systems. As the mechanical advantage
increased, what happened to the length of the string you have to pull to raise
the bottom block?
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Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
STOP AND DISCUSS
Table A before moving on to Lesson Two
Lesson Two: The Relationship Between Work and Mechanical Advantage
1. In Lesson Two, you will investigate the relationship between the amount of
work done and mechanical advantage. This trial uses only a 2-pulley system.
2. What is the mechanical advantage of a 2-pulley system? (You discovered this in
Lesson One.)_______________________
Make a Prediction: Do you think mechanical advantage will change as the
load becomes heavier? In other words, will the advantage of using a double
pulley system change as the mass of the load increases?
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3. Using the formula for work (W = F x d) calculate the work done on the load for
all three masses lifting the block 20 cm (0.20 m). Record in Table B.
Work done on the load = output force x load distance
Work done on the load (1 mass) = ______________________
Work done on the load (2 masses) = ______________________
Work done on the load (3 masses) = ______________________
4. Now find the mechanical advantage for each load. Record in Table B.
Mechanical Advantage 
Output Force
Input Force
5. Question: Did the amount of work change as you increased the loads?
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6. Using the formula for work (W = F x d) calculate the work done on the load for
all three masses lifting the block 40 cm (0.40 m). Record in the second half of
Table B.
Work Done on the Load = Output Force x Load Distance
Work done on the load (1 mass) = ______________________
Work done on the load (2 masses) = ______________________
Work done on the load (3 masses) = ______________________
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LCPS Core Experience | Simple Machines Investigation ONE
7. Now find the mechanical advantage for the second set of data. Record in the
second half of Table B.
Mechanical Advantage 
Output Force
Input Force
8. Question: Does the mechanical advantage of the 2-pulley system change as
the mass of the load increases?
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9. Question: Does the mechanical advantage of the 2-pulley system change as
the load distance increases? Why or why not?
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Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
LEARNING REVIEW
1. As the mass of the load increased, what happened to the load force, the effort
force and work? Explain.
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2. In Table B, a 2-pulley system was used. Was there a difference between the
input force and output force? Explain.
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3. Theoretically, the input force and output force are equal in a 1-pulley
system because it has a mechanical advantage of 1. Referring to your data
from Table A, what then is the benefit of using a 1-pulley system to lift a
load?
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4. Using your data from Table B, compare the load distance and the effort
distance in the 2-pulley system. Was there a difference in these distances?
Explain.
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STOP AND DISCUSS
Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
EVALUATION
1. How does the input force in the 2-pulley system compare to that in the 1pulley system?
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2. How does the effort distance compare in the different pulley systems?
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3. Compare the “work done on the load” in the 1-pulley and 2-pulley systems.
Why is the work similar if the input force is different for both systems? (Why
might the work “feel easier” with the 2-pulley system?)
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4. Think about the mechanical advantage of the 2-pulley system. Does the 2pulley system allow a person to apply less force to lift a load than the force of
gravity on the load? Use your data from Table B to support your answer.
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Simple Machines Investigation ONE
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LCPS Core Experience | Simple Machines Investigation ONE
Table A: Mechanical Advantage of 1-Pulley and 2-Pulley Systems
# of
Pulleys
Load
Distance
(m)
1
.20
2
.20
Extension
3
.20
Effort
Distance
(m)
Input Force
(N)
Output Force
(N)
Work Done
on Load
Work Done
by You
=Output Force x
Load Distance
=Input Force x Effort
Distance
(J)
(J)
Mechanical
Advantage
= Output Force
Input Force
Table B: The Relationship Between Work and Mechanical Advantage
Work
Work
Done
Done
Mechanical
on
Load
on
Load Mechanical
Load
Effort
Input Output
Load
Effort Input Output
Advantage
Mass
Advantage
=Output
=Output
Distance Distance Force
Force
Distance Distance Force Force
= Output
Load
Force x
Force x
=Output Force
Force/ Input
(m)
(m)
(N)
(N)
(m)
(m)
(N)
(N)
Load
Load
/ Input Force
Distance
Force
Distance
(J)
1 mass
(200 g)
.20
4.3
2 mass
(400 g)
.20
6.3
3 mass
(600 g)
.20
8.3
(J)
.40
.40
.40
Simple Machines Investigation ONE
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