Pulley Force Lesson Plan
Amount of time Demo takes:​ 5 mins.
Try this at home!
Materials
Table Top
● Pulley base and stand
● Pulleys (10)
● Green chord
● Anchor
● Red base pulley
● Ring stand hooks (8)
● Mass hooks (8)
● Masses
● Requires 5’ of table space
Hands On
● Gloves (3 pair)
● Rope
● Poles (3)
Set-up Instructions
Table Top
1. Remove the wooden base. Attach two metal rods to the base; sandwich
the base between the washers and fasten the nut tightly. Set the stand
upright and set the remaining metal rod on the uprights (note the two
holes that fit neatly over the pegs on the upright rods.)
Hands On
1. Take out both poles and secure one end of the rope to the center of
one of the poles.
2. Loop the rope around the other pole so that the end of the rope can be
held by someone holding the pole that the rope is secured too.
SAFETY!
● Be careful of metal and wood splinters and sharp edges.
● Don’t drop a weight on your foot!
● Be sure anyone handling the rope or poles is wearing a pair of gloves
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● When holding the pole it must be held with two hands with the rope
between them
● All people involved must be facing each other
● Do not let anyone over force themselves, they can apply moderate force
but nothing excessive
● Remind people to not let go during the challenge, if this happen people
may end up getting injured
Lesson’s Big Idea
● Pulleys change direction of applied force and reduce the amount of work.
● Pulleys can make heavy objects easier to lift.
Background Information
● A pulley, one of the six simple machines, is a wheel on an axle that allows
movement of a cable/belt along its’ circumference. They’re used to lift
loads, apply forces, and transmit power. Mechanical advantage is formed.
● A rope/pulley system is the use of a single continuous rope to transmit a
tension force around one or more pulleys to lift/move a load.
● A block and tackle is assembled so one block is attached to fixed mounting
point and the other is attached to the moving load. The mechanical
advantage is equal to the number of parts of the rope that support the
block.
● Mechanical advantage is the number of parts of the rope that a
​ ct​ on the
load.
● ​ If there are ​p parts of the rope supporting the load W
​ . A balanced force on
the moving block
​
has tension in each of the parts of the rope as W
​ /p. Block
and tackle reduces the input force by the factor p
​ .
● A gun tackle has a single pulley in both the fixed and moving blocks with
two rope parts supporting the load W
​ .
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● Separation of the pulleys in the gun tackle show the force balance that
results in a rope tension of W
​ /2.
● A double tackle has two pulleys in both the fixed and moving blocks with
four rope parts supporting the load W
​ . The formula for below W/4.
● How it works:
○ Pulley systems assume the pulleys and lines are weightless, and no
energy is loss due to friction. Assumed is the lines don’t stretch.
○ In equilibrium, the forces on the moving block must sum to zero. In
addition the tension in the rope must be the same for each of its
parts.
● The load ​F on the moving pulley is balanced by the tension in two parts of
the rope supporting the pulley.
● Different types of pulley systems:
○ Fixed: An axle mounted in bearings attached to a supporting
structure. Changes the direction of the force on a rope or belt that
moves along its’ circumference. Mechanical advantage is gained by
combining a fixed pulley with a movable pulley or another fixed
pulley of a different diameter.
○ Movable: An axle in a movable block. A single movable pulley is
supported by two parts of the same rope.
○ Compound: Combination of fixed and movable pulleys; forms a
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block and tackle​.
Fixed
Movable
Compound
Instructional Procedure
Table Top
1. Set up a pulley system. Below is a fixed pulley demo that shows the
mechanical requirement of lifting 100GM. This setup has both fixed and
moving pulleys to show work required to move the mass is much less.
Both are anchored to the black anchor. All the participant has to do is
pull the lines to feel the difference.
2. Encourage participants to create pulley systems of their own if wanted.
Hands On
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1. Allow participants to decide who is going to be in what role
a. Base - The person holding the pole the rope is tied off to
b. Load - The person holding the Pole the rope is looped around
c. Worker - The person that will be holding the end of the roap
2. Have the Base and Load participants to stand about 5 ft to 8 ft apart
and have the Worker with the end of the rope next to the Base.
3. Have the Worker try to pull the Base and load together with one loop
around the poles, do not use excessive force.
4. After they try with one loop add another and then have the participants
try again. It should be easier for the Worker to pull the Base and load
together.
5. Repeat step four 2 or 3 more times to demonstrate the more loops you
add the easier it is for the Worker to pull together the Base and load.
6. You can use the table top demo to explain the science behind it.
Assessment/sample questions you can ask
1. Why does it take less force to lift the same amount when using a pulley
system?
2. What is a block and tackle?
3. Can you get mechanical advantage with a fixed pulley or a moving pulley?
4. Why does it get easier to pull the Base and Load together?
Clean Up
● Discard any pieces of trash or string.
● Make sure all objects are clean and dry and place them back in the bin.
Dis-assemble rod stands and fasten each nut to the rods with washers so
they will not get lost.
References
● http://en.wikipedia.org/wiki/Pulley
● http://youtu.be/z6XyLQC_RRQ
Next Generation Science Standards
● K-5
○ K-PS2-1
○ 4-PS3-4
● 6-8
○ MS-ETS1
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○
○
● 9-12
○
○
MS-PS2-2/4
MS-PS3-2
HS-PS2-1
HS-PS3
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