n
o
s
3: Pulle
s
e
L
y
Pow
er
Have you ever raised or
lowered a window shade?
You likely used another type of
simple machine—the pulley. Pulleys make
lifting easier. You raise something by pulling down on a line,
instead of having to lift it up. Today you will examine how
pulleys work. You will also make your own pulley.
pulley: a
wheel-and-axle
system used
to change the
direction of an
applied force
Picture yourself on a
sailboat. The wind is
blowing, and it is time to
raise the sails. How are you
going to do it? Will you
climb the mast, holding on
to the end of the sail? Sails
are heavy. That would be
hard and dangerous work.
There is an easier way.
A pulley has a rope, belt,
or chain wrapped around
a wheel and axle. How does
a pulley work?
Try this simple activity:
Home In
str
uctor
Science 4
1. Throw a rope over a tree branch. (If you do not have access to
a tree, ask permission to use a door, shower rod, closet rod,
or other suitable item.)
2. Tie a heavy object to one end of the rope. You could use a
large book, a 2-kg bag of sugar, or something similar.
3. Pull on the other end of the rope.
30
Copyright ©2006, Alberta Education
Science 4: Module 1
The rope and tree branch work as a pulley. To lift the object, you
pull down on the rope. Without the branch, you would have to
lift the object up. Which would be harder? The machine—the
pulley—has changed the direction of the force you use to lift the
object.
A branch is not very
smooth. There is a lot
of friction between the
rope and the branch.
A wheel and axle can
help reduce friction,
making pulling easier.
To make things safer,
pulleys use a grooved
wheel. The groove
helps to keep the rope
in place.
Can you see how a pulley would help you raise the sails in a
sailboat? Lines work through several wheels and the top of the
sail attaches to the end of one line. As you pull on the other end
of the line, the sail rises.
simple pulley: a
pulley with one
wheel
fixed pulley: a
pulley attached
to something that
does not move
A simple pulley is a pulley with one wheel. A fixed pulley is a
pulley attached to something that does not move. It might
attach to a ceiling or the mast of a sailboat. A movable pulley is a
pulley attached to the thing you are lifting—the load.
movable pulley: a
pulley that moves
with the load
load: object or
material to be
moved
Fixed Pulley
Section 1: Lesson 3
Copyright ©2006, Alberta Education
Movable Pulley
31
Fixed pulleys and movable pulleys
both help you lift objects, but they
do so in different ways.
Explore fixed and movable pulleys
in the following activity.
A
ity 3: Lifting
v
i
t
c
the
Eas
yW
ay
What you need
• a metal coat hanger
• 2 chairs
• a broom or dowel
• an empty spool from thread
• scissors
• 2 m heavy string, cord, or twine
• a plastic bucket with a sturdy handle
• stones, marbles, or other heavy objects
• a ruler
• duct tape or masking tape
• a felt marker
• pliers
• gloves (optional)
Note: You could use a sewing machine bobbin instead of the
spool from thread.
32
Copyright ©2006, Alberta Education
Science 4: Module 1
What to do
Part A: Fixed Pulley System
Look at the diagram to help with this activity.
Have an adult help you unwind the wire around the neck of the metal
hanger. The ends of the wire may be sharp.
Home In
str
uctor
Science 4
1. Ask an adult to help you unwind the wire coiled around the
neck of the hanger. Use the pliers. Wear gloves to help protect
your hands.
2. Slip the spool over the end of the wire and position it in the
middle of the hanger. Then tape the neck of the hanger back
together.
3. Place the two chairs back to back and lay the broom across the
top of the backs.
4. Tie a loop of rope around the broomstick and hang the hanger
from it. (See the diagram at the beginning of this activity.)
Section 1: Lesson 3
You could also simply suspend the hanger from the
broomstick.
Copyright ©2006, Alberta Education
33
5. Cut a piece of string or cord about 1.5 m long and tie one
end to the handle of the bucket. Loop the other end over the
spool. Partly fill the bucket with stones, marbles, or other
objects. Don’t make it too heavy!
Home In
str
uctor
Science 4
Ask your home instructor to help you do the measurements.
6. This is a fixed pulley. Measure
30 cm from the pulley toward
the bucket. Mark this spot on
the rope. Use a felt marker. Pull
the rope downwards until the
mark on the rope comes up to
the pulley.
30 cm
7. Measure how far the bucket lifted off the ground.
Distance the bucket lifted off the ground:
cm
8. Now answer the following questions.
34
a. In which direction did you apply the force to the rope—up
or down?
b. As you applied the force, in which direction did the load
move?
c. When you pulled the rope, the load moved. Did the load
move less, the same, or more than the distance you pulled
the rope?
Copyright ©2006, Alberta Education
Science 4: Module 1
Part B: Movable Pulley System
Look at the diagram to help with this activity.
9. Remove the short rope that attached the hanger to the
broomstick.
10.Tie one end of the long rope to the broomstick. (See the
diagram.)
11.Hang the bucket from the hook on
the hanger and loop the rope under
the spool. This is a movable pulley.
30 cm
12.Hold the free end of the rope against
the broomstick. Pull on the rope
until the load just lifts from the
floor. Use the felt marker to mark the
rope at the top of the broomstick.
Measure 30 cm down the rope and
mark it there as well.
Now pull the rope up until the
second mark is at the top of the
broomstick.
Section 1: Lesson 3
Copyright ©2006, Alberta Education
35
13.Measure how far the bucket has moved.
Distance the bucket moved:
cm
14.Now answer the following questions.
a. In which direction did you apply the force to the rope—
up or down?
b. As you applied the force, in which direction did the load
move?
c. When you pulled the rope, the load moved. Did the load
move less, the same, or more than the distance you pulled
the rope?
Note: Save the pulley you created in this activity. You will use it
in Lesson 4.
Check your answers for this activity in the Suggested Answers at the
end of this lesson.
You found that a fixed pulley changes
the direction of the force needed to
move an object. You can lift something
by pulling down instead of lifting up.
This seems easier because your body’s
weight helps you pull down. The load
will move the same distance that you
pull on the rope.
36
Copyright ©2006, Alberta Education
Science 4: Module 1
With a movable pulley, both ends
of the rope support the load. The
fixed end of the rope supports part
of the load. This means that you
support part of the load. You need
less force, but you must move your
end of the rope farther. You have
to pull the rope twice the distance
the load moves. So, to move the
load 15 cm, you must pull the rope
30 cm.
In this lesson, you saw that pulleys are used in different ways.
They can change the direction of force needed. They can change
the amount of force needed—but at the cost of working longer.
This is a lot like sharing a job with others. You each do a part of
the work so it’s easier.
Turn to Assignment Booklet 1A and complete question 3 of the
Section 1 Assignment.
Section 1: Lesson 3
Copyright ©2006, Alberta Education
37
gg
Su
ested A
nsw
ers
Activity 3: Lifting the Easy Way
Part A: Fixed Pulley System
7. Measure how far the bucket lifted off the ground.
Distance the bucket lifted off the ground: about 30 cm
8. a. In which direction did you apply the force to the rope—up or down?
b. As you applied the force, in which direction did the load move?
c. When you pulled the rope, the load moved. Did the load move less, the same, or more
than the distance you pulled the rope?
You pulled down on the rope.
The load moved up.
The load moved 30 cm, the same distance the rope was pulled.
Part B: Movable Pulley System
13. Measure how far the bucket has moved.
Distance the bucket moved: about 15 cm
14. a. In which direction did you apply force to the rope—up or down?
b. As you applied the force, in which direction did the load move?
38
You pulled the rope up.
The load moved up.
Copyright ©2006, Alberta Education
Science 4: Module 1
c. When you pulled the rope, the load moved. Did the load move less, the same, or more
than the distance you pulled the rope?
The load moved about 15 cm. This is about half as far as the rope was
moved. The load moved less distance.
y Words
e
K
fixed pulley: a pulley attached to
something that does not move
pulley: a wheel-and-axle system used to
change the direction of an applied
force
load: object or material to be moved
simple pulley: a pulley with one wheel
movable pulley: a pulley that moves
with the load
a
Im
ge Credit
s
All images in this lesson were created by or for Alberta Education with the following noted exceptions:
Page
30 “© 2006 Jupiterimages Corporation”
32 “© 2006 Jupiterimages Corporation”
Section 1: Lesson 3
36 © 2005–2006 www.clipart.com
37 both: © 2005–2006 www.clipart.com
Copyright ©2006, Alberta Education
39