•
4
Pulleys
and Gears
I
Plant Growth
Magnetism
Forcesand Movement
Stability
Soil
4 ..
Habitats
Light
Sound
Pulleys and Gears
Rocks and Minerals
The Human Body
Changes in Matter
Conservation of Energy
Forceson Structures
Weather
Diversity of Living Things
Air and Flight
Electricity
Motion
Space
Addison
Wesley
ISBN 0-13-504550-9
U n i t
Coordinating & Developmental Editors
Jenny Armstrong
Lee Geller
Lynne Gulliver
Editors
Susan Berg
Jackie Dulson
Christy Hayhoe
Sarah Mawson
Mary Reeve
Keltie Thomas
Researchers
Paulee Kestin
Louise MacKenzie
Karen Taylor
Wendy Yano, Colbome Communications Centre
Reviewers
Anita Hayhoe, Brampton Christian School, ACSI
Lynn Lemieux, Sir Alexander MacKenzie Sr. P.S., Toronto District School Board
Sidney McKay, Brookbanks Education Centre, Toronto District School Board
Klaus Richter, formerly Edgewood P.S., Toronto District School Board
4
In this unit, you will learn about two special kinds of wheels: pulleys
and gears. Pulleys and gears play an important part in our lives. Even
when we can't see them, they are in machines all around us. They
help us to get where we're going (in bus and car engines, and
bicycles). They keep us on time (in watches and clocks). They make
tasks easier (in eggbeaters and cranes). They even allow us to skip
the stairs once in a while (in escalators and elevators).
Pearson Education Canada would like to thank the teachers and consultants
who reviewed and field-tested this material.
Design
Pronk&Associates
Copyright© 2008 Pearson Education Canada Inc., Toronto, Ontario
All rights reserved. This publication is protected by copyright, and permission
should be obtained from the publisher prior to any prohibited reproduction,
storage in a retrieval system, or transmission in any form or by any means,
electronic, mechanical, photocopying, recording, or likewise. For information
regarding permission, write to the Permissions Department.
The information and activities presented in this book have been carefully
edited and reviewed. However, the publisher shall not be liable for any
damages resulting, in whole or part, from the reader's use of this material.
Launch: Finding Pulleys
and Gears . . . . . . . . . . . . . . . . . . . . . 2
7: How Gears Work
23
Brand names that appear in photographs of products in this textbook are
intended to provide students with a sense of the real-world applications of
science and technology and are in no way intended to endorse specific
products.
1: Pulley Power
4
8: Gears on the Bike Go Round
and Round
27
2: Using One Pulley
7
9: The History of Bicycles
31
3: Using More Than One Pulley
10
Design Project: Design a Crane
36
ISBN 0-13-504550-9
4: How Pulleys Work
13
Unit Review
39
5: Gearing Up
16
Glossary
43
6: Gearing Up Again
20
Printed and bound in Canada.
1 2 3 - TCP - 10 09 08
Addison
Wesley
1. In a small group, list all the examples
of pulleys and gears that you see in the
illustration. How are structures used to
support the pulleys?
3. Now look at the examples of gears you
recorded. How are they similar? How are
they different?
4. What can pulleys do that gears can't do?
2. Look at the examples of pulleys you
recorded. In what ways are they similar?
For what types of tasks are pulleys often
used?
IEI SCIENCE
& TECHNOLOGY 4
Communicate
\i ~
Discuss Write ~
1. List and share any questions you have
about pulleys and gears.
2. After school, go on a pulley and gear hunt
in your own home or with a partner
around. your neighbourhood. Describe all
the examples of pulleys and gears you
find. In some cases you might not be able
to see the gear or pulley because it is
inside a machine. As long as you know the
machine contains a pulley or gear, you can
include it in your list. Combine your list of
examples with other students in your group.
Share your combined list with the class.
1!!11!1
On What You Know
Start a scrapbook. Begin by collecting
pictures of pulleys and gears or
machines that contain pulleys and gears
from magazines, brochures, and on the
Internet. Gradually, you will be adding
more pictures and your own drawings
to the scrapbook. At the end of the unit,
take your scrapbook home to share
with family members.
PULLEYS AND GEARS
Ill
1 Pulley Power
" Work On It
Safety Caution
In this activity, you will learn about how
pulleys work by designing and making a
system that will lift an object off the floor.
Materials for each group:
string
tape
scissors
paper clips
medium-sized rock
wooden dowel
empty thread spools
spring scale
bamboo skewers
ruler
straws
You have seen some of the many ways that pulleys and gears are used
in our lives. There are uses of pulleys you might not have discovered that
may surprise you. The photograph shows how a pulley system in Niger,
Africa is used to get water from a well. A wooden structure was built to
support a pulley. One end of a rope is passed over the pulley and
attached to an animal-hide bucket. By attaching the other end of the
rope to a donkey, the bucket can be raised and lowered.
This piece of equipment doesn't work by itself. Someone or something has
to pull the rope to start the motion of raising or lowering the bucket. All
motion is caused by a force. A force is a push or pum The effort needed to
pull on a rope or lift an object is an example of a force.
Ill
SCIENCE & TECHNOLOGY 4
Be careful when handling sharp tools
such as scissors and skewers.
Procedure
D Cut a piece of string about 1 m long.
Make a loop on one end. Tie the other
end of the string around the rock.
fJ Use the spring scale to lift the rock
straight up. Record the number on the
spring scale. This gives a measure of the
force you had to use to lift the rock with
your arm.
.,I
TI
·.I
I
I
..A..
PULLEYS AND GEARS
D
IJ Look at the materials that you have. With
your group, brainstorm ways you could
use the materials to build a mechanical
system that will lift the rock off the floor.
Include a pulley in your design.
I] Select the best idea from the ideas your
m
m
•
group brainstormed. Write a brief
description of the system. Explain how
you think it will work
Build your system and use it to lift the
rock Using a spring scale, measure and
record the force needed to lift the rock
Notice the direction of the force.
Change your system or select another
idea to test. Record your new idea and
build the new system. Using a spring
scale, measure and record the force
needed to lift the rock Did it take less
force to lift the rock than it did with the
first system? Was the force in the same
direction?
Communicate
2 Using One Pulley
Write Discuss Present
1. What mechanical systems did you create
to lift the rock?
2. Which system required the least effort to
lift the rock? Draw a picture of it. Why
did this system work best? How did the
structure help with the task?
3. Did your system allow you to change
the direction of the force by pulling down
on the pulley rope? Explain how this is
helpful in lifting a load.
4. Present and compare the results of your
investigation with those of other groups.
How were the systems you developed
different from theirs? How were they the
same?
You have investigated. what a pulley is, how it
works within a structure, and the different ways
that spools and string can be put together to
form a pulley system. You may have discovered.
that some pulley systems can reduce the force
needed to lift an object. Others can only change
the direction of the force. They let you pull
down on the pulley rope rather than lifting up.
In this activity, you will compare the ways that
a single pulley can be used to lift a load.
5. If you were to try this activity again,
what changes would you make to your
mechanical system to improve the way
it lifted a load? Explain.
·,· . .
v,
,J .••
On
In Pulley Power, you used thread spools,
string, and bamboo skewers to build a pulley
system. These materials were not made for
this use. Because of this, there is a lot of
friction between the spool and the skewer,
and between the spool and the string.
Friction is a force that slows down motion.
It occurs when two objects rub together.
Because friction works against movement,
it increases the amount of force you have to
use to get the pulley to work
In this activity, you will use commercial
pulleys, which create less friction than the
pulleys you have created.
•
SCIENCE & TECHNOLOGY 4
------
Fixed Pulley System
In this activity, you'll be using a fixed pulley
system to lift a load. In a fixed pulley system,
the pulley is attached to a structure and does
not move.
Materials for each group:
pulley
ruler
string
metre stick
spring scale
2 chairs
load - a 200 g mass, or a book
PULLEYS AND GEARS •
fJ Attach the load to the pulley.
Procedure
O Cut a piece of string and tie it to the
load. Attach the spring scale and pull up
to measure the force needed to lift the
load straight up with your arm. Record
the force.
3. With a movable pulley, does it take less
force to lift the load than with the fixed
pulley?
fJ Use another piece of string to tie the
4. With a movable pulley, how is the
direction of the force needed to lift the
load different than without the pulley?
pulley to the metre stick Make sure the
pulley can turn easily. Balance the metre
stick over the backs of two chairs to
keep the pulley firmly in place.
5. When would you use a fixed pulley to lift a
heavy object? When would you use a
movable pulley to lift a heavy object?
m
•
II
With a smooth motion, lift the load by
pulling up on the spring scale.
Remove the load and untie the pulley
from the metre stick Keep your materials
for use in the next part of this activity.
In this activity, you'll be lifting a load using a
movable pulley system. In a movable pulley
system, the pulley supports the load and is
not fixed in place.
Materials for each group:
Place a 1 m piece of string in the pulley
groove. Tie a loop at one end of the
string.
I) Tie one end of the string around the load
m
•
and connect the looped end to the
spring scale. Lift the load by pulling
down on the spring scale with a smooth
motion.
How much force do you need to lift
the load? Were you pulling in the same
direction as when you lifted the load
in step l?
SCIENCE & TECHNOLOGY 4
Use the materials from the Fixed Pulley
System activity
I) How much force do you need to lift the
Procedure
Tie one end of the string that passes
through the pulley groove to the metre
stick Balance the metre stick over the
backs of two chairs. Connect the other
end of the string to the spring scale.
6. Compare the commercial pulleys you
used in this activity with the "homemade"
pulleys used in Pulley Power. Which
materials would you rather work with?
Why?
7. Look back at the list of pulleys you
observed in Finding Pulleys and Gears
on pages 2 and 3. Which pulley systems
do you think are fixed and which are
movable? Which type of pulley is more
common? Did you find any pulley system
that was different from the two you
investigated in this activity?
Movable Pulley System
II
2. With a fixed pulley, how is the direction of
the force needed to lift the load different
than without the pulley?
8. Look at the structures that hold the
pulleys in the illustration on pages 2 and 3.
What role does the structure play in these
pulley systems?
load this time? Were you pulling in the
same direction as when you lifted the
load without a pulley?
Communicate
Write
1. With a fixed pulley, does it take less force
to lift the load with the pulley or without a
pulley?
Try to find a picture of a machine with a
single fixed pulley and one with a single
movable pulley. Or, draw a picture of
each type of pulley. Add these pictures
to your scrapbook, and for each picture,
write a brief description of how the
pulley works .
PULLEYS AND GEARS
D
3 Using More Than
One Pulley
Can you imagine a pulley system that
involves both a fixed pulley and a movable
pulley? What about a system that has two
fixed pulleys and one movable pulley, or one
fixed pulley and two movable pulleys? How
would these systems work? In this activity,
you'll get a chance to find out.
Materials for each group:
single pulleys
spring scale
double pulleys
ruler
triple pulleys
metre stick
string
2 chairs
load -
200 g mass, or a book
Procedure
D With your group, plan an investigation
to determine how well different pulley
systems work to raise a load. Make sure
your investigation is a fair test. To ensure
it is a fair test, you must keep all the
conditions of the investigation the same
except for the variable you are testing.
Variables include the size of the load and
the number of pulleys. How will you
make sure your test is fair?
fJ Look at the materials you have. With
your group, brainstorm ways to use
these materials to lift the load off the
floor using the least force. As you
brainstorm, think about the differences
between fixed and movable pulleys.
IJ Design several systems that combine
both types of pulleys in different ways.
Then choose one system that you think
will lift the load with the least force.
Why do you think it will lift the load
using the least force?
I) Write a detailed description
of what
your system looks like and how it
works. How will you attach the pulleys
to a structure so they are stable?
~tarted
You now know what a pulley is and how it works. You have used both
fixed and movable pulleys. You compared the pulley systems you have
built to those you have seen around you. Did you notice that machines
often link several pulleys together? In this activity you'll investigate
combined pulley systems (sometimes called block and tackle).
I
Commercial pulleys are available that have two or three wheels joined
together. Some are joined with one pulley in front of the other, while others
are joined with one pulley above the other. If they are available, you will
use double and triple pulleys in this activity. You can use as many or as
few of the wheels on each pulley as you wish.
m
SCIENCE & TECHNOLOGY 4
PULLEYS AND GEARS
m
m
Build your system and use it to lift the
load 10 cm above the floor. Measure and
record the force needed to lift the load.
Communicate
1 ~·
Write
Discuss
1. Share your investigation and results with
another group. Explain your experiment
and answer any questions your classmates
have. Look at your classmates'
investigation. How did they make sure
that their investigation was a fair test?
2. How do the results of your investigation
help you to understand how well different
pulley systems move a load? Why did
some systems work better than others?
3. What happens to the force needed to lift
the load when you use more than one
pulley? Explain.
4. What happened to the direction of the pull
when you used more than one pulley?
m
Select another system to test. Record
your idea and build your new system.
Did it need more or less force than the
first system to lift the load?
4 How Pulleys Work
.
In your investigations so far, you
have discovered that pulleys can
be used to reduce the force needed
to lift a load. Now it's time to learn
more about how pulleys work. As
you read through this information,
keep a list of any words that are
new to you.
5. Which arrangement of pulleys used the
least force to lift the load with your pulling
down?
6. Which arrangement used the least force
with your pulling up?
7. Describe any place or places where you
have seen two pulley systems used
together.
I;$ n I On What You Know
Find a picture of a machine that uses
more than one pulley. Or, invent a
machine of your own with several
pulleys and draw a picture of it. Add the
picture to your scrapbook. Describe
how the machine is used.
You've learned that the effort
needed to lift an object is an
example of a force. Gravity is
also a force. It acts on all objects
on Earth-including you-attracting
them toward the ground. Gravity
keeps you from floating into space!
The weight of an object is a measure of the
force of gravity acting on it. This is called the
load force. In order to lift an object, you
must work against the force of gravity. This is
called the effort force.
>SSS-
I.
...
••
A fixed pulley can help you lift a load by
allowing you to pull down on a rope. Pulling
down is easier than lifting up a load by yourself. Imagine you had to move a refrigerator
to the third floor of a building. Using a pulley
to lift the refrigerator is much easier than
carrying it up three flights of stairs!
The comparison of the load force to
the effort force needed to lift the load
is called the mechanical advantage.
'
m
SCIENCE & TECHNOLOGY 4
PULLEYS AND GEARS
m
COMBINED PULLEY
FIXED PULLEY
With a fixed pulley, when
you pull down on the
pulley rope, the load
moves up. A fixed pulley
changes the direction of
the effort force. This
means that you can use
your whole body to pull
down to lift the load.
With only one pulley,
however, the effort force
is equal to the weight or
load force of the object.
Motion
Effort Force
l
Load Poree
A combined pulley
system uses both a fixed
pulley and a movable
pulley. The fixed pulley
in this system changes
the direction of the
effort force. This allows
you to pull down to lift
the load. The movable
pulley in the system lets
you pull using only half
the effort force. This is
because the pulley rope
takes half the weight of
the load.
A single fixed pulley changes the direction of the effort force. But
you must use the same amount of effort force to pull as you would if
you were lifting the load without a pulley.
Effort Force
Motion
i
Load Force
A single movable pulley does not change the direction of the effort
force. But you need to pull with only half the effort force you would
use with a fixed pulley or with no pulley at all.
m
SCIENCE & TECHNOLOGY 4
,I
L.
With a single movable
pulley, the pulley is
attached to the load and
the rope is attached to
the ceiling. To lift the
load, you pull up on the
other end of the rope.
So, the effort force is in
the opposite direction
to the load force. The
benefit of a movable
pulley is that you only
have to pull with half
the effort force to lift
the load. This is because
the rope attached to the
ceiling takes half the
weight of the load.
Motion
l
Load Force
A combined pulley system has the benefits of both a fixed and a
movable pulley-you pull down and use only half the effort force
you would need to lift the load without a pulley.
A pulley system makes it easier to lift a load
because it can
Communicate
a. change the direction of the force
needed to pull (fixed pulley)
1. What is the advantage of a single fixed
pulley system?
b. reduce the force needed to pull
2. What is the advantage of a movable pulley
system?
(movable pulley)
c. change the direction of the force
needed to pull and reduce the force
needed to pull (combined pulley)
Write
3. What is the disadvantage of a movable
pulley system?
4. Look at the picture of the combined pulley
system. What type of pulley is the upper
pulley? The lower pulley?
5. What are the two advantages of a
combined pulley system?
PULLEYSAND GEARS
m
5J Gearing Up
~
Up to now, you have used pulleys to transfer movement. Another way
to transfer movement is to use gears. Gears have interlocking teeth that
connect with and move each other.
How does the number of teeth on a gear
system affect the speed and direction of its
motion? Investigate gears in this activity to
find out.
Safety Caution
Always wear your safety goggles when
working with sharp objects such as nails.
.
m
SCIENCE & TECHNOLOGY 4
Materials for each group:
2 corrugated cardboard sheets
scissors
finishing nails
safety goggles
Trace theses gears to make your own.
PULLEYSAND GEARS
ID
Procedure
D Trace each of the gears shown onto
separate pieces of paper. Cut out each
gear and trace around or glue them
onto one of the cardboard sheets.
Mark the centres, then carefully cut
out the gears to make two small gears,
one medium gear, and one large gear.
Colour one tooth on each gear to help
you count the number of times the gear
turns.
lr:I
U
1st
Drscnon
Gear
1t turns
I ofNumber
I gear
:2nd
turns
small
small
small
medium
small
large
Drecnon
1t turns
I Number
medium gear. Pin the medium gear in
place so that the teeth interlock with the
small gear. Turn the small gear.
Wearing your safety goggles, push a nail
through the centre of each gear. Use the
nail to attach one small gear to one of
the cardboard sheets. Pin the second
small gear next to it so that the teeth
interlock.
b. If you turn the small gear six full
turns, how many times does the
medium gear turn? How can you tell?
b. If you turn the small gear six full
turns, how many times does the large
gear turn? How can you tell?
fJ Suppose you were to turn the large gear.
m
•
m
Replace the medium gear with the large
gear. Pin the large gear in place so that
the teeth interlock with the small gear.
a. Turn the small gear. What happens to
the large gear? What direction does it
turn?
a. What happens to the medium gear?
What direction does it turn?
turn? If you turn the first gear one full
turn, how far does the second gear turn?
How can you tell? Use a chart like the
one shown to help organize your
observations.
SCIENCE & TECHNOLOGY 4
m
I) Replace the second small gear with the
IJ Turn
the first gear. What happens to the
second gear? What direction does it
m
of turns
For each full turn, predict if the small
gear will turn more than one, less than
one, or exactly one full turn. Use the
materials to check your prediction. Tum
the large gear twice. How many times
does the small gear turn?
Experiment with other gear
combinations and with three gears
connected together. What conclusion
can you make? Save your gears for
use in the next activity.
Communicate
.• i
.........................................
Discuss Write
1. What do you notice about the direction of
movement of each pair of gears?
2. Count the number of teeth on each gear.
How does the number of teeth on each
gear affect the number of turns you get
with different pairs of gears?
3. Suppose the first gear in a system has ten
teeth. How many teeth should the second
gear have if you want to get one turn from
it for every three turns of the first gear?
Explain.
4. Where might gears be used?
I :mj n I
I
On What You Know
Find photographs of real-life machines
that use gears. Or, design your own
imaginary machine with gears and draw
a picture of it. Add the photographs or
drawing to your pulleys and gears
scrapbook. Include as much
information as you can about what the
machine is used for and how it works.
Suppose you were to turn the medium
gear. For each full turn, predict if the
small gear will turn more than one, less
than one, or exactly one full turn. Use
the materials to check your prediction.
Turn the medium gear four times. How
many times does the small gear tum?
PULLEYS AND GEARS
m
6 Gearing Up Again
Safety Caution
In this activity, you'll investigate whether
the cardboard gears you created in the last
activity will work if they meet at an angle.
How will motion be transferred? Will the
same relationships hold between the number
of teeth on each gear and the number of
turns?
Materials for each group:
cardboard gears from Gearing Up
corrugated cardboard sheet
finishing nails
safety goggles
Be very careful when handling sharp
objects. Remember to protect your eyes!
Procedure
D Wearing your safety goggles, push one
nail through the centre of each gear.
fJ the
Fold the corrugated cardboard sheet in
middle and hold it as shown below.
Pin one small gear onto the vertical part
of the cardboard near the bottom. Pin
the other small gear onto the horizontal
part of the cardboard. The teeth of both
gears should interlock.
Optional Materials:
thin cardboard sheet
Water wheel
Started
The gears you have investigated work on a flat or horizontal surface.
They are called spur gears. Sometimes, machines contain gears that
meet at an angle. If the first gear is vertical (upright) and the second is
horizontal, we say the gears meet at a right angle. The vertical motion of
the first gear is changed to the horizontal motion of the second. Gears
that meet on an angle are called bevel gears.
In old-fashioned mills, systems of gears were used to change the vertical
motion of a waterwheel to the horizontal motion of millstones for grinding
grain. Falling water was used to turn a large wheel. As this wheel's axle
(a bar or rod connected to the wheel) turned, it set in motion a series of
gears and pulleys. In some mills, these included bevel gears as shown
above.
m
SCIENCE & TECHNOLOGY 4
•
PULLEYS AND GEARS
m
7 I How Gears Work
IJ Tum the vertical gear.
a. What happens to the horizontal gear?
b. If the vertical gear is turning clockwise, in which direction does the
horizontal gear turn?
c. For each full turn of the vertical gear,
how many turns does the horizontal
gear make?
If Time Allows
Replace the corrugated cardboard
gears with similar gears made of thin
cardboard. Predict how this gear system
will work compared to the previous
system. Will thinner, more flexible gears
work as well as sturdy, thick gears?
Check your prediction.
Communicate
'"' "'
Write Discuss
Discuss these questions with a partner.
1. What is special about this type of gear
system? When might it be used?
2. Draw a picture of a gear system that
would change the direction of motion
m
SCIENCE & TECHNOLOGY 4
from vertical to horizontal, and for which
every turn of the vertical gear would result
in two turns of the horizontal gear.
3. What effect do different materials have on
gear operation? Why do you think gears
are usually made of metal? What would
happen if gears had to be made of other
materials, such as wood?
_)
]
___J
$tarted
You have already learned a lot about gears. Like pulleys,
gears can be used to transfer forces and motion from one
object to another. Some gear systems, like the ones you've
worked with, can also be used to change the direction of
the motion. As you read, create a mind map of terms
related to gears.
Remember,you can recycle your
card.board when you are finished
with it.
Research to find examples of real-life
machines that use pulley and gear
systems together. Draw the machines.
Or, design and draw your own imaginary machine that uses pulleys and
gears. Describe how the turning motion
of one system is transferred to a turning
motion in the other system. Add the
drawing and description to your
scrapbook.
[- ~
l
J
I
Most gears are flat wheels with teeth around
their edges or grooves along their sides. Some
gears have other shapes, like cylinders and
cones, with teeth or grooves cut into them.
Gears are usually attached to axles or shafts
and are used to transfer circular motion from
one shaft to another within a machine. In
doing this, gears can change the direction of
the force. They may also change the strength
of the force.
PULLEYS AND GEARS
m
When two interlocking gears have the same
number of teeth, they turn at the same speed,
but in opposite directions.
When two gears have different numbers of
teeth, they turn at different speeds. If a small
gear turns a large gear, the small gear must
turn more than once to cause the large gear
to complete one turn. So, the large gear turns
more slowly than the small gear. In this way,
gears can be used to change the speed of
motion.
In Gearing Up, you created spur gears. In spur
gears, the teeth meet on a flat surface and can
change the speed and direction of motion.
What do you think would happen to the small
gear if the large gear is turned? If the large
gear is turned, the small gear turns in the
opposite direction and at a faster speed!
In Gearing Up Again, you created a form of bevel
gear. Your bevel gears were flat wheels, but bevel
gears are often cone-shaped. In bevel gears, two
gears connect at an angle. They can also change
the speed and direction of the motion.
Two equal-sized gears
To keep the direction of the motion the same,
you need to use three gears. In a three-gear
system, the second gear changes the
direction of the motion. The third gear
changes the direction of that motion again,
and moves in the same direction as the first
gear. When you put many gears together it
is called a gear train.
Spur gears are used in car transmissions.
Two different-sized gears
Bevel gears are used in egg beaters.
There are many types of gears designed
for different purposes. They differ in the
arrangement and type of teeth, the way
the axles are put together, and the angle
at which the teeth meet.
Three equal-sized gears
m
SCIENCE & TECHNOLOGY 4
In worm gears, an axle or shaft has a screw thread
that connectswith another gear. This system is
often used to reduce the speed and change the
direction of the motion.
Worm gears are used in electric mixers.
PULLEYS AND GEARS
m
8 Gears on the Bike Go
In rack and pinion gears, a single gear, called the
pinion, meets with a toothed rack. The rack may slide
or stay in one place. The system changes circular
motion into motion in a straight line. When railroads
are built on very steep hills, they may use rack and
pinion gears to help keep the train on the tracks.
Round and Round
Rack and pinion gears are used in a cogwheel railway.
Communicate
Write
1. When two gears connect, in what direction
does each gear turn compared to the
other?
2. If three gears are connected in a gear
train, in what direction does each gear
turn compared to the others?
5. Imagine you want to turn a crank that is
very difficult to turn. You can use a small
and a large gear to connect the crank to
the handle that you turn. Does the small
gear go on the crank axle or on the handle
you turn? Does the large gear go on the
crank axle or the handle?
3. Describe how gears operate when they
connect on a flat surface and when they
connect on an angle.
4. Look around your school, home, and
community for examples of each kind of
gear system-spur gears, bevel gears,
worm gears, and rack and pinion gears.
Started
So far, you've investigated gears and how they work, and you have
looked for machines that use gears. There is one machine with gears that
you may know well-a bicycle. Bicycles have sprocket and chain gears
that work like some pulley systems. A chain connects the sprocket gears
on the pedals to the back wheel. The chain also allows the gears to turn
in the same direction. The sprockets keep the chain from slipping as it
turns. What do gears do for a bicycle and for a bicycle rider? To find out,
you'll be looking more closely at the gears on a bicycle.
In your scrapbook on pulleys and gears,
try to describe a machine that uses each
of the gear systems described. Make a
sketch of each machine and note the
type of gear it uses.
a. Which gear system appears to be most
common? Give a reason why.
b. Were gear systems easy or difficult to
find? Explain.
m
PULLEYSAND GEARS
SCIENCE & TECHNOLOGY 4
L
m
Number of
gear teeth on
front sprocket
Number of
gear teeth on
back sprocket
Number of
pedal turns
Low gear
1
High gear
I
I) When the chain passes around a large
back sprocket, the bicycle is said to be
in low gear. Put the bicycle in a low
gear. Count the number of gear teeth
on the front and back sprockets that
you are using. Record your observations
in a table like the one shown above.
Low gear
II
. ··ork On
For this activity, you'll need to use a bicycle
that has different gears. These are sometimes
called 3-speed, 5-speed, and so on, depending
on the number of gear combinations they have.
Materials for each group:
bicycle with gears
paper
tape
scrap piece of wood
m
SCIENCE & TECHNOLOGY 4
Procedure
D Turn the bicycle upside-down
so that it
rests on its handle bars and seat. Tape a
small piece of white paper on the back
tire as a marker.
fJ The gears on a bicycle are called
sprockets. Look at the back sprockets.
How many are there? How are these
sprockets similar to each other? How
are they different?
m
Use a scap piece of wood to apply
friction to the back wheel. Turn the
pedal one complete turn while you
observe the back wheel. What happens?
Notice the force needed to turn the
pedal in order to get the back wheel
turning in low gear.
Number of
back wheel
turns
m
•
1
When the chain passes around a small
back sprocket, the bicycle is said to be in
high gear. Put the bicycle in a high gear.
Again, count the number of gear teeth on
the front and back sprockets that you
are using. Record your observations in a
table like the one shown above.
High gear
IJ back
Repeat step 4. How many turns does the
wheel make in one complete pedal
m
turn? Record your observations in the
table.
Notice the force needed to turn the
pedal to get the back wheel turning in
high gear. How does this force compare
to the force needed in low gear?
Safety Caution
Turn the pedal slowly and keep your
fingers away from the wheel spokes.
PULLEYS AND GEARS
m
Communicate
.........................................
Discuss Write
Discuss the following questions with your
group.
1. Why do you think there are different
sprockets attached to the pedals, and
other sprockets attached to the back
wheel?
2. Which gear is best for going up a steep
hill? Why?
3. Which gear is best for travelling the fastest
on flat ground? Why?
4. Why aren't the gears and chain painted?
Explain.
5. What material is put on the gears and
chain of a bicycle to make them work
better?
6. Look at another mechanism on the
bicycle-the brakes. Describe what
happens when you squeeze the brakes.
How do they work to slow down the
bicycle?
9 The History of Bicycles
~~
7. Can you find any examples of pulleys on
the bicycle?
8. How does the structure of a bicycle allow
mechanical systems such as gears to
work?
Make a sketch to show how the gears
and chain of a bicycle look in low and
high gear. Explain how the number
of teeth on the sprockets affects the
turning of the wheels and the bicycle's
motion. Add your sketch and
information to your scrapbook.
•
Started
In the last activity I you learned that the way a bicycle1s sprocket and
chain gear system works depends on the size and number of teeth of the
two sprockets in use. You know that in any pair of wheels joined by a
belt or chcdn, the larger wheel will rotate more slowly than the smaller
wheel. The bigger the difference in size between the two wheels, the
bigger the difference in speed.
The gear shifter of a bicycle allows the rider
to change the sizes of the sprockets being
used. In low gears, the back sprocket is large.
This means that the back tire will rotate
fewer times for one pedal turn when
compared to higher gears. But, you need less
force to make the pedal turn. This is useful
for climbing hills. In high gears, the back
sprocket is small. The back tire will rotate
more times for one pedal turn when
m
SCIENCE & TECHNOLOGY 4
compared to lower gears. This means the
bicycle travels farther with each pedal turn,
which allows you to go faster on level
ground. But, you must use more force to
make the pedal turn.
Today, we take it for granted that a bicycle
has a chain, pedals, gears, brakes, and rubber
tires. But the earliest bicycles lacked most
of these items. When were bicycles first
developed? How have they changed over the
PULLEYS AND GEARS
m
years? What might the bicycles of the future
look like?
As you read through this information about
bicycles of the past, present, and future,
work with a partner to develop a timeline of
the history of the bicycle. At each stage of
the timeline, record what you think are the
most important features of the bicycle.
The first known bicycle, called the
Draisienne, was built and used in Paris in
1817 by Baron von Drais. But it was very
different than today's bicycle. It had two
wheels of equal size that could turn but the
bicycle always faced straight ahead. Between
the wheels was a frame on which the rider
sat. This bicycle was made entirely of wood.
The rider made the bicycle move by pushing
his feet along the ground.
In the second version of this bicycle, von
Drais changed the design so that the front
wheel could be turned to the left or right to
steer the bicycle.
Later models of the bicycle such as the
"penny-farthing", created by James Starley in
1870, were made with a large front wheel and
a small back wheel. The larger the front
wheel, the farther the bicycle travelled with
every turn of the pedal. This meant that the
rider did not have to pedal so fast to keep
moving. However, these bicycles could be
dangerous as they tipped easily when riding
over uneven road surfaces.
The next major innovation occurred in 1865
when a machine known as the Velocipede
became popular. It was invented in 1861 by
two Frenchmen named Pierre Michaux and
his son Ernest. The rider used his feet to turn
pedals attached to the machine's large front
wheel.
The first models of the Velocipede were
made of wood, but later models had metal
tires. They were heavy, difficult to steer, and
could reach only limited speeds. Despite this,
they became popular. In large cities, indoor
riding rinks were set up. Models were even
developed that could be used on ice!
The name Velocipede means "fast foot". The
machine was also known as the "bone shaker"
becauseof the discomfort of riding it on bumpy
cobblestone roads.
By the 1870s, the first all metal machines
with solid rubber tires were produced. Their
design resembled the Velocipede. They were
the first machines to be called bicycles. The
word bicycle means "two wheels."
For a time in the late 1800s, adult-sized
tricycles were popular. These tricycles could
also be used by women, whose long skirts
made it difficult to ride the high wheelers.
Many of the mechanical systems invented
for these tricycles were later used by the
automotive industry. Two examples are hand
brakes and the rack and pinion steering
systems.
This tricycle from 1882 is called the Royal Salvo.
Unlike the high wheelers, the tricycle's pedals
were not attached directly to the wheel.
The Draisienne,or "swift-walker" as it was also known, was practical only for use on well-maintained pathways.
m
SCIENCE & TECHNOLOGY 4
The penny-farthing was also known as the "high
wheeler" becauseof its large front wheel.
By the 1890s, air-filled tires and a sprocket
and chain gear system were introduced. The
air-filled tires made the ride comfortable. The
gears allowed people to travel as far with
each pedal turn as with the high-wheeled
bicycles, but without the need for a giant
wheel.
PULLEYS AND GEARS
m
Bicycles looked much as they do today, with
equal-sized wheels and a metal frame. They
were more comfortable and safer than ever
before. The bicycle was on its way to being
used widely around the world.
Canada's first "homegrown" wide-tire mountain
bike was created by Vancouver's Rocky Mountain
BicyclesLtd. in 1982. The RM9, shown, is their
latest downhill race weapon.
Two unusual types of modern bicycles are
recumbent bicycles, which allow the rider
to sit back, and Para-cycles TM. To drive a
recumbent bicycle, you sit lower down, in
a more comfortable position, with a backrest
behind you. The pedals are in front of the
wheels rather than between them.
This circa 1896 advertisement from Massey-Harris
shows the variety of bicycle styles available.
Bicycles are now one of the world's most
popular forms of transportation. Today, there
are about 800 million bicycles in the world.
This is twice the number of cars. The number
of bicycles made every year is about three
times the number of cars made.
Many specialty bicycles have been built, such
as mountain bikes, BMX bikes, freestyle
bikes, racing bikes, touring bikes, and
tandem bikes (bicycles for two riders).
The Para-cycle TM is modelled on a recumbent
bicycle frame but it has three wheels. It can
be driven on the road like a bicycle, but can
also fly in the air like a powered parachute!
For take-off, it can climb at a rate of 150 m
each minute with an 80 kg pilot. Are these
examples of the bicycles of the future?
Communicate
1 ~}.
Write Discuss
Discuss the following questions with your
partner.
Recumbent bicycles hold many speed records,
although they are usually banned from racing.
4. Study the way your city or town is laid
out. What would you change if you wanted
to encourage more people to use bicycles
as their main type of transportation?
The Para-cylce™has an engine, removable power
pack, and lifting parachute.
2. Which of the developments on your
timeline did the most to make bicycles
a practical and popular form of
transportation? Why? Were you able to
convince your partner of your choice?
l. What were the results of having a limited
choice of materials when building early
bicycles, for example, using metal tires
instead of rubber, and using wood or metal
frames instead of the light steel frames
used today?
3. a. List some of the advantages of bicycles
over cars.
Design a new bicycle. How would you
modify current bicycles to make one
that is better or more fun to ride? What
new parts would you add? Create a
poster to advertise your new bicycle
and explain its special features. Add
this poster to your scrapbook. Take
your scrapbook home and share it with
family members to demonstrate what
you have learned about pulleys and
gears.
b, List some factors that limit the use of
bicycles. Can you think of ways to
overcome any of these factors?
Try to make your lists as complete as
possible.
m
SCIENCE & TECHNOLOGY 4
PULLEYS AND GEARS
m
Design
Project
The pulley and gear systems you decide to
build for your crane can be similar to the
ones you have studied, or they can be new
systems that you make just for this
project. Look at the cranes shown, and at toy
cranes if they are available, to get an idea of
how cranes work As you work on your crane
design, consider the following questions.
• What are the main parts of a crane?
• What types of movements do they make?
• How might you recreate these movements
in a model crane?
• How do gears and pulleys help cranes
work?
Think about what materials you might use to
build a working model. To help get you started,
some possible materials are listed. You don't
have to limit yourself to these suggestions!
Materials for each group:
pictures of cranes and toy cranes for
reference
pencils
paper
a variety of building materials such as
plastic straws, boxes, craft sticks, paper
fasteners, string, wire, cardboard, bamboo
skewers, empty thread spools, wooden
blocks, cardboard rolls from paper towels
and toilet paper, glue, tape, scissors
~-
.~
m
SCIENCE & TECHNOLOGY 4
it
~-~
- - ... ..
-
-_
.
~·~
~~- -~ ---~·s
PULLEYS AND GEARS
m
Design
Project
Procedure
D Brainstorm
ideas with your group for
the kind of crane you want to build. You
could copy a crane you've seen, modify
a crane you've seen so that it will work
differently, or design a new one. Choose
the best idea from your list.
I) Once you have finished your model,
g
test it. Can it complete the tasks you
intended? If not, try to think of ways to
improve the crane.
Demonstrate
What You Know
Make a detailed drawing of your finished
crane.
Get Started
fJ Once you have decided on an idea, make
a detailed drawing of your crane.
Describe what tasks your crane can be
used for and how it works. Be sure to
explain how the pulleys and gears help
it to work Think about how you might
create these parts and movements in a
model.
iJ Decide
what materials you will need.
Work together to gather the materials
and build your model crane. You may
need to make changes to your design if
you can't find some of the materials you
need.
Communicate
Present Write
Now it's time to show how much you have learned about pulleys
and gears. Read over what your tasks ere, and talk to your
teacher if you are unclear about what to do.
Discuss
1. Present your group's crane to the class.
Share your design sketches, demonstrate
the tasks your crane can perform, and
explain how the pulleys and gears help it
to complete these tasks.
2. As you watched the presentations of other
groups, you may have thought of ways to
modify your own crane. What would you
change about your crane if you were to
build another model? Explain why you
would make these changes.
Work On It
1. Sarita and Catherine share a tree house in
Sarita's backyard. To reach the tree house,
they climb a rope ladder. They want to
bring Catherine's pet dog into the tree
house but the dog cannot climb the rope
ladder. Neither girl can climb the ladder
while carrying the dog. They decide to
make a mechanical system that would use
pulleys and/or gears to lift objects up to
their tree house.
2. Sketch a design for the mechanical
system, clearly label all the parts, and list
the materials you would use to build it.
3. Write a description explaining how the
system uses pulleys and/or gears to lift
objects up into the tree house.
4. Now check your work
My design uses a system of pulleys
and/or gears to lift objects.
3. Machines, such as cranes, that help people
do work may damage the environment. In
what ways might a crane change or harm
the environment?
4. Discuss with your classmates the kinds of
materials you would probably use if you
were to make a real crane. How would the
materials that were available affect the
crane's use? For example, what would
happen if you had to use wooden pulleys
instead of metal ones?
m
SCIENCE & TECHNOLOGY 4
My design has a labelled sketch, and
a materials list.
My description clearly explains how
my design works.
~
My design and description show how
pulleys and/or gears can be used to
move objects.
PULLEYS AND GEARS
m
• ~ -~
_i
.t .. ~- ....
;-: .-.. ~-.
:;:
l~Review;·_----------J------------------,
Explain
Communicate
Now it's time to think about how well you did. Use this chart to help you score your work
Four stars is the highest score for each.
1 Star
}r
2 Stars
)< /(
4 Stars
3 Stars
\
/(
\
/(
\
/(
\
\
\
,r( /(
.:
.:
\
• How much do you know about pulleys and gears? Look at your labelled sketch, list of
materials, and description. Does your work show you know
A little about
pulleys and gears
Some
information
about pulleys and
gears
A lot of
information
about pulleys and
gears
All about pulleys
and gears?
• Look at the description of how your design works. Does your work show you have applied
A few of the skills
to use pulleys and/or
gears to lift
objects
Some of the skills
to use pulleys and/or
gears to lift
objects
Most of the skills
to use pulleys and/or
gears to lift
objects
All of the skills to
use pulleys and/or
gears to lift
objects?
• Now look again at your description. Will a reader find your description
Not very clear
or precise
Somewhat clear
and precise
Mostly clear
and precise
Very clear
and precise?
• How much understanding does your design show you have of how pulleys and gears can
be used to move objects?
Not much
understanding
Some
understanding
A good
understanding
A complete
understanding
Your Stuff
b. You have five gears connected in a gear
train. If you turn the first gear in a
clockwise direction, in what direction
will the last gear turn?
What did you learn about
pulleys and gears?
1. a. Give two examples where a pulley
system is used in everyday life.
b. Give two examples where a gear
system is used in everyday life.
2. Use a sketch to help describe an example
of each of the following systems. Include
an explanation of the forces and motion in
the system.
a. fixed pulley system
b. movable pulley system
c. combined pulley system (block and
tackle)
3. Would you use a fixed pulley or a movable
pulley to lift a heavy load of roofing
materials to the roof of a building?
Explain .
•
4. a. You have a system of two interlocking
gears. If you turn one gear in a clockwise direction, what will happen to the
other gear?
5. The first gear in a gear system has 12
teeth.
a. Describe the gear you would use with
it, if you wanted the second gear to
turn three times as fast as the first gear.
b. Describe the gear you would use with
it, if you wanted the second gear to
turn half as fast as the first gear.
6. Explain the difference between a high gear
and a low gear on a bicycle. What is the
advantage of each gear?
7. If you could investigate one question
about pulleys and gears, what would it be?
How would you investigate it?
Write a short note explaining how well you think you did.
m
SCIENCE & TECHNOLOGY 4
PULLEYS AND GEARS
m
t
Glossary
I
'1
How Did
You Do?
• A fixed pulley changes the direction of the
effort force used to lift a load.
axle a bar or rod connected to the centre of a
wheel
1. List three things that you didn't know
before completing this unit.
• A movable pulley reduces the amount of
effort force needed to lift a load. But it
does not change the direction of the effort
force.
2. What activity did you like the best in this
unit? Why? Which was your least favourite
activity? Why?
• When fixed and movable pulleys are used
in combination, they change the direction
of the effort force and reduce the amount
of effort force needed to lift a load.
block and tackle a combined pulley system
used to lift heavy objects; changes the direction
of the effort force and reduces the amount of
effort force needed to pull to lift a load
3. Give yourself three compliments about
the way you participated in this unit on
pulleys and gears. What did you do well?
• When two interlocking gears have the
same number of teeth, they turn at the
same speed but in opposite directions.
cone an object shaped like a funnel without the
tube; it has a circular base and curved surface
that comes to a point
4. List three questions that you would like to
answer the next time you study pulleys
and gears.
• When two interlocking gears have
different numbers of teeth, they turn at \
different speeds. The gear with more teeth
turns slower.
cyllnder an object shaped like a can; two
circular ends joined by a curved surface
Now you know a lot about
pulleys and gears! Here are
some things you've learned:
• Pulleys and gears can be used alone or in
combination in machines that make our
lives easier.
• Pulley systems and gear systems can be
modified to improve the way they move a
load.
• Multi-speed bicycles have sprocket and
chain gears. In high gear, each turn of the
pedals causes the bicycle to move farther
than in low gear. However, it takes more
effort to pedal in high gear.
• There are many mechanical systems on a
bicycle that help it work. These have
changed greatly since the first bicycles
were produced to make today's bicycles
more efficient.
bevel gears gears that meet at an angle; they
can change the speed and direction of motion
effort force the force required to work against
the force of gravity to lift a load
fixed pulley the pulley is attached to a
structure and does not move; changes the
direction of the effort force used to lift a load
force a push or a pull
friction a force, caused by objects rubbing
together, that slows moving objects
gear a wheel with teeth around its edge that
interlocks with the teeth of other gears
gear train a group of two or more gears
working together
gravity the force attracting all objects on Earth
toward the ground
horizontal flat; parallel to the ground; straight
across
load force the weight of an object
low gear when the chain on a bicycle passes
around a large back sprocket
movable pulley the pulley supports the load
and is not fixed in place; reduces the amount of
effort force needed to pull to lift a load
mechanical advantage the comparison of
the load force to the effort force needed to lift an
object
pulley wheel with a grooved rim and a rope,
belt, or chain that passes around it
rack and pinion gears a gear system in which
a single gear (the pinion) meets with a toothed
rack, which slides or stays in one place; changes
circular motion into motion in a straight line
sprockets the gears on a bicycle
sprocket and chain a gear system in which a
chain connects the gears to transfer motion (as
on a bicycle)
spur gears gears that meet on a flat or
horizontal surface; can change the speed and
direction of motion
vertical upright
worm gears gears in which an axle or shaft has
a screw thread that connects with another gear;
the system changes the speed and direction of
the motion
high gear when the chain on a bicycle passes
around a small back sprocket
m
SCIENCE & TECHNOLOGY 4
GLOSSARY
m
Acknowledgments
The publisher wishes to thank the following sources for photographs, illustrations, articles, and other
materials used in this book Care has been taken to determine and locate ownership of copyrighted material
used in this text. We will gladly receive information enabling us to rectify any errors or omissions in credits.
Photography
p. 1 (centre) Corbis/Richard Fukuhara, p. 1 (bottom) Chris Malazdrewicz/Valan Photos, p. 4 Corbis/Yann
Arthus-Bertrand, p. 5 Ray Boudreau, p. 6 Ray Boudreau, p. 7 Ray Boudreau, p. 8 Ray Boudreau, p. 9 Ray
Boudreau, p. 10 PhotoDisc, Inc., p. 11 Ray Boudreau, p. 12 Ray Boudreau, p. 16 Arthur Strange/Valan Photos,
p. 18 Ray Boudreau, p. 19 Ray Boudreau, p. 20 (left) Jeff Greenberg/Visuals Unlimited, p. 20 (right) Deneve
Feigh Bunde/Visuals Unlimited, p. 21 Ray Boudreau, p. 22 Ray Boudreau, p. 23 Alan Marsh/First Light, p. 25
(top) CP Picture Archive, p. 25 (centre) Ray Boudreau, p. 25 (bottom) Ray Boudreau, p. 26 R. D.
Stevens/Valan Photos, p. 27 Corbis/Warren Morgan, p. 28 Ray Boudreau, p. 29 Ray Boudreau, p. 30 PhotoDisc,
Inc., p. 32 Corbis/Gianni Dagli Orti, p. 33 (top and right) National Museum of Science' Technology, p. 33
(bottom) Corbis/Sean Sexton Collection, p. 34 (left) National Museum of Science & Technology, p. 34 (right)
© 1998 Hiroyuki Kaijo/Rocky Mountain Bicycles, p. 35 (top) Corbis/Phil Schermeister, p. 35 (bottom)
Courtesy of Para-Cycle, Inc., P.O. Box 1906, Windermere, FL 34786-1906 (www.para-cycle.com), pp. 36-37
PhotoDisc, Inc., p. 37 (top) PhotoDisc, Inc., p. 38 Ray Boudreau
Illustration
Tina Holdcroft: pp. 2-3, p. 37
Dave McKay: pp. 14-15, p. 17, pp. 23-26, p. 41
Albert Molnar: p. 13, p. 31, p. 39
Cover Photograph
PhotoDisc, Inc.