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INVESTIGATION
Collaborative Learning
A3
This investigation is Exploros-enabled for tablets. See page xiii for details.
A3 How a Motor Works
Key Question: How does a motor work?
Materials for each group
The electric motor revolutionized human technology.
With an electric motor, power could easily be transferred
via electricity from one place to another. The electric
motor is based on the principles of electricity and
magnetism. In this investigation, students learn about
the parts of an electric motor and construct a working
motor. They learn how permanent magnets and an
electromagnet work together to cause a motor to spin.
They learn that they can control the direction of spin by
changing the orientation of the magnets.
yy F rom the Electric Motor kit: electric motor with
the battery pack, 7-8 permanent magnets,
1 electromagnet, and the orange commutator disk
yy Four D-cell batteries*
*provided by the teacher
Online Resources
Available at curiosityplace.com
yy Equipment Video: Electric Motor
Learning Goals
✔✔Construct a working motor.
✔✔Use an electromagnet and explain how it reverses its
yy Skill and Practice Sheets
yy Whiteboard Resources
yy Animation: Rotor Magnets
north and south poles.
✔✔Determine the direction a motor will spin given the
orientation of its magnets.
yy Student Reading: Electromagnets
Vocabulary
commutator – the device that switches the direction of
electric current in the electromagnet of an electric motor
GETTING STARTED
Time 50 minutes
electric motor – a device that converts electrical energy
into mechanical energy
Setup and Materials
electromagnet – a magnet created by a wire carrying
electric current
1. Make copies of investigation sheets for students.
2.
permanent magnet – a material that retains its
magnetic properties
Watch the equipment video.
3. Have students work in small groups of three to five.
rotor – the rotating disk of an electric motor or generator
4. Review all safety procedures with students.
NGSS Connection This investigation builds conceptual understanding and skills for the following performance expectation.
MS-PS2-3. Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.
Science and Engineering Practices
Asking Questions and Defining Problems
Disciplinary Core Ideas
PS2.B: Types of Interactions
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Crosscutting Concepts
Cause and Effect
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How a Motor Works
BACKGROUND
Electric motors convert electrical energy into
mechanical energy. Permanent magnets and
electromagnets work together to make electric motors.
The secret to making an electric motor work is in the
ability of an electromagnet to reverse its north and
south poles.
In this investigation, students first try to make the rotor
spin by manually flipping permanent magnets near the
rotor magnets. Next, students see how an electromagnet
can be used instead. Just as with the finger magnet, the
electromagnet must switch from north to south as each
rotor magnet passes by to keep the rotor turning.
The device that makes this happen is called a
commutator. As the rotor spins, the commutator,
which is a plastic disk, reverses the direction of the
current in the electromagnet (when the dark and clear
segments of the disk interact with the photogate on
the electromagnet). This reversing of current makes
the electromagnet’s side facing the disk change from
north to south, and then back again. The electromagnet
attracts and repels the magnets in the rotor, and the
motor turns.
The three things you need to make a motor are 1) a
rotating part, called a rotor, with magnets that have
alternating polarity; 2) one or more electromagnets; and
3) a commutator that switches the direction of current
in the electromagnets back and forth in the correct
sequence to keep the rotor spinning.
The three main parts of an
electric motor
1 Rotor
Electromagnet
Current
N
2 Fixed magnets
on a rotor
A commercial electric motor that runs on batteries
doesn’t look quite like the spinning disk motor used in
the investigation. However, the same three mechanisms
are still there. The difference is in the arrangement
of the electromagnets and permanent magnets. This
illustration shows a small battery-powered electric motor
and what it looks like inside with one end of the motor
case removed.
The permanent magnets are on the outside, and they
stay fixed in place. The electromagnets are in the
rotor, and they turn. The rotating part of the motor,
including the electromagnets, is called the armature. The
armature in the illustration has three electromagnets,
corresponding to the three coils.
The wires from each of the three coils attach to three
metal plates (the commutator) at the end of the
armature. As the rotor spins, the three plates come into
contact with positive and negative brushes. Electric
current flows through the brushes into the coils. As the
motor turns, the plates rotate past the brushes, reversing
the positive and negative connections to the coils,
which make the electromagnets’ magnetic poles switch
positions. The turning electromagnets with alternating
poles are thus attracted and repelled by the permanent
magnets, and the motor turns.
Motors that run on AC electricity are easier to make
because the current switches direction all by itself.
Almost all household, industrial, and power tool motors
are AC motors. These motors use electromagnets for
both the rotating and fixed magnets.
3 Commutator
Switches the
direction of
current in the
electromagnet
at the right time
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A3
5E LESSON PLAN
Engage
Explain
Ask students, “When do you think the first electric car was
built?” They may think that current designs of electric and
hybrid cars are a brand new green technology. Explain to
students that the original electric cars were the horseless
carriages of the 1800s. Electric motor technology has been
around for over 200 years!
Revisit the Key Question to give students an opportunity
to reflect on their learning experience and verbalize
understandings about the science concepts explored in
the investigation. Curiosityplace.com resources, including
student readings, videos, animations, and whiteboard
resources, as well as readings from your current science
textbook, are other tools to facilitate student
communication about new ideas.
Animation
Rotor Magnets
Ask students, “Can you name something other than a car
that has a motor?” List answers on the board. From the
variety of answers, point out how many different places in
our lives we use electric motors.
Elaborate
Electric motors transform electrical energy into
mechanical energy. Have students draw all the
transformations of energy that take place in their electric
motors. Then have them think up and draw a type of
work the electric motor could do with the mechanical
energy from the output.
Explore
Have students complete Investigation A3, How a Motor
Works. Students learn about the parts of an electric
motor. In particular, they learn how permanent magnets
and an electromagnet work together to cause a motor
to spin. They learn that they can control the direction of
spin by changing the orientation of the magnets.
Evaluate
yy D
uring the investigation, use the checkpoint
questions as opportunities for ongoing assessment.
yy A
fter completing the investigation, have students
answer the assessment questions on the Evaluate
student sheet to check understanding of the
concepts presented.
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How a Motor Works
Explore
INVESTIGATION
A3
Name ____________________________________________ Date ________________________
A3 How a Motor Works
Materials:
✔ 7-8 ceramic magnets
How does a motor work?
Did you know that magnets are important parts of electric motors? In this
investigation, you will be using permanent magnets and an electromagnet to
build a simple motor and learn how magnets work in a motor. A permanent magnet
is a type of magnet that always has its magnetic properties. An electromagnet is a
device that is magnetic when electricity is flowing through it.

from the Electric
Motor kit
the battery pack,
an electromagnet,
and the orange
commutator disk
Take your electric motor apart and set it up like the picture shows.
1. First, uncover the rotor. Then, take out
all the magnets.
A3
a. Describe how you got the rotor to spin in one direction. What did you have to do with the magnet in your
hand to get the rotor to spin?
I flipped the magnet over each time another magnet passed by. My
magnet attracted the magnets in the rotor.

What is an electromagnet?
Electromagnets are devices that become magnets when electricity flows through
them. An electromagnet is usually made with a coil of wire wrapped around a
steel or iron core. Electricity flows through the coil of wire. This causes the steel
pin to become magnetized with a north and south pole.
One difference between an electromagnet and a permanent magnet is that an
electromagnet can reverse its north and south poles. This is done by changing the direction of the electric
current in the electromagnet. If you know the direction the current flows, you can tell which end of the
electromagnet is the north pole.
2. Now, place six of the magnets in
the rotor so they are evenly spaced.
Alternate the orientation of the north
and south poles as shown in the picture.
The north pole is at the top of the steel pin when the current is
going counter-clockwise around the pin. The north pole is on the
bottom of the pin when the current is going clockwise.
3. Put another magnet in your hand. Bring
it close to the motor so that it repels a
magnet in the rotor. What happens?
I held my magnet so
that the north pole was
pointing toward a magnet
in the rotor with its north
pole facing outwards. The result was that the rotor turned clockwise,
but stopped when the next magnet (with its south pole facing out)
jumped out of the rotor and stuck to the magnet in my hand.
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Can be duplicated for classroom use
INVESTIGATION
4. Try to make the rotor spin by using your magnet to “push and pull” on the rotor magnets. It may take
some time to perfect your technique because the magnets in the rotor easily jump out of the rotor and
stick to the magnet in your hand.
✔ Electric Motor with
✔ 4 D-cell batteries
Looking inside the electric motor
Explore
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A3 How a Motor Works
Electric Motor
Look at the electromagnet that comes with the electric motor.
You will see a coil of copper wire wrapped around a thick steel
pin. The north and south pole of this pin switches when the current going through the electromagnet changes
direction. The electromagnet that comes with the electric motor has a light-beam switch. Blocking the light
beam causes the current to change direction in the coil of wire. The little green lights tell you where the north
pole is located on the electromagnet.
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Can be duplicated for classroom use
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A3 How a Motor Works
Electric Motor
Guiding the INVESTIGATION
Guiding the INVESTIGATION
 Looking inside the electric motor
 What is an electromagnet?
Circulate among the groups, making sure that each
student is an active participant in the investigation.
If students have trouble making the disk spin,
suggest that they hold the magnet slightly above the
rotor magnets and push downward until the rotor
magnet is repelled. Then they must quickly pull the
magnet backward as the rotor spins. Otherwise they
may pull the next magnet right out of the motor.
The secret is to keep reversing the magnet in their
fingers to push and pull each magnet in the rotor
as it passes by. With a little practice, each student
should be able to spin the rotor. Another technique
is to stack two magnets together in your hand for a
stronger magnet.
Turning a motor using magnets is fun and helps
students see how the motor works. But if the only
way to turn a motor was to stand there and flip
magnets all day, it wouldn’t be a great invention.
With an electromagnet, the north and south poles
can be switched with electricity.
Electromagnets involve a connection between
electricity and magnetism. They are a type of magnet
created when there is electric current flowing in a
wire. Electromagnets are a temporary magnet, and
their magnetic field only exists when the electric
current is flowing. Their poles can be reversed, back
and forth between north and south, by reversing the
direction of their current.
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A3
Explore
INVESTIGATION
A3
Explore
1. Take the magnets out of the rotor. Place the orange commutator disk on the rotor and gently secure it
with the nut. The orange disk has three black spaces and three clear spaces around the edge.
A3
INVESTIGATION
3. Slide the electromagnet back in place toward the center of the rotor and gently tighten down the thumbnuts to make electrical contact.
2. Place the electromagnet on the electric motor. Slide it toward the center of the rotor and gently tighten
down the thumb-nuts to hold it in place and make electrical contact.
3. Connect the battery pack with the red wire in the red socket and the black wire in the black socket.
4. Hold down the RUN button and slowly rotate the rotor with your hand.
a. What do you notice about the position of the north and south poles of the electromagnet as you spin the rotor?
The poles of the electromagnet switch positions.
b. When is the north pole of the electromagnet closest to the rotor? When is the south pole of the
electromagnet closest to the rotor?
The north pole is closest to the rotor when a clear section is
under the light beam switch. The south pole is closest to the rotor
when a black section is under light beam switch. This happens
independently of which way the rotor is turning.

4. Hold down the RUN button. The rotor will start spinning! You may need to give the rotor a little push at
first. Now, you have a working electric motor!
Working with the electromagnet

1. Now, take off the orange disk and put the six magnets back in place as shown below. You will need to
loosen the thumbscrews on the electromagnet and slide it back before removing the disk.
Analyzing the motor’s motion
Now, you will analyze the motor’s motion. Hold down the RUN button and slowly turn the rotor by hand.
Watch the green light on the electromagnet as the alternating black and clear sections of the rotor pass under it.
2. Replace the disk on the rotor like the picture shows. Make sure that the boundary lines between the black
and clear sections are positioned at the centers of your six magnets.
a. What do you notice? How do the poles of the electromagnet change compared to the poles of the
permanent magnet in the rotor?
The poles keep switching. When the south pole of a permanent
magnet is close to the electromagnet, the north pole of the
electromagnet is closest to the rotor. The opposite occurs when
the north pole of a permanent magnet in the rotor is close to the
electromagnet.
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Can be duplicated for classroom use
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A3 How a Motor Works
Electric Motor
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Can be duplicated for classroom use
SCIENCE AND LANGUAGE
TEACHING TIP
Commutator – (from Latin mutare meaning “to
If the electric motor doesn’t work properly, try the
following troubleshooting procedures:
Commutator shares its origin with two other
words that should be familiar to students:
mutate and commute. Ask students to think
about what happens when something mutates.
Steer students toward using the word change to
describe mutations. Then ask, “What does it mean
when someone commutes to and from work?” A
commuter travels from home to work and then back
again home. “Commutator” combines meanings
from both of these words. The commutator changes
the direction of current altogether, like a commuter
travels to work and back again, or a mutation
changes something completely.
1. Check the batteries. Is one of the green lights on
when the RUN button is held down? Sometimes
the battery holders are tight and prevent the
batteries from touching in the center. Rolling the
battery around usually works to fix this problem.
change altogether”)
2. Check that the electromagnet is not touching
the rotor. If it is, slide it back a little.
3. Check that the thumb nuts on the
electromagnet are making a good connection
to the circuit board.
4. Check that the commutator disk is lined up so
the edges from clear to black are aligned with
the centers of the four magnets in the motor.
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How a Motor Works
Explore
INVESTIGATION
A3
b. How do you think the electromagnet, the permanent magnets, and the disk work together to make the
rotor spin? Write down your ideas as a short paragraph or as a series of steps.
The poles of the electromagnet switch every time a black/clear
boundary passes the light beam on the electromagnet. The switch
of the pole is such that the next permanent magnet in the rotor is
attracted (or pulled) toward the electromagnet. The orientation of the
magnets relative to the sections indicates whether the rotor will spin
clockwise or counterclockwise. For example: (1) The clear section of
the disk is under the beam and the north pole of the electromagnet
is closest to the rotor; (2) This north pole is attracting the outward
facing south pole of the next permanent magnet in the rotor; (3)
The south pole of this permanent magnet reaches the beam of the
electromagnet at the same time as the boundary from clear to black;
(4) The poles of the electromagnet switch—now the south pole of
the electromagnet is closest to the rotor; and (5) The permanent
magnet under the beam is repelled and the next magnet in the rotor
(with the north pole facing out) is attracted to the electromagnet.
Explore
INVESTIGATION
A3
c. Look at the following pictures and determine where the north pole is when the disk is in each position.
Circle the picture that shows the correct location of the north and south poles for each disk position. Be
sure to use the electric motor to see if your answer is correct.
When the black section is under the electromagnet, the south
pole of the electromagnet is closest to the rotor. The permanent
magnet nearest the electromagnet is being repelled and the next
permanent magnet in the rotor (with the north pole facing out) is
being attracted. When the clear section is under the electromagnet,
the north pole is closest to the rotor. The permanent magnet nearest
the electromagnet is being attracted.
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Can be duplicated for classroom use
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A3 How a Motor Works
Electric Motor
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Can be duplicated for classroom use
A3 How a Motor Works
Electric Motor
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STEM CONNECTION
Hybrid Cars Electric motors are quiet, produce no
emissions, and are able to generate powerful forces
very quickly. Despite these advantages, electric cars
have not been widely accepted in the marketplace.
Their biggest drawback is battery weight: one kilogram
of gasoline yields more than 30 times the energy
stored in one kilogram of batteries. In order to store
enough energy to be practical, electric cars are heavy
and have a range of only 50 to 100 Conventional
miles before the
car
batteries need to be recharged.
Conventional car
Hybrid c
Gas tank
Gas tank
High-powered
engine
Batteries
Hybrid car
Gas tank
Hybrid cars combine the advantages of gasoline and
electrical power. In the most promising hybrids on
the market today, a small, efficient gasoline engine is
combined with a battery-powered
The
Gas tank electric motor.High-powered
engine
two power sources work together to achieve good
performance and excellent fuel efficiency.
Batteries
Small high-efficiency
engine
Electric
motor
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Small h
A3
Explore
INVESTIGATION
A3
d. Suppose you have a rotor with magnets
like the ones in the picture to the right.
The electromagnet has a north pole facing
in towards the rotor. Which way will it
turn? Circle the correct direction.
Evaluate
INVESTIGATION
A3
Name ____________________________________________ Date ________________________
1. What is the difference between a permanent magnet and an electromagnet?
It will spin clockwise.
e. How can you make your motor spin the
other way? Explain your procedure.
The motor will spin the
other way if all of the permanent magnets
(shown in the diagram) are flipped. For example, all the magnets
with the north pole facing out would be flipped to have the south
pole facing out, and all the magnets with the south pole facing out
would be flipped to have the north pole facing out.
The north and south poles in a permanent magnet are fixed and
don’t change positions. The poles for an electromagnet are created
when electricity is flowing. The orientation of the poles depends on
the direction that the current is flowing, so they can be easily
reversed.
2. Electric motors are everywhere. List at least 5 things you own or use that contain electric motors. How
many electric motors have you used today?
Common objects that have motors are: cars, blenders, hair dryers,
food processors, and fans. Today, I have used two objects that have
electric motors—a car and a fan.
3. Would the motor at right spin? Why or why not?
No, the setup would not spin because the permanent
magnets all have their north poles facing outward.
This setup would spin if the orientation of
the magnets alternated.
4. Examine the two motor designs at right. Which one will spin faster?
Explain your answer.
Disk B will spin the fastest because there
are more opportunities for the poles to
switch. Each time the poles of the
electromagnet are switched is an opportunity for the disk to be
pulled around. In these terms, disk B gets “pulled” six times for each
rotation, while disk A gets pulled two times.
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Can be duplicated for classroom use
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A3 How a Motor Works
Electric Motor
Ordinary car engines are built with extra power
capacity to provide rapid acceleration when passing or
starting. Cruising at constant speed requires less than
15 percent of a typical engine’s maximum power. Fuel
efficiency suffers because large engines are inefficient
at the low power levels used for 95 percent of driving.
Conventional engine designs are a compromise
between the high power needed for acceleration and
the low power needed for normal driving.
In a hybrid car, the small, high-performance gasoline
engine is used for normal driving. The electric
motor supplies extra power for fast starts and rapid
acceleration. The gas engine can be relatively powerful
while producing ultra-low levels of emissions. One
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A3 How a Motor Works
Electric Motor
STEM CONNECTION
(continued from previous page) Copyright © CPO Science
Can be duplicated for classroom use
hybrid model has an engine that weighs a mere
124 pounds yet produces 67 horsepower.
Hybrid cars do not need to be “plugged in” overnight
to be recharged like pure electric cars. The gasoline
engine includes an electric generator that continuously
recharges the batteries while you are driving.
One of the most innovative developments in hybrid
technology is regenerative braking. Conventional
braking systems dissipate a car’s kinetic energy
through friction, resulting in heat. In a hybrid car,
however, the electric motor also works as a generator.
Regenerative braking uses some of the car’s kinetic
energy to turn the motor into a generator that charges
the batteries during slowing or stopping. This process
recycles kinetic energy that would otherwise be lost.
Electric Motor
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How a Motor Works
Evaluate
INVESTIGATION
A3
Notes and Reflections
5. Magnetically levitated (also called “maglev”) trains use electromagnets
to lift a train a few inches above the track and to pull it forward.
Research maglev trains and find out where they are in use today.
In an effort to reduce traffic, the U.S.
government is supporting research on the
development of the first maglev train for the
country. Maglev trains are much faster than
traditional rail systems because they travel on air, held off the track
by a magnetic field. By “floating” the train on a powerful magnetic
field, the friction between wheels and rails is eliminated. Maglev
trains achieve high speeds using less power than a normal train.
The first commercially operated maglev train is in China and runs
between the city of Shanghai and the Pudong Airport. The train
travels the 30 km (19 mile) distance in 7 minutes 20 seconds,
reaching a speed of 431 km/h (268 mph).
A3 How a Motor Works
Electric Motor
Copyright © CPO Science
Can be duplicated for classroom use
WRAPPING UP
Have your students reflect on what they
learned from the investigation by answering the
following questions:
1. What are the important parts of an
electric motor?
2. What is an electromagnet?
3. How can you control the direction that a
motor spins?
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