Lesson Two Sides of One Force

Learning Objectives

After this lesson, students should be able to:

• Describe how a motor works by using an electromagnet and magnetic forces.
• Explain that engineers design electromagnets and motors for use in various applications.
• Relate that hybrid cars use both gasoline and batteries.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Pre-Req Knowledge

An understanding of magnetic forces and what an electromagnet is, as presented in A Magnetic Personality lesson.

Introduction/Motivation

Can you name something with a motor in it? How about something with a magnet? How do these two items relate? Do you know? Well, today we are going to learn about magnets and motors, and how motors work.

Motors work by using electromagnets. Who knows what an electromagnet is? An electromagnet is created by wrapping a coil of wire around a magnetic material, usually iron or steel, and running electricity through it. The electric current makes a magnet out of the material in the middle of the coil. A simple motor is made up of two magnets, an electromagnet and a permanent magnet. We have learned that opposite poles of a magnet attract and like poles repel each other. So, when the two magnets in a motor are next to each other, they either push each other away or attract each other, making the different parts of the motor turn. So, basically, electrical energy from the current in the electromagnet is changed to moving energy (or mechanical energy) in a motor.

Motors can be found in a wide variety of things, from refrigerators and hair dryers, to compact disc players and computers. In fact, any electrical appliance with a moving part likely has a motor. Any of the motors that we use everyday are electromagnetic, and their operation depends on the magnetic field produced by an electrical current. Because motors use around 60% of all the electric power generated in the U.S., many engineers focus on designing motors that run better without using as much electricity.

Have you ever heard a person complain about how much money they have to pay to fill their car with gas? Have you ever noticed a bad smell from a car that is running? What do you think the cars of the future will look like?

The cars of the future may already be here! Car companies have produced hybrid cars, trucks, and SUVs that are powered by both gasoline and batteries. These new cars combine the benefits of gasoline-powered cars and electric cars and put them together. For example, gasoline-powered cars can go fast and travel a long distance between fueling, however they create a lot of bad pollution. They also have low gas mileage and so are expensive to supply with gasoline. Electric cars create almost no pollution, but they cannot go as fast and it is also not easy to find a place to charge your electric car. The combination — hybrid cars — can go faster and farther than electric cars and generate less polluting emissions (bad chemicals and fumes that come from cars) than gasoline-powered cars.

Who do you think designs these neat new cars? That's right, engineers do! Many types of engineers work on the development of hybrid car technology, from mechanical engineers to electrical engineers. Today, we are going to look at how a motor works and how we can use regular batteries to make a motor. Following the lesson students can engage with their own engineering creativity to design electromagnets and motors with the associated activities Creating an Electromagnet and Get Your Motor Running.

Lesson Background and Concepts for Teachers

How do electromagnets work?

Magnets are not the only object that can produce a magnetic field. Electric charge moving in a wire also produces a magnetic field. If we wrap a current-carrying wire in a cylindrical coil, the magnetic field produced resembles that produced by a bar magnet. The coil has a much stronger magnetic field than that of a straight piece of wire. If we put an iron (or nickel, cobalt, etc.) rod through the center of the coil, the rod becomes magnetized, creating an electromagnet (see Figure 1). This electromagnet has a stronger magnetic field than that of a current-carrying coil alone. The strength of the magnetic field can be increased either by increasing the current or by increasing the number of wraps in the coil of the electromagnet.

How is electrical energy converted to energy of motion in a motor?

In a motor, the interaction between two magnets causes a rotating motion. A basic direct current (DC) motor has six parts: the field magnet, armature, commutator, brushes, axle and DC power supply (battery). The armature is an electromagnet. An axle is inserted through the armature at its middle, and the axle is perpendicular to the armature at its midpoint. When there is a current in the electromagnet, it produces a magnetic field. Since we have learned that opposite poles of a magnet attract and like poles repel, the magnetic interactions of repulsion and attraction between the electromagnet and the permanent magnet cause the armature to rotate on the axle.

The commutator is a pair of metal plates attached to the axle that provide the electrical current for the electromagnet. The plates do not completely surround the axle, and this gap between the plates is vital to motor design. Brushes, two pieces of metal or carbon, connect the battery to the electromagnet via the commutator. One brush is connected to the negative terminal on the battery while the other is connected to the positive terminal. As the armature turns on the axle, the direction of current in the electromagnet changes because each half of the commutator contacts alternating brushes. Whenever the current direction in the electromagnet changes, the magnetic field orientation changes. This allows the armature to keep spinning in the same direction on the axle. (Without the commutator and brushes, the armature would rotate at most 180° until the north pole of the electromagnet and south pole of the permanent magnet were together.) The kinetic energy of the rotating axle can be used to do work. For example, the axle of a fan motor is connected to the fan blades.

How are the electric and magnetic forces related?

The electric and magnetic force are really two faces of one phenomenon - electromagnetism. Electromagnetism is responsible for the phenomena of electricity, magnetism and electromagnetic radiation. On one hand, moving charges produce a magnetic field. On the other hand, an electric current can be produced in a circuit by a changing magnetic field. This effect is known as electromagnetic induction and was discovered in 1831 by the experimental chemist/physicist Michael Faraday.

Consider a coil of wire connected to a galvanometer (a device for measuring electric current). If a bar magnet is inserted into the coil, the galvanometer needle deflects only while the magnet is moving. If we hold the magnet still inside the coil there is no longer a current. While we pull the magnet out there is again a current induced in the coil, but in the opposite direction. The electrons in the wire experience a force only when they are exposed to a changing external magnetic field. When the electrons experience this force they move, producing a current.

Associated Activities

• Creating an Electromagnet - Students build an electromagnet and test how modifying its configuration affects the strength of its magnetic field.

  Watch this activity on YouTube

• Get Your Motor Running - Students investigate motors and electromagnets as they construct their own simple electric motors using batteries, magnets, paper clips and wire.

  Watch this activity on YouTube

Lesson Closure

Can you think of any items around your home that have electric motors? (Make a list on the board of the various appliances or equipment named by students.) What role does the motor plays in each device? What makes it turn? If the item is not powered by a battery, then from where does the electricity come? (Possible answers: Electrical outlets, generators.) Could we get a car to run off the same batteries used for radios? (Answer: No, probably not. To run, a car needs more current or electrical energy than a toaster.) What do you think engineers could design to get enough electricity for a car to move? (Possible answers: A plug for the car, a generator, something to charge/store the electricity.) Do you know what types of engineers work on fun projects like making motors work and developing new appliances? Well, mechanical and electrical engineers are the engineers who design motors and all the many everyday conveniences that have motors in them.

I am going to name some more examples of appliances and equipment that have motors. Raise your hand if you have the item in your home, or have seen or used one of them. (Read the following list slowly, allowing students time to raise their hands after each item.) How a bout fans or anything with a fan, such as a computer, air conditioner, hair dryer, microwave oven, refrigerator, humidifier, freezer and refrigerator? How about a clothes dryer, washing machine, dishwasher, blender/mixer/food processor, can opener, garbage disposal, tape answering machine, stereo tape player, computer printer, drill, vacuum cleaner, electric toothbrush, compact disc (CD) player, digital video disc (DVD) player, VCR tape player, electric razor, electric toys that move (radio-controlled vehicles, moving dolls), and garage door opener? Wow! There are so many things that use magnets and have motors in them. Magnets and motors come in all sizes!

Vocabulary/Definitions

armature: The part of an electric motor (or generator) in which a current is generated by a magnetic field, typically consisting of a series of coils surrounding an iron core (i.e., an electromagnet).

battery: A cell that provides electric current.

commutator: A cylindrical arrangement of metal bars connected to the coils of a direct current (DC) motor that provides for a reversal of current into the coils of the motor with every half spin, allowing the motor to spin continuously in one direction.

electromagnet: A fabricated magnet made of a coiled wire wound around an iron core (or any magnetic material such as iron, steel, nickel, cobalt) with electric current flowing through it to produce magnetism. The electric current magnetizes the material.

electromagnetism: Magnetism created by an electric current.

energy: The ability to do work.

engineer: A person who applies her/his understanding of science and mathematics to create things for the benefit of humanity and our planet. This includes the design, manufacture and operation of efficient and economical structures, machines, products, processes and systems.

hybrid: Something that has two or more parts combined together.

magnet: Something that attracts iron and generates a magnetic field.

magnetic field: The portion of space around a magnet where the magnetic forces of the object can be detected.

motor: An electrical device that converts electrical energy into mechanical energy.

permanent magnet: A piece of magnetic material that retains its magnetism after it is removed from a magnetic field.

solenoid: A coil of insulated wire.

work: A force on an object that causes it to move a distance.

Assessment

Pre-Lesson Assessment

Discussion Question: Solicit, integrate and summarize answers from students. Do not worry about giving correct answers at this time. Tell students the answers will be discussed later in the lesson.

• How do you think a motor works?
• What does a battery do?
• How do you think that electricity and magnetism are connected?
• What kind of engineers do you think would work on motors and design cars?

Post-Introduction Assessment

Question/Answer: Ask the students and discuss as a class:

• What is a hybrid car? (Answer: Hybrid gasoline-electric cars have both a gasoline engine and an electric motor.)
• Why is a hybrid car better than a regular car? (Answers: There are several reasons why hybrid gasoline-electric cars are more efficient than gasoline-only cars. The engine in a hybrid car is smaller and more efficient than the engine in a conventional gasoline-only car. Special technologies in hybrid car engines decrease the air pollutants produced compared to conventional car engines. In a hybrid car, the electric motor is used to brake the car, generate electricity, and recharge the batteries. Mechanical engineers design some hybrid cars to be ultra-low weight.)

Post-Lesson Assessment

Flashcards: Each student on a team creates a flashcard with a question on one side and the answer on the other. The questions should be about electromagnetism and how engineers design electromagnets and motors. If the team cannot agree on the answers, they should consult the teacher. Pass the flashcards to the next team. Each member of the team reads a flashcard, and everyone attempts to answer it. If they are right, they can pass on the card to the next team. If they feel they have another correct answer, they should write their answer on the back of the flashcard as an alternative. Once all teams have done all the flashcards, clarify any questions.

One and Done: Ask the students to think of an item that works using a motor, and raise their hands (or indicate thumbs up) when they have an example. (Possible answers: washing machine, dishwasher, can opener, garbage disposal, computer printer, vacuum cleaner, electric toothbrush, compact disc [CD] player, digital video disc [DVD] player, VCR tape player, computer, electric razor, an electric toy [radio-controlled vehicles, moving dolls], etc.). Call on students at random to state their answer (the item with a motor). Students put their hands down once they've contributed an answer. No repeat answers permitted. Remind them that all these items have motors that use magnets to work!

Lesson Extension Activities

Take a class field trip to a junk yard or the back room of an appliance repair shop, looking for motors that students can take apart to see the components that make everyday electromagnet motors. Or, bring into the classroom a broken appliance that can be taken apart to show students the inside motor.

Have students investigate hybrid technology. A vehicle is a "hybrid" when it combines two or more sources of power. Hybrid technology has been around for while. Have students think of other vehicles that use hybrid technology, like mopeds or trains. In addition, ask students to brainstorm other hybrid technologies, like solar- and wind-powered homes, homes heated by natural gas and passive solar heating, etc.

Have students build an "Ultra Simple Electric Generator" using instructions at Amateur Science Hobbyist:http://www.amasci.com/amateur/coilgen.html

Have students build a "Simple Electrostatic Motor" with pop bottles using instructions at Amateur Science Hobbyist: http://www.amasci.com/emotor/emotor.html

Have students investigate other engineering technologies that involve magnets and electromagnets, such as maglev trains.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.