Electric motors are devices that convert electrical energy into mechanical energy (electricity into motion). Everyday we are surrounded by electric motors. In cars, for example, there are dozens of electric motors — rolling up the windows, wiping the windshield, adjusting the seats and side-view mirrors, starting the engine when the key is turned, and even a motor connected in reverse to recharge the battery when the car is moving. There are electric motors in your washing machine, refrigerator, blender, can-opener, computer, and all over your home, and they all work on the same basic principle.

If you have ever played with magnets, then you have felt the force associated with magnetic fields. This force is always working to align the fields of the two magnets. A magnet wants to align its south pole (S) with the north pole (N) of another magnet. This is like the famous saying, "opposites attract." Harnessing this magnetic force is how we make motors work.

The motor in this activity consists of three parts: a ceramic magnet, a solenoid electromagnet (a coil of wire) and a battery. When there is current in the wire coil, it produces a magnetic field. One face of the coil becomes a north pole, and the other becomes a south pole. The ceramic magnet attracts its opposite pole on the coil and repels its like pole, causing the coil to rotate. The commutator and brushes of a typical motor are not required for this motor. Instead, half of the insulation is removed on one end of the wire. This means that for half of each spin there is no current in the wire. Therefore, the electromagnet cannot produce a magnetic field for that half spin. As the pole of the electromagnet comes closest to the permanent magnet, the insulated part of the wire turns off the electric current. However, the inertia of the rotating coil carries it through half of a turn, past the insulation. When the uninsulated part of the wire makes contact again, there is an electric current through the coil again. This produces a magnetic field that is in the same direction as when the coil was previously in the same orientation. Therefore, the twisting force on the coil is in the same direction as it was before and the coil rotates in the same direction. That is why this motor requires a push to get started, unlike a typical motor.

• Gather materials and make copies of the Student Instructions Handout, one per group.
• Cut one, two-foot (.6 m) piece of magnet wire for each team.

1. Divide the class into teams of two students each.
2. Conduct the pre-activity assessment activities, as described in the Assessment section.

Figure 1. Magnet wire coil. click for copyright

3. Start about 1.5 in (38 mm) from the end of the wire and wrap it seven times around the short side of a rectangular magnet. Gently slide out the magnet, careful to not alter the rectangular shape of the wire. Leaving a 1.5 in (38 mm) tail opposite the original starting point, cut the wire with wire cutters or needle-nose pliers. Carefully wrap each of the two tails around the coil (closest to that end) so that the coil is securely bound together, and the two tails extend perpendicular to the coil. Your coil should look similar to Figure 1. Note: Be sure that the tails are opposite each other on the coil.

Figure 2. Enlarged cross section (or side view) of wire. click for copyright

4. On one tail, use sandpaper to remove the insulation completely from the end of the tail up to ¼ in (6 mm) from the point at which the tail meets the coil. This tail should look like the left tail in the wire cross section in Figure 2. On the other tail - again leaving a ¼ in (6 mm) section of wire at the point of connection with the coil - lay the coil flat and carefully sand off the insulation from the top half of the wire. This tail should look like the right tail shown in Figure 2.

Figure 3. The bent paperclips. click for copyright

6. Bend the two paper clips to look like those in Figure 3. Use needle-nosed pliers if necessary.
7. To ensure good contact at the battery terminals, sand the paper clips lightly on the surfaces that will touch the battery and the surfaces that the coil will rest on.
8. Use a rubber band to secure the large loop ends of each paper clip to the terminals of the D-cell battery. The battery, rubber band and paper clips device should look like Figure 4.

Figure 4. Use a rubber band to secure the paperclips to the battery. click for copyright

Figure 5. Battery end view, with ceramic magnet in place. click for copyright

8. Place a ceramic magnet on the side of the battery (it will "stick" to the battery) as shown in Figures 5.

Figure 6. The complete motor setup. click for copyright

9. Place the coiled wire with tails into the small loops formed by the unattached ends of the paper clips ("cradles"). Your motor should look like the one in Figure 6.
10. Turn the coil slowly by hand (only touch the insulated part of the wire) and observe the magnetic attraction and repulsion between the electromagnet and the ceramic magnet.
11. (Optional) Remove the magnet from the battery. Use a compass to determine the orientation of the magnetic field of the coil. Remove the coil and replace it on the paper clips in the opposite direction. Use the compass to determine the orientation of magnetic field of the coil again.

1. Position the motor on the edge of a table or countertop (see Figure 6).
2. Bend the end of the wire that has the insulation completely removed into a very small, tight loop.
3. Tie one end of a one-foot (.3 m) long piece of thread around this loop. Tie the other end around a small paper clip.
4. Give the coil a little push to get it to start winding up the string. Once the extra loop and string are added, it may throw the motor off balance. Getting the motor to wrap the string correctly takes a significant bit of tweaking, but it will work. Use your finger as a guide.
5. Once the motor picks up one paper clip, unwind it and try connecting a second paper clip to the first. Keep adding paper clips and trying again until the motor is no longer able to lift the load. We were able to lift 16 paper clips with just this motor, so it is possible!

Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Tally the votes and write the totals on the board. Give the right answer.

• True or False: Like magnetic poles attract and unlike magnetic poles repel. (Answer: False The opposite is true.)
• True or False: A moving magnet can create an electric current. (Answer: True)
• True or False: Engineers design motors, and work to make motors work better. (Answer: True)
• True or False: An electric current does not create a magnetic field (Answer: False, an electric current does generate a magnetic field.)

Question/Answer: Ask students the following questions as they work on the activity.

• What is making the coil spin? (Answer: The magnetic field of the electromagnet [the coil] is interacting with the magnetic field of the ceramic magnet, rotating the coil.)
• Which part of the motor is the electromagnet? (Answer: The coil.)

Figure Drawing: Ask the students to draw a picture their motor, and then have them draw arrows to show how the energy flowed through their motor. (Answer: Starting at the battery, moving through the paper clips, into the coil.)

Engineering Discussion Question: Solicit, integrate and summarize student responses.

• Engineers design many things using electromagnets and motors. What are some examples of items engineers have designed that have motors? (Possible answers: Fan, blender, washing machine, dryer, CD player, electronic toys that move, etc.)
• Which of these (appliances/equipment/devices) might require the most powerful motor? Why? (Answer: Any machine that has to move a heavy load, such as a washing machine, requires a more powerful motor than machines that move small loads, such as an electric can opener. Accept reasonable answers.)
• What parts of the motor should engineers change to build more powerful motors? (Answer: The electromagnet, since the engineers can change the amount of electrical current in an electromagnet as well as the number of coils. The permanent magnet does not have those options for changing.)
• If you were an engineer who was deigning a motor for a new electronic toy, what things would you consider in designing your motor? (Possible answers: How much the motor needs to turn, how big the motor should be, how much work the motor needs to perform, etc.)