Make your own electric motor

This activity is part of our Science Lab series. Check out the ANU Science Lab for more experiments! In this activity, you will construct a simple homopolar motor using four basic household items to explore electromagnetism, Lorentz force, and electric currents. Watch the video above to see how it is done.

Electric motor materials & ingredients

For this activity:

• 1 AA battery (1.5V)
• 1 iron nail or screw
• 1 small neodymium disc magnet
• 1 piece of copper wire
• Small piece of tape or paper flag (optional, to easily see the spinning motion)

How to make a simple electric motor: Step-by-step instructions

Step 1: Assemble the spinning core

1. Attach the neodymium disc magnet directly to the flat head of the iron nail. Because both are ferromagnetic, the magnet will cling tightly to the nail.
2. Stick a small piece of tape or a folded paper flag onto the point of the nail so you can clearly watch it spin.

Step 2: Suspend the motor

1. Hold the AA battery vertically in one hand with the positive terminal (+) pointing upward.
2. Hang the sharp point of the nail from the bottom negative terminal (-) of the battery. The magnetic force from the neodymium magnet holds the nail suspended in mid-air from the battery terminal.

Step 3: Complete the electrical circuit

1. Hold one exposed end of your copper wire firmly against the top positive terminal (+) of the battery.
2. Gently touch the other exposed end of the wire against the side of the neodymium magnet at the bottom.
3. Watch the nail, magnet, and flag immediately start spinning at high speed!

Image

How a homopolar motor works: The science explained

This simple device is called a homopolar motor, a design first invented by Michael Faraday in 1821. It operates through the interplay of electricity and magnetism:

• Circuit Completion: Touching the wire to the magnet completes an electrical circuit, allowing electric current to flow from the battery, down through the nail and magnet, and back through the wire.
• Lorentz Force: When an electric current moves through a magnetic field, it experiences a physical pushing force known as the Lorentz force.
• Direction: The direction of this force depends on the direction of both the electric current and the magnetic field lines. Because the magnetic field curves outward from the magnet while current flows straight down, the Lorentz force pushes tangentially against the edge of the magnet.
• Continuous Rotation: One side of the magnet is pushed inward while the opposite side is pushed outward, causing the suspended nail and magnet assembly to spin rapidly. Flipping the battery upside down reverses the direction of the current, making the motor spin in the opposite direction.

Science fair projects & taking it further: Experimenting with variables

• Flipping polarity: Flip the battery or turn the magnet upside down. How does changing the current direction or magnetic poles alter the spinning direction?
• Spinning wire design: Skip the nail entirely! Bend the copper wire into a heart or spiral frame resting on top of the battery positive terminal, touching the magnet at the bottom. Can you make the wire frame spin around the battery instead?
• Magnet strength: Compare a standard ceramic magnet against a strong neodymium magnet to measure how magnetic field strength affects rotation speed.