The Real Simple Motor

The Real Simple Motor

The World's Even More Simple Motor

How it Works …

This simple Homopolar Motor shows how moving charges (an electric current) experience a force when they move through a magnetic field. When the wire is in place, current flows from the battery's positive terminal, through the wire, radially through the magnet, and into the battery's negative terminal.

The direction of the force is perpendicular to both the direction of the current and the direction of the magnetic field, as demonstrated by the Left Hand Rule.

  • The magnetic field is vertical, relative to the table.
  • The current is radially inward at the lower point of contact, toward the center of the battery.
  • The resulting force on the current-carrying wire is tangential. The tangential force, or torque, causes the wire to rotate.

Note that only one connection to the magnet is necessary for the motion to occur. Creating two connections doubles the resulting force, creating a faster spin. Try bending the wire into different shapes, such as a spiral that rests one end on the positive terminal and curls around the battery.


  1. Can I use any size wire? Any copper wire that holds its shape will work, but thicker wire is better for two reasons. First, it his heavier and less likely to flip out of place. Secondly, thicker wire has lower internal resistance and will not get as hot after conducting electricity.

  2. Will ceramic disk magnets work? No. The magnet must be made of a conducting material.

  3. Will it spin faster if I use a bigger battery (or more batteries)? Probably not, but it might last longer.

  4. I've seen other versions without washers. What is the purpose of the washers? Al Gibson (Rochester Adams High School, retired) told us about the washers. The bottom one adds stability, and the top ones keep the wire from sliding off. You can try it without them.

  5. What does Homopolar mean? This motor is homopolar because there is no change of polarity in the wire. The Worlds Simplest Motor ?, by comparison, interrupts the current (and the magnetic field) every half-turn. More efficient motors employ a commutator, which reverses the coil's polarity with every half-turn.

  6. Where can I get the parts? Right here!

Required Equipment

Arbor Scientific Homopolar Motor Kit

January 01, 2008 Collin Wassilak

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