Homopolar Motor
A single AA battery, a magnet and a copper-wire loop spin into the simplest electric motor that actually works.
Start building ↓The build
Stack the magnet
Stick the magnet flat against the battery's negative (flat) end.
Shape the wire
Bend the copper wire into a symmetric loop that balances on the top terminal.
Balance & connect
Rest the wire's dimple on the (+) terminal; let the legs lightly brush the magnet edge.
Watch it spin
Contact completes the circuit and the wire whirls. Tune the legs until it spins freely.
Current flowing through the wire sits inside the magnet's field, so it feels a sideways Lorentz force (F = I L × B) that pushes it in a continuous circle.
A closer look
Because the magnetic field never reverses, there is no commutator or brushes — just one smooth rotation. The wire is essentially a short circuit, which is why it spins fast and gets warm.
Variables to test
- 1 Flip the magnet's poles — which way does it spin now?
- 2 Try a heavier wire loop and time one rotation. How does mass change speed?
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