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How to make simple homopolar motor ‘race cars’

Lay out a ‘race track’ of tinfoil, attach two round neodymium magnets to the ends of an AA battery x2 (or more) — the polarity of the magnets matters, so experiment to see how your vehicle behaves (or doesn’t) — then race the little vehicles down the track! If you have two different sizes of magnet on each end of the battery, they’ll do donuts, as shown in the Magnetic Games video above.

These little race cars are simple homopolar motors. From wikipedia:

The homopolar motor is driven by the Lorentz force. A conductor with a current flowing through it when placed in a magnetic field which is perpendicular to the current feels a force in the direction perpendicular to both the magnetic field and the current. This force provides a torque around the axis of rotation. Because the axis of rotation is parallel to the magnetic field, and the opposing magnetic fields do not change polarity, no commutation is required for the conductor to keep turning.

Homopolar motors make for fun experiments. Please note these neodymium magnet hazards to help practice safe & smart science. This video demonstrates a basic homopolar motor using an AA battery, neodymium magnets, and a variety of copper wire shapes:

What other ways can you shape the copper wire? Try this next: How to make the world’s simplest electric toy train, and don’t miss Electromagnetic Induction.

h/t Kottke.

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