How to Make the World's Simplest Electric Train

This looks like fun! To make your own electric train, you'll need coiled copper wire, a battery, and 4 strong magnets. Attach the magnets to the end of the battery and place the "train" inside the coiled wire.

The toy train zips along the copper track, which you can arrange in a circle to keep the movement going.

(Video Link)

I'm going to admit my ignorance: I'm not really sure why this works. Some YouTube commenters say that this toy is a homopolar motor, which is a type of electric motor in which the surrounding copper wire completes a circuit.

Commenters, is that correct?

-via Twisted Sifter

Homopolar just means the electricity is not changing direction (i.e. not using AC power nor a commutator to mechanically switch direction of current in the wire). A current in a magnetic field will experience a force perpendicular to the current and magnetic field lines. There will be places in this where the field lines go radially (in and out of the tube) while the current is mostly going around the tube, giving a force in the third direction: along the tube
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