Simplest motor - screw, magnet, wire and battery.

I've recently presented some fun bits at a Google Event (#GoogleATU), and I had so many requests for more info, that I decided I'll write up my tricks for all to enjoy.

if ((technology == magic) && (magician's code))
  return (void);           // nah, ignore

First up: Homopolar motor. It's not my idea, I have to confess. It was Farraday's idea and he first did this demo in 1821.

What do you need:
1) A battery. Round ones work best. Just take a normal AA battery, one that you won't mind throwing away, as you'll pull a lot of current through it.
Expert tip: For best results, find one where one of the poles on the battery is not perfectly flat. You ideally want it to be a bit rounded or with a slight tip on it to reduce the friction with the screw
2) A screw.
Expert tip: This could be a nail or anything else really, but it needs to a) conduct electricity and b) magnetic field. You want one that is as heavy as your magnet can hold. Too heavy, and it will fall off. Too light, and the friction would be too high. Don't start with pure copper.
A screw with a flat head works best.
3) A round (cylindrical) magnet that conduct electricity. (You can't use one covered in plastic, for example.)
My primary source for these round magnets are the small magnet buttons at the back of some badges... like this one.
4) A piece of wire
Any wire would do, but copper works well, as it does not get attracted by the magnet (much). Don't make the wire too long, it works best if it is short.

Baking instructions:
a) Put the magnet on the screw head.
b) Put the screw sharp tip to one of the battery poles (e.g. +). (This is acting like a low friction ball bearing.)
c) hold the one end of the wire to the other (-) pole of the battery
d) and touch the other end of the wire to the side of the magnet.

As the circuit is completed, current will flow through the circuit, you might see small sparks where the wire touch the magnet, and it should rotate the magnet by 90 degrees very quickly. And the cycle will repeat itself, resulting in a spinning magnet and screw.


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