Saw a video of this on Youtube, and knew that I had to do the experiment with my boys (8 and 11):
It’s called a homopolar motor, and you can make one with just a AA battery, one or more neodymium magnets, and a loop of solid copper wire. Simple and fun.
The first bit of the video is the wire loop made by my youngest, based on a template I drew up in Inkscape and printed out. Made it a lot easier to get an even loop. The second part is a spiral I made…doesn’t spin quite as smoothly, but it’s a cool visual.
More details at the video link.