These spacers are rings with about a 1" inside diameter .. just the right size to fit over a 7/8" magnet :)
So I tried the usual stuff
The Force Field
I tell the kids that I have created a force field .. just like on Star Trek. When the shields are up, the ring will not go over the magnet.
If you hold the magnet, and pull the ring on and off, you can feel the force.
Try, really try, to put a magnet thru the ring .. without touching the ring.
After you give up, use 2 hands and put the ring over the magnet. Now, slowly pull the magnet out from the center of the ring. Remember, aluminum is not attracted to magnets. (I am sure that you were taught that. I certainly was.)
Well, it is already on a string .. so play. If you have been reading these pages in order, then you already know what to do. Move the magnet sideways to make the ring spin (just like for the can on a string). Hold the magnet still, and watch the ring stop spinning.
Creating a gap
Please be careful cutting metal. I have used power saws (a band saw and a scroll saw) to create the gaps. In both cases, I wore eye protection and used a piece of wood to hold the rings. The band saw made a gap that was too easy to see (too wide). On the scroll saw, my extremely fine 4-zero blades would not even scratch the rings .. so I just used a coarser blade. The same blades work in the scroll saw and the jeweler's saw.
Now repeat all the experiments above.