I was goofing off at work today, and I constructed a little device from a push pin (like these: http://en.wikipedia.org/wiki/File:Transparent_pushpins.JPG) and plastic bottle cap (like three of the four of these: http://en.wikipedia.org/wiki/File:Gatorade_G_Series.jpg). What I did is I stuck the push pin into the middle of the bottle cap so that it creates a kind of bowl with a stand. That is, I stuck the pin in the center of the bottle cap so that the “handle” of the pin would be outside and the point would be inside if you put the cap back on the bottle. The device looks a bit like a bird bath, albeit one with a spike in the middle.
Having constructed this device, I then took to spinning it like a top with the push pin on the bottom and the cap on top. And what happens is that if I spin it clockwise, it (obviously) spins like a top clockwise for a while, until it falls over and starts spinning along the rim of the bottle cap with the push pin base more or less in a fixed position. At this point, after a second or two, the device stops spinning clockwise and starts spinning counterclockwise. My question to you is: why does this happen? How does this spinning-top-esque device change directions like that? It just seems odd to me. (Incidentally, the record so far for spinning without hitting the rim is 27 seconds.)