Oh, Ted, I love stuff like that! Thank you! I watched it about 10 times, to figure everything out. I loved my Mouse Trap game I had when I was a kid; same kind of principle. My favorite exhibit in the science museum is this big glass case, taller than I am (just), inside of which several colored balls travel up, down, and around an array of track. It's got an "elevator" operated by a counterweight, a tube that looks like a long sock that some of the balls fall down, and--my favorite--a xylophone; but only every eighth ball "plays" it.
Edit Gravitron--I knew the name would come to me eventually.