Kinetic Sculpture, George Rhoads (Boston Children's Hospital)

I'm a sucker for these. The one in the Terminal C baggage carousel at the Philly Airport (along with others presumably) has mechanisms that behave out of phase with respect to the rest of the device, and are themselves altered by their interactions with the balls in the sculpture. Watch one of these for very long and you're likely to meditate on questions of determinism, digital vs. analog information, and irrational numbers. Here's Mr. Rhoads's website.