Vector representation of position, velocity, and acceleration.
What it shows:
A circular train track1 is mounted on a board. X-Y axes are painted on the board with the origin at the center of the circle. Vector Arrows (Newtonian Mechanics, Vectors and Forces in Equilibrium) representing position, velocity, or acceleration may be attached to the train to demonstrate their orientations relative to the coordinate axes as the train chugs around in uniform circular motion. As above, this is nothing more than a cute prop to help visualize rotating vectors.
1 Ours is a Lionel™ train (from Eric Fuchs Inc., Boston); the track is 68 cm (27 in) in diameter. A smaller gauge train would not be very visible to a large audience. To power the train, we are using an ancient W.M. Welch Scientific Co. AC/DC power supply, but any low voltage DC supply (rated ~ 6 V, 5A) will do.