In this video, physics teacher Dan Burns explains gravity using a sheet of lycra as the "fabric of spacetime." It's a classic demo, and you can even build your own circular universe on the cheap! (Apparently spandex works well too.)

There's a brief joke in the video referring to the Coriolis Effect. For more on that, see Australian Toilets Don't Flush Backwards Because of the Coriolis Effect.

(Via Kottke.)