Spinning Pipe Effect

At the Exploratorium in December, 1996, Tom Tompkins showed me an interesting effect. A piece of PVC pipe a few inches long has an "X" written near one end and an "O" near the other. When the pipe is stationary, both the X and the O are visible at the same time because they are located on the same side of the pipe. When the pipe is spun on the table, however, either the X can be seen or the O can be seen, but not both during the same spin.

	Directions: Cut off a piece of pipe about 3 or 4 inches long. Write an "X" near one end and an "O" near the other with a black magic marker. On a smooth, hard surface, start the pipe spinning by pressing down near one end so that the pipe flies forward as your finger snaps down on the table. Note that if the X is visible then the O isn't and vice verse. Can you figure out why?

If you need some help figuring out how this works, press HERE

Also, check out the Exploratorium page on this topic.