The Snail Tube

One of my favorite purchases at International Puzzle Party was Gary Foshee's "Snail Tube." It falls roughly into the "impossible object" puzzle category, where you have to determine how something was made, or how it works.

Picture a little more than a foot of thick aluminum pipe. It's an empty tube. You hold it straight up and down, and then drop a ball bearing down the tube's shaft (only slightly wider than the ball itself). The metal ball moves at a steady pace through the tube for six and a half seconds. Then it drops out the other end.

It doesn't take long to discover that the ball bearing is a strong magnet. But aluminum isn't magnetic. The ball doesn't stick to the tube's wall; it just saunters down the length of the pipe.

So how does it work?