While on the subject of the apparently impossible, here’s another teasing puzzle that woodworkers can make to annoy their friends. It consists of 3 pieces: a cylinder, a symmetrical double cone and an inclined plane.
Surprisingly, placed together like this, there is no movement in either cylinder or cone. Wouldn’t you expect them to roll down the inclined plane?
The cylinder does, of course, roll down the plane but to take the photograph, I’ve used a ruler as a chock to prevent this happening.
The cone, on the other hand, has an inexplicable tendency to roll up hill. Once again, I’ve used a ruler as a chock to prevent it doing so.
These still photographs don’t really convey the anti-gravity properties of the double cone. For a more convincing demonstration, have a look at this video on YouTube.
Or, in case the link doesn’t work, paste this url into your browser: http://www.youtube.com/finelystrung#p/a/u/0/g7dCCskRMUg
Finely Strung 