The Lever Paradox
Put the Lever Paradox on your desk and your students or colleagues will continually puzzle over how it works. If they want a hint, ask them to think about why longer levers generate more force.
The two black 3-hole pins were added to prevent objects from falling off the end. Instead, the black 7-hole beam should have been mounted on top, which would have eliminated the need for the two 3-hole black pins.