The Harvard physics problems of the week are a great set too: <a href="https://www.physics.harvard.edu/academics/undergrad/problems" rel="nofollow">https://www.physics.harvard.edu/academics/undergrad/problems</a>
Reminded me of TIM[1] mechanic puzzles series for DOS. It's incredible how advanced games looked in the beginning of 90s having just a handful of memory.<p>[1] <a href="https://www.dosgamesarchive.com/play/the-incredible-machine/" rel="nofollow">https://www.dosgamesarchive.com/play/the-incredible-machine/</a>
I believe with the first puzzle Leonardo intended the wheel to appear to rotate clockwise. This is why the ball on the right hand side is at the center of the wheel. This is also why there are blocks filling the outer corners but not the inner corners: the balls will fall violently into the outer corners, and roll gently into the inner corners. The "extra" ball is just illustrating the need for blocking the outer corners: the extra ball is shown stuck in such a corner.<p>The drawing wants to lead the viewer into believing that the force of the ball falling to the right and hitting the bottom of the wheel will cause the wheel to turn, lifting all the other balls a small distance. The energy lost from one ball falling a great distance is equal to the energy gained from many balls rising a small distance. This seems to me to be the error the drawing means to invoke.