Tricky Spool Riddle SOLUTION - ft Anne Wojcicki

I'd say that the considerations about where the force is applied is not key. As long as  the distance traveled in any direction is directly proportional to the outer rim length, the circumference of the circle, and the string comes from a smaller circle, the movement will *always* be in the same direction as the the pull on the string, irrespective of angles. Of course, it would take extra tricks to keep any upward movement directly proportional with the rotation of the spool, as it normally slips *very* easily if lifted from the floor. A movement opposite of the pull would require much more string than unwound.