Tricky Spool Riddle SOLUTION - ft Anne Wojcicki

That's not the entire answer... let's call pulling force "Fp"; friction force "Ff"; radius of the big wheel "R"; radius of the cilinder "r". We can get 4 cases:

1) Fp*r > Ff*R ----> This means primarily that Fp > Ff and the object will move forward. In this case the torque producted by Fp wins and the spool will rotate clockwise. In a realistic world it would probably be very bouncy. 

2) Fp*r = Ff*R ----> Fp > Ff like before. While the spool will still go forward the torque by Fp will be equal to the Ff one and we will get no rotation.

3) Fp*r < Ff*R ----> two cases:  3a) Fp =< Ff ----> no movements.
                    
                                                      3b) Fp > Ff ----> the spool go forward but the torque producted by Ff will overwhelm the Fp one 
                                                      and it will rotate counterclockwise