1. The problem statement, all variables and given/known data Quote from the question source: 2. Relevant equations None given, but maybe: Torque = lever arm x force 3. The attempt at a solution I drew a diagram which you can see here: http://i.minus.com/ibzw9bF4vAnaJ.png (The weight differences are probably very exaggerated.) But I am not sure of the answer: I thought that the scale stopped because the lever arm decreases as the scale becomes more vertical, but that happens to both sides so both torques decrease at the same rate (right?). So why do scales stop when slightly unbalanced? It seems like friction is not the answer, because sometimes the scales tip backwards and then forwards until it stops.