We found several of these on a walk in Grizedale Forest. Turning forces are given several different names most notably moment and torque. This is a COUPLE. A couple is when two equal but opposite forces, one on either side of the pivot, push the object round. To calculate the size of the couple you do one force x the distance between the forces. Since the individual moments of each force = force x distance from pivot, but the distance between the two forces is twice the distance from each one to the pivot, the formula for a couple is just the sum of the two moments.
