If you have two forces (for instance, a couple of forces) acting on an object and the forces are:
- in opposite directions
- of equal size
- not along the same line of action
...you have got a couple.
Couples produce rotation only. So the object spins faster and faster but it remains on the spot. (In physics speak - no linear acceleration or translation.)
How can we calculate the moment (or torque) of a couple?
So to calculate the moment (or torque) due to a couple you can use:
Moment = Magnitude of one force x perpendicular distance between the lines of action of the forces.
Have a go at this question: