Moment of a Couple

• Two forces F and -F having the same magnitude, parallel lines of action, and opposite sense are said to form a couple.
•  Moment of the couple,
  

•  The moment vector of the couple is independent of the choice of the origin of the coordinate axes, i.e., it is a free vector that can be applied at any point with the same effect.
• Two couples will have equal moments if
  

•  the two couples lie in parallel planes, and
• the two couples have the same sense or the tendency to cause rotation in the same direction.