Definition of a Force Couple

Steps:

• Recall that a couple is a pair of forces that produce rotation without translation.
• Note the forces must be equal in magnitude to ensure no net force.
• Confirm they act in opposite directions on parallel lines, separated by a distance.
• Match properties to options: equal magnitude fits option C.

Why C is correct:

• By definition, a couple requires two forces of equal magnitude acting in opposite directions to create pure torque, as per τ = F × d, where net force is zero.

Why the others are wrong:

• A: Couples act in opposite directions, not the same.
• B: Directions are parallel and opposite, not perpendicular.
• D: Forces act on different lines to produce moment arm, not through the same point.

Final answer: C