Define moment of couple. Write its SI unit.

Moment of a Couple:
The moment of a couple is the rotational effect produced by two equal and opposite forces acting on a body at different points. The forces are parallel but not collinear, meaning they are separated by a certain distance, creating a turning effect (torque) on the object.
Mathematically, the moment of a couple is given by:
Moment of Couple=τ=F×d\text{Moment of Couple} = \tau = F \times d
Where:
• τ\tau is the moment of the couple (or torque),
• FF is the magnitude of one of the forces, and
• dd is the perpendicular distance between the two forces (also known as the arm of the couple).
SI Unit of Moment of Couple:
The SI unit of the moment of a couple is the Newton-meter (N·m). This unit is the same as the unit of torque or moment of force.
Explanation of the Unit:
• A Newton (N) is the unit of force, and
• A meter (m) is the unit of distance. Thus, the unit of the moment of couple, N·m, represents the force applied at a distance from the pivot point, causing rotational motion.
Key Points:
1. The couple produces a rotational effect on an object without changing its translational motion.
2. The moment of a couple is independent of the reference point, which distinguishes it from the moment of force, where the reference point matters.
3. The couple causes pure rotation, not translation, of the object.
In summary, the moment of a couple is a measure of the rotational effect of two equal and opposite forces applied at different points, and its SI unit is Newton-meter (N·m).