Couple in Engineering Mechanics:
A couple is a pair of forces applied to the key of a lock.
Arm of a Couple:
The perpendicular distance (a) between the lines of action of the two equal and opposite parallel forces is known as the Arm of a couple.
Moment of a Couple:
The moment of a couple is the product of the force (i.e, one of the forces of the two equal and opposite parallel forces) and the arm of the couple. Mathematically,
Moment of a couple = P x a
P = Magnitude of the force and
a = Arm of the couple
Classification of Couple:
The couples may be broadly classified into the following two categories, depending upon their direction, in which the couple tends to rotate the body on which it acts:
- Clockwise Couple
- Anticlockwise Couple
A couple whose tendency is to rotate the body, on which it acts in a clockwise direction is known as a clockwise couple. Such a couple is also called a positive couple.
A couple whose tendency is to rotate the body, on which it acts, in an anticlockwise direction is known as an Anticlockwise couple. Such a couple is also called a negative couple.