Couple:

A couple is formed by two unlike parallel forces of the same magnitude but not along the same line.

 

Role of a couple in the steering wheel:

When a driver turns a vehicle, he applies forces that produce torque. This torque turns the steering wheel. These forces act on opposite sides of the steering wheel and are equal in magnitude but opposite in direction. These two forces form a couple.

 

Role of a couple in double arm spanner:

A double arm spanner I used to open a nut. Equal forces each of magnitude F are applied on the ends A and B of a spanner in opposite direction. These forces form a couple that turns the spanner about point O. The torques produced by both the forces of a couple have the same direction. Thus, the total torque produced by the couple will be

 

Total torque of the couple = F × OA × F × OB

                                          = F(OA + OB)

Torque of the couple   = F × AB       …….  (i)

Equation (i) gives the torque produced by a couple of forces F and F separated by distance AB

 

Torque of a couple:

The torque of a couple is given by the product of one of the two forces and the perpendicular distance between them.

 

DO YOU KNOW?

A cyclist pushes the pedals of a bicycle. This forms a couple that acts on the pedals. The pedals cause the toothed wheel to turn to make the rear wheel of the bicycle rotate.