A Couple. Two forces equal in magnitude and opposite in direction, acting on an object at two different points, form what is called a couple. Two antiparallel forces with equal magnitudes F1 = F2 = 8.00 N are applied to a rod as shown in ?Fig. E11.21?. (a) What should the distance ?l between the forces be if they are to provide a net torque of 6.40 N ? m about the left end of the rod? (b) Is the sense of this torque clockwise or counterclockwise? (c) Repeat parts (a) and (b) for a pivot at the point on the rod where is applied.

Solution 21E Problem (a) Step 1: Anticlockwise force F = + 100 N Clockwise force F = -2.00 N Net torque = 6.40 N Z Distance from the origin to the point of application of F (d )= 3.0 m 1 1 Distance from the origin to the point of application of F (d )= 32 m2 l