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 Step 2: To find the distance l Net torque = + -----(1) Z 1 2 1 F d1=18.0 x 3.0 1 +24. 0 N m -----(2) 2 F d2=28.0 x (3.0 +l) = - 24. 0 - 8l N m ----(3) 1 Step 3: Net torque Z = +24. 0 + - 24. 0 - 8l Z = 8l-----(4) Since the value has negative sign,...