Find the turning effect of a force about a pivot.
Torque is the rotational equivalent of force: it measures how effectively a force twists an object about a pivot. It depends on the force applied, the distance from the pivot (the lever arm), and the angle between them: τ = rFsinθ. A force applied perpendicular to the lever arm, at θ = 90°, produces the maximum torque.
The further from the pivot a force acts, the greater the torque, which is why a long spanner loosens a bolt more easily than a short one. A force pointing straight toward or away from the pivot produces no torque at all. Enter the force, lever arm, and angle to find the turning effect in newton-metres.
Torque increases with the lever arm, so a longer spanner produces more turning effect for the same force, making it easier to loosen a tight bolt.
When the force is zero, the lever arm is zero, or the force acts directly along the lever arm (θ = 0° or 180°, so sinθ = 0).