In the torque equation T = F x D, what does D represent?

• A. Distance
• B. Diameter
• C. Displacement
• D. Duty

Answer: (A)

Torque gauges how effectively a force can cause rotation, and it depends on how far from the pivot the force is applied. In the formula T = F × D, D is the lever arm—the perpendicular distance from the axis of rotation to the line of action of the force. This distance sets how much rotational effect you get: doubling the distance while keeping the force the same doubles the torque. If the force isn’t perpendicular to the lever arm, use T = F × D × sin(theta), where theta is the angle between the force and the lever arm; the torque is maximal when the force is applied perpendicular to the lever arm. For a perpendicular setup, D is simply the distance from the axis to where the force is applied. The other terms—diameter, displacement, and duty—don’t represent this lever-arm distance in the torque equation.