Which term describes the moment arm?

• A. The distance between the resistance and the fulcrum
• B. The perpendicular distance between the resistance force and the fulcrum
• C. The distance from the fulcrum to the line of action of the applied force
• D. The distance between the applied force and the fulcrum

Answer: (B)

Moment arm is the perpendicular distance from the pivot to the line along which the force acts. This distance determines how much torque a given force can produce: torque equals force times that perpendicular distance. In a lever with a resistance force, the moment arm is the shortest distance from the fulcrum to the resistance force’s line of action, which is why the description focusing on that perpendicular distance best captures the concept. Simple straight-line distances along the lever or distances to the force’s point of application don’t account for the angle of the force and don’t define the effective lever for rotation.