What term describes the tendency of a force to rotate an object about an axis, fulcrum, or pivot?

• A. Moment or torque
• B. Force
• C. Acceleration
• D. Inertia

Answer: (A)

The tendency of a force to rotate an object about an axis, fulcrum, or pivot is called a moment of force, also known as torque. This rotational effect depends on how far the force is from the pivot and the direction of the force relative to that distance. The rotational effect is calculated as torque = r × F, with magnitude equal to rF sin(θ), where r is the distance from the pivot to the point where the force is applied and θ is the angle between the lever arm and the force. When the force is applied perpendicular to the lever arm, the torque is greatest (torque = rF). For example, on an aircraft, applying force farther from the hinge (the lever arm) produces a larger turning moment for a given actuator force, making control surfaces easier to move. If a force acts along a line through the pivot, it produces no rotation because the lever arm is effectively zero. In contrast, force itself is just a push or pull, acceleration is the rate of change of velocity, and inertia is the resistance to changes in motion; none of these specifically describe the rotational tendency about a pivot.