Moment (torque) is defined as which of the following?

• A. The energy stored by a moving object.
• B. aka torque; force over distance.
• C. The rate of change of velocity.
• D. The net force acting on a body.

Answer: (B)

Moment (torque) is about how a force tends to make something rotate about a pivot. It depends on both the size of the force and how far from the pivot the force is applied, captured by multiplying the force by the lever-arm distance. In vector form, torque is the cross product of the position vector and the force, so its magnitude is τ = rF sin θ, and when the force is perpendicular to the lever arm it becomes τ = rF. This is different from energy (which is stored energy), from acceleration (the rate of change of velocity), and from net force (which drives linear motion). So torque is best described as a force times distance (with the appropriate angle), giving a rotational effect measured in Newton-meters.