In physics, a torque (?) is a vector that measures the tendency of a force to rotate an object about some axis . The magnitude of a torque is defined as force times its lever arm . Just as a force is a push or a pull, a torque can be thought of as a twist. The SI unit for torque is newton meters (N m). In U.S. customary units, it is measured in foot pounds (ft lbf) (also known as 'pounds feet'). Mathematically, the torque on a particle (which has the position r in some reference frame) can be defined as the cross product: ? = r x F where r is the particle's position vector relative to the fulcrum F is the force acting on the particles, or, more generally, torque can be defined as the rate of change of angular momentum, ? = dL/dt where L is the angular momentum vector t stands for time.