torque

In physics, a torque ($\tau$) 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: $τ = r x F$ 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: $τ = dL/dt$ where, L is the angular momentum vector t stands for time.