Cracking the SAT Physics Subject Test

Then, by Newton’s second law

If we multiply both sides of this equation by r and notice that rF = τ, we get

Therefore, to form the analog of the law F = ∆p/∆t (force equals the rate-of-change
of linear momentum), we say that torque equals the rate-of-change of angular
momentum, and the angular momentum (denoted by L) of the point mass m is
defined by the equation

L = rmv

If the point mass m does not move in a circular path, we can still define its angular
momentum relative to any reference point.