Angular momentum is directed perpendicular to the plane of the rotation, and its magnitude depends on the choice of the origin. The perpendicular vector joining the linear momentum vector of an object to the origin is called the “lever arm.” If the lever arm and linear momentum are collinear, then the magnitude of the angular momentum is zero. Therefore, in this case, the object rotates about the origin such that it lies on the rim of the circumference defined by the lever arm magnitude.

The net torque acting on rotating bodies causes the angular momentum to change, which is a rotational analog for Newton's second law of motion in terms of momentum. It is important to note that this is valid as long as both torque and angular momentum are measured to the same origin, fixed to an inertial frame of reference.

This text is adapted from Openstax, University Physics Volume 1, Section 11.2: Angular Momentum.