If r is the vector from the reference point to the mass, then the angular momentum is
L = rmv⊥ = rmv sin θwhere v⊥ is the component of the velocity that’s perpendicular to r.
For a rotating object, the angular momentum equals the sum of the angular
momentum of each individual particle. This can be written as
L=Iωwhere I is the object’s moment of inertia and ω is the angular velocity (to be
discussed later). I is basically a measure of how difficult it is to start an object
rotating (analogous to mass in the translational world). I increases with mass and
average radius from the axis of rotation.
Newton’s First Law