Angular momentum is a vector quantity that represents the products of a body’s rotational inertia and rotational velocity. The angular momentum of a system of particles is the sum of angular momenta of individual particles. For rigid bodies, the angular momentum is expressed as the product of the body’s moment of inertia and its angular velocity ω in the following equation:

L=Iω

Angular momentum is conserved only when there is no net external torque acting on the system. An example of angular momentum is a spinning figure skater. The skater will spread out their arms to act against the angular momentum and slow down, or pull their arms in close to their chest to increase angular momentum.

Angular momentum, L, is about a given origin. It is defined as:

L=r x p

Where r is the position vector and p is the linear momentum. Angular momentum is the cross product. Therefore a right hand rule can be used. The right hand rule is where the thumb points in the direction of angular momentum, your hand is the direction of the position vector and your fingers are in the direction of linear momentum.