The angular momentum of a body is defined with reference to a chosen point also called the origin. Angular momentum of a body is a cross product given by L = r x p, where r is the position vector of the body about the point chosen as origin and p is the linear momentum of the body. As linear momentum is a cross product of two vectors, it is a vector too and acts in a direction that is given by the right hand rule.

Angular momentum is expressed in the units N*m*s.

The angular momentum of a rotating body has many applications; a gyroscope does not fall over due to its angular momentum, a moving bicycle is stable and does not tip over due to the angular momentum of its wheels.

**angular momentum **is **moment of momentum**, or **rotational momentum** is a conserved vector that states a particular measurable property of an isolated physical system does not change as the system evolves quantity that can be used to describe the overall state of a physical system. The angular momentum **L** of a particle with respect to some point of origin is

where **r** is the particle's position from the origin, **p** = *m***v** *is its linear momentum, and* ×* denotes the cross product*.

The angular momentum of a system of particles (e.g. *a rigid body*) is the sum of angular momenta of the individual particles. For a rigid body rotating around an axis of symmetry (e.g. *the fins of a ceiling fan*), the angular momentum can be expressed as the product of the body's moment of inertia *I* (*a measure of an object's resistance to changes in its rotation rate*) and its angular velocity **ω**:

In this way, angular momentum is sometimes described as the rotational analog of linear momentum.

Angular momentum is conserved in a system where there is no net external **moment of force,**

and its conservation helps explain many diverse phenomena. For example, the increase in rotational speed of a spinning figure skater as the skater's arms are contracted is a consequence of conservation of angular momentum. The very high rotational rates of *neutron star *can also be explained in terms of angular momentum conservation.