The product of linear momentum and the distance from the axis is called angular momentum, denoted by L.

L = ∑ m_{i} ω r_{i} r_{i} = (Σ m_{i} r_{i}^{2})ω

**L = Iω**

The angular velocity is the same for all the particles and the term within brackets is the moment of inertia. Like the linear momentum, the angular momentum is also a vector quantity. The unit of angular momentum is kg m^{2} s^{–1}.

The rate of change of ω is α and Iα = τ. Therefore, the rate of change of angular momentum is equal to **torque**.

**dL/dt = τ = I dω/dt = I α**