The law of conservation of momentum states that the total momentum of an isolated system with no external forces is conserved. When physicists say something is conserved they mean that the total amount remains constant. It can neither increase nor decrease.

The surface area of a triangle is proportional to the product of the base and the height. Here the base of each triangle is **r**, the radial distance, and the height is **r·Δθ **(where **Δθ** is the angle that is swept out during the time interval **Δt**)

Dividing the area by the interval of time gives the amount of area that is swept out per unit of time.

In the limit of **Δt** going to infinitisimal the expression for the conserved quantity is proportional to the following expression:

Where **ω** is the angular velocity.

So we have the following conserved quantity: **r**^{2}ω