3.11.Isolated (closed) system. Momentum conservation law

The law of conservation of momentum is a consequence of the second and third laws of Newton. It takes place in an isolated (closed) system of bodies.

Such a system is called a mechanical system, with no external forces acting on each of its bodies. In an isolated system, internal forces appear, i.e. interaction forces between the bodies included in the system.

Since there are no external forces in a closed system,

or

(3.13)

This equality expresses the law of conservation of momentum, according to which the total momentum vector of a closed system of bodies does not change over time.

Because , then for any processes occurring in a closed system, the speed of its center of inertia remains unchanged.