**conservation laws**

A law that states that, in a closed system, the whole quantity of something will not enhance or reduce, but exactly remain the same; i.e., its rate of alteration is zero. For physical quantities, it states that something can neither be created nor destroyed. Mathematically specking, if a scalar X is the quantity assumed, then

dX/dt = 0,

or, equivalently,

X = constant.

For a vector field F, the conservation law is written as following

div F = 0;

that is, the vector field F refer to divergence-free everywhere (that has no sources or sinks).

Some particular examples of conservation laws are following:

**conservation of mass-energy **

The overall mass-energy of closed system remains constant.

**conservation of electric charge **

The overall electric charge of any closed system remains constant.

**Conservation of linear momentum **

The overall linear momentum of any closed system remains constant.