What is an easy explanation of the Law of Momentum?

Answer 1

An object with mass resists having its velocity changed.

Answer 2

I a mass structure is moving at a certain velocity,it is said that it has motional energy. The final Energy of motion of the moving mass is defined as Ef=MV^2.Where M is the mass value at that velocity ,and V is the velocity of the moving mass.
To define linear momentum we divide the total motional energy by the velocity of the moving mass and we obtain momentum.Hence Linear Momentun is Energy per unit velocity.Its measured in units of kg m/sec.
So Whaterever applies to motion energy also applies to Linear Momentum.
Linear Momentum Refers to a mass that is not at rest.
Whereas a mass at rest only posecesses angular monmentum but not linear momentum.