State and explain law of conservation of momentum with example

The law of conservation of momentum states that provided there is no exterior force or in an isolated system the total linear momentum of two colliding bodies remains the same or is conserved

An example is if two bodies collide

in this case, the sum of the two momenta before collision is equal to their sum after collision. What momentum one particle loses, the other gains. So the algebraic sum is equal

grav force prop 1/r squared 2r all squared is 4rsquared 1/4rsquared quartered