1)Newton's Second law of motion :- The rate of change of momentum is directly proportional to the force applied on the system.Force applied is directly proportional to the product of mass and acceleration .Let be the initial and final momentums respectively.According to newton's second law :-pf - pi / t ∝ FWe know that,Momentum ( P) = mv .Let v be the final and u be the initial velocity .Now,mv - mu / t ∝ FF ∝ m ( v-u) /tF ∝ ma.F = kma.Here, K is the proportionality constant. It's value is 1 .Units of Force are given by the units of mass and acceleration. Units of force is Kgm/s² .In accordance to honour the contributions of Newton, 1 kgm/s² is termed as 1 Newton.

Momentum = mass * velocity.

Total momentum of a system is always conserved. During a collision, momentum lost by one body is gained by another body. During a collision , assume F1 and F 2 be the forces acting on the two bodies. Assuming that only one collision takes place and assuming it to be an isolated system , F1= -F2 (Newtons 3rd law).

But the collision time is the same for both the bodies, t1 = t2.

Impulse of body 1 = F1*t1 and body 2 = F2*t2

F1*t1 = F1*t2 = -F2*t2 ,

Impulse = F * t , thus Impulse 1 = - Impulse 2

Impulse = change in momentum (by second law of Newton) , thus , m1 * v1 = - m2 * v2 , thus this implies momentum gained by one body = momentum lost by another body.