Question

Please tell me rhat what is conservation of momentum

Answer 1

it is newton's law stating that momentum of system is constant unless no external force is acting on that particular system

Answer 2

Conservation of momentum is a fundamental law of physics which states that the momentum of a system is constant if there are no external forces acting on the system. It is embodied in Newton's first law (the law of inertia).

Suppose we have two interacting particles 1 and 2, possibly of different masses. The forces between them are equal and opposite. According to Newton's second law, force is the time rate of change of the momentum, so we conclude that the rate of change of momentum  of particle 1 is equal to minus the rate of change of momentum  of a particle 2,

(1)

Now, if the rate of change is always equal and opposite, it follows that the total change in the momentum of particle 1 is equal and opposite of the total change in the momentum of particle 2. That means that if we sum the two momenta the result is zero.

But the statement that the rate of change of this sum is zero is equivalent to stating that the quantity  is a constant. This sum is called the total momentum of a system, and in general it is the sum of all individuals momenta of each particle in the system.