Question

law of conservation of momentum

Answer 1

It says that momentum cannot be created or destroyed. Momentum just passes through systems as opposed to just disappearing in thin air. Momentum can be changed to heat or energy.

Hope this helps :)

Answer 2

What is the Law of Conversation of Momentum?
The law of conservation of momentum states that the total momentum of a closed system does not change. This means that when two objects collide the total momentum of the objects before the collision is the same as the total momentum of the objects after the collision. 
Total momentum meansthe momentum of object 1 plus the momentum of object 2.Object 1 might not have the same momentum before and afterthe collisionbut the amount of momentum object 1 gains from the collisionis the same as the amount of momentum object 2 losesso the total momentum remains the same whether the collision is elastic or inelastic.The total momentum is also the same before and after an explosion.