Why is momentum conserved in a collision?

After the collision, the momenta of the two separate objects (dropped brick and loaded cart) can be determined from their measured mass and their velocity (often found from a ticker tape analysis). read more

From the Law of Conservation of Momentum, it is known that, in an isolated system, momentum during a collision is conserved. In the case of colliding pucks, there are no external bodies the pucks can transfer their momenta to, since the system is isolated (i.e., the ground isn’t in contact with the pucks, so it cannot receive any momentum). read more

Yet, the total momentum of the two objects (object 1 plus object 2) is the same before the collision as it is after the collision. The total momentum of the system (the collection of two objects) is conserved. A useful analogy for understanding momentum conservation involves a money transaction between two people. read more

One thing that can be confusing for someone learning the concepts for the first time, however, is that although momentum and total energy are conserved in every collision, total energy is only conserved in elastic collisions. read more