# Momentum and Collisions - Mission MC5 Detailed Help

 Which of these collisions demonstrate momentum conservation?
 The law of momentum conservation is all about comparing the total momentum of the system before the collision to the total momentum of the system after the collision. The total momentum of the system is the sum of both objects' momentum. In the diagram, the individual momentum values are listed. If you add these two values together before the collision and do the same after the collision, then you will be able to tell if the total amount is conserved. (See Know the Law - The Law of Momentum Conservation section.)   Be careful though! Momentum is a vector and when vectors are added, direction matters. A momentum vector directed leftward will have to be considered negative when added to the momentum value of a rightward moving object. (See Know the Law - Momentum as a Vector section.)
 The Law of Momentum Conservation: If a collision occurs between object 1 and object 2 in an isolated system, then the momentum change of object 1 is equal in magnitude and opposite in direction to the momentum change of object 2. In equation form m1 • ∆v1 = - m2 • ∆v2   The total momentum of the system before the collision (p1 + p2) is the same as the total momentum of the system of two objects after the collision (p1' + p2'). That is   p1 + p2 = p1' + p2' Total system momentum is said to be conserved for any collision occurring in an isolated system.
 Momentum as a Vector: Momentum is a vector and it has a direction. The direction of an object's momentum is in the same direction that the object is moving.