# Momentum and Collisions - Mission MC4 Detailed Help TRUE      or       FALSE: Momentum is always conserved by the two colliding objects in any collision. (Note: Exact wording of question is randomly generated and may vary from the above wording.) The Law of Momentum Conservation: If a collision occurs between object 1 and object 2 in an isolated system (see definition in the Define Help section), 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. Isolated System and External Forces: A system of two colliding objects is considered to be an isolated system if the only momentum-changing forces exerted during the collision are the forces between the two objects themselves. If a third object exerts a force capable of changing one or both of the object's momentum during the collision, then this is considered an external force and the system is not isolated. Whether or not the momentum of a system is conserved is dependent upon whether that system can be considered isolated. So momentum conservation is conditional, not absolute. Conservation of momentum depends on the important condition that the two objects (or three or four) under consideration are part of an isolated system, free from external forces. If one does not know if this condition is met, then one cannot be conclusive about the conserving of momentum by the system.  