Conservation of Momentum

The concept of conservation of momentum is simple to understand by looking at the Momentum Principle.  The Momentum Principle predicts how much the momentum of a system will change based on external forces, or forces in the surroundings.  Momentum gained by the system is transferred from the surroundings, so we say the momentum is conserved.$$\Delta \vec{p}_{sys} = -\Delta \vec{p}_{surr}$$$$\Delta \vec{p}_{sys} + \Delta \vec{p}_{surr} = \vec{0}$$Basically, all force is equal and opposite.