When they come into contact, ball 1 exerts a contact force on the ball 2, F B1, and the ball 2 exerts a force on ball 1, F B2. We also know that the force will result in a change in momentum:
Definition 1: System
A system is a physical configuration of particles and or objects that we study.
Definition 2: Isolated system
An isolated system is a physical configuration of particles and or objects that we study that doesn’t exchange any matter with its surroundings and is not subject to any force whose source is external to the system. Definition 3: Conservation of Momentum
The total momentum of an isolated system is constant.
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