4.3.B—Describe how the selection of a system determines whether the momentum of that system changes

Describe how the selection of a system determines whether the momentum of that system changes.

• Momentum is conserved in all interactions.
• If the net external force on the selected system is zero, the total momentum of the system is constant.
• If the net external force on the selected system is nonzero, momentum is transferred between the system and the environment. 84 Linear Momentum UNIT 4 TOPIC 4.4 Elastic and Inelastic Collisions