Description: The conservation of momentum states that the total momentum of a system remains the same before and after an interaction.
Key Terms: Momentum, Newton’s Third Law, initial momentum, final momentum, symmetric system

When momentum, or any quantity in physics, does not change, we say it is conserved. The idea that momentum is conserved when no external force acts is elevated to a central law of mechanics, called the law of conservation of momentum, which states:

In the absence of an external force, the momentum of a system remains unchanged.