Momentum is an especially important quantity in physics because it is:

1. Conserved quantities let you relate a situation before and after without tracking the details. 2. Momentum is an important quantity because it is conserved. 3. Much of what we know about atomic and subatomic particles comes from collision experiments. 4. Momentum is crucial to understanding those particles for exactly that reason. _Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 8 'Linear Momentum and Collisions', sections 8.1-8.7_