In projectile motion with negligible air resistance, momentum is conserved:

1. Momentum can be conserved in different ways along each independent dimension. 2. During projectile motion where air resistance is negligible, momentum is conserved in the horizontal direction because horizontal forces are zero. 3. The horizontal momentum is therefore unchanged throughout the flight. 4. The vertical component of the momentum is not conserved, because the net vertical force is not zero. _Source: OpenStax College Physics for AP(R) Courses 2e (CC BY 4.0), Ch 8 'Linear Momentum and Collisions', sections 8.1-8.7_