How and why do objects lose their velocity?

Question

I dont understand how objects lose their velocity when for example they’re in air. Shouldnt the momentum of it be constant?

In: Physics

Answer 1

Conservation of momentum applies to an entire system not to the individual parts. So when a moving object travels through air, some of the momentum is transferred to the air molecules. The total momentum of all the air molecules that the object encounters increases, while the momentum of the object itself decreases.