Momentum: Momentum is the product of an object's mass and velocity. It represents how difficult it is to stop or change the motion of an object.
Conservation of Momentum: This principle states that in a closed system where no external forces act, the total momentum before an event is equal to the total momentum after the event.
Collisions: Collisions occur when two objects interact with each other for a short period of time. They can be classified as elastic (kinetic energy is conserved) or inelastic (kinetic energy is not conserved).