Momentum is a physical quantity representing the product of an object's mass and its velocity. As a vector quantity, it measures the momentum of motion and is crucial for understanding how forces affect objects in motion. The principle of conservation of momentum dictates that in a closed system—one subject to no external forces—the total momentum of all components within that system remains constant, even if the individual objects interact or collide. This law is fundamental to analyzing interactions across various fields, including celestial mechanics and classical dynamics.