Final answer:
The law of conservation of linear momentum states the total momentum of a closed system remains constant without external forces. It's derived from Newton's third law and applies to collisions at macroscopic and atomic levels.
Step-by-step explanation:
The law of conservation of linear momentum states that the total momentum of a closed system remains constant if no external forces act on it. This principle is derived from Newton's third law of motion, which asserts that for every action, there is an equal and opposite reaction. The conservation of momentum is particularly useful for understanding and predicting the outcomes of collisions and other interactions.
Examples of Conservation of Momentum
For example, in an elastic collision between two pool balls, the total momentum before and after the collision is the same. Similarly, in an inelastic collision where two cars collide and stick together, the combined momentum after the collision matches the total initial momentum of both cars separately.
Conservation of Momentum at a Quantum Level
At the atomic and subatomic levels, the conservation of momentum is also upheld. Despite the complex interactions between particles, such as during particle collisions in a collider, the total momentum is conserved before and after the event.