Define the law of conservation of momentum.

The law of conservation of momentum states that the total momentum of a closed system remains constant if no external forces act on it.

In more detail, the law of conservation of momentum is a fundamental principle in physics that originates from Newton's third law of motion. This law states that for every action, there is an equal and opposite reaction. In terms of momentum, this means that the momentum before an event must be equal to the momentum after the event, provided no external forces are involved.

Momentum, denoted by the letter 'p', is a vector quantity that is defined as the product of an object's mass and its velocity. In a closed system, the total momentum is the vector sum of the individual momenta of all the objects in the system. If two objects collide, the total momentum before the collision is equal to the total momentum after the collision. This is true for both elastic and inelastic collisions.

The law of conservation of momentum can be applied to various situations in physics, including collisions, explosions, and particle interactions. It is also crucial in the study of fluid dynamics, quantum mechanics, and relativistic mechanics.

For example, consider a game of pool. When the cue ball strikes another ball, the total momentum of the two balls before the collision (the moving cue ball and the stationary target ball) is equal to the total momentum of the two balls after the collision. This is why the balls move away from each other after the collision.

In conclusion, the law of conservation of momentum is a fundamental concept in physics that describes the constant total momentum in a closed system, provided no external forces are acting on it. It is a direct consequence of Newton's third law of motion and is applicable in a wide range of physical phenomena.