What is the principle behind conservation of momentum?

The principle behind conservation of momentum states that the total momentum of a closed system remains constant unless acted upon by external forces.

In more detail, momentum is a vector quantity, meaning it has both magnitude and direction. It is calculated by multiplying an object's mass by its velocity. The principle of conservation of momentum is derived from Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.

In a closed system, where no external forces are acting, the total momentum before an event (like a collision or explosion) is equal to the total momentum after the event. This is because the momentum lost by one object is gained by another. For example, in a game of pool, when the cue ball strikes another ball, it transfers some of its momentum to the other ball. The total momentum of the balls before and after the collision remains the same.

This principle is not only applicable to mechanical systems but also to other fields of physics. For instance, in the realm of quantum mechanics, particles also obey the conservation of momentum. Even in the large-scale universe, galaxies and stars follow this principle during their interactions.

Understanding the conservation of momentum can help us predict the motion of objects after collisions or explosions. It's a fundamental concept in physics that underpins many phenomena in our daily life and the wider universe.