What does the principle of conservation of momentum state about a closed system?

The principle of conservation of momentum states that in a closed system, where no external forces are acting, the total momentum remains constant over time. This means that the momentum before any interaction (such as collisions or separations) will equal the momentum after those interactions.

This principle is fundamental in physics because it allows for the prediction of post-event outcomes based on initial states, provided that the system remains closed. In practical terms, this is often observed in collisions, where the combined momentum of colliding objects is conserved, even though they may exchange energy and alter their individual velocities.

The other options do not accurately reflect the conservation principle. The first option suggests that momentum increases with external forces, which contradicts the definition of a closed system. The third option mentions variation based on mass and velocity, but does not address the crucial concept of the system's boundaries and external influences. The last option refers to external forces equating to momentum, which misunderstands the relationship as conservation specifically applies to systems free from such forces.