Under which conditions does the law of conservation of momentum apply?

The law of conservation of momentum states that within an isolated system, the total momentum remains constant if no external forces act on it. This principle applies because in an isolated system, all internal forces can be considered to be balanced, meaning the momentum gained by one object must be equal and opposite to the momentum lost by another object.

Isolated systems are crucial for this law because any external force – such as friction or a push from another object – can change the momentum of the system, making it impossible to rely on the conservation law. This is why the condition of being isolated is fundamental to the principle; it ensures that the influences of external forces are removed, allowing for true momentum conservation. The statement about the applicability of momentum conservation during all types of collisions is also accurate, but only when these collisions occur within isolated systems. Changes in temperature or interactions in non-isolated systems introduce variables that can affect momentum, thus invalidating conservation in those scenarios.