Final answer:
The law of conservation of momentum states that in an isolated system, the total momentum remains constant before and after a collision, provided there is no net external force.
Step-by-step explanation:
The law of conservation of momentum states that for an isolated system, the total momentum is conserved before and after a collision. This principle is a cornerstone in physics and holds true from the scales of galactic clusters down to subatomic particles. The law is based on the premise that in the absence of external force, the total momentum of a system remains unchanged. It is important to distinguish that momentum is a conserved quantity in a system where the net external force equals zero. Momentum is the product of an object's mass and velocity, showing the impact that object can have upon collision. Moreover, conservation of momentum is a fundamental tool for analyzing collisions and plays a crucial role in understanding subatomic structures via collision analysis in modern physics.
It's noteworthy that the law of conservation of momentum applies universally across physics. Whether you're considering a comet striking Earth or the interactions within a gas containing numerous atoms and molecules, the principle holds so long as no external forces act on the system. If momentum appears to be not conserved, a larger system can be considered which includes the source of the external force, thereby restoring the conservation.