Final answer:
The law of conservation of momentum states that the total momentum of a closed and isolated system remains constant, regardless of the interactions (like collisions or recoils) that occur within it. This law applies to linear and angular movements, and all internal forces cancel out, leaving the total momentum unchanged.
Step-by-step explanation:
When assessing a closed system, in which there is no gain or loss of mass (closed) and the net force acting on the system is zero (isolated), the law of conservation of momentum is in effect. This physical law states that within such a system, the total momentum of the entire system does not change. This applies to both objects that move in a straight line and that move apart at angles to the original pathway.
Linear momentum is the product of a system's mass and velocity. In a closed system, even if objects within the system interact with each other, such as colliding or recoiling from one another, the internal forces they exert are equal and opposite. As a result, the total momentum before and after any such event remains constant. This principle is upheld in both elastic and inelastic collisions, although in perfectly inelastic collisions, objects stick together and kinetic energy is not conserved.
Point masses, which are structureless particles that cannot rotate or spin, and other objects follow these rules without exception. The momenta of the objects before and after an event (like a collision or explosion within the system) are represented as Pi + Pj = Pi' + Pj', highlighting the conservation of the system's momentum.