the law of conservation of momentum applies to what type of system?

The law of conservation of momentum applies to a closed (isolated) system in which no net external force acts and the total mass remains constant.

Core idea

• In such a system, the total momentum before an interaction (like a collision or explosion) is equal to the total momentum after the interaction.

• “Closed” or “isolated” means:
  • No net external force on the system.

* No mass entering or leaving the system (mass is constant).

Quick examples

• Two ice skaters pushing off each other on frictionless ice can be treated as a closed system for the short time of the push, so their total momentum is conserved.

• In many collision problems in physics (cars on a frictionless track, billiard balls on a smooth table), the objects involved are taken as an isolated system so momentum conservation can be applied.

In summary, the law of conservation of momentum is valid only for an isolated/closed system with no net external force and constant total mass.

TL;DR: The law of conservation of momentum applies to an isolated (closed) system with no external forces and constant mass.

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