The conservation of linear momentum is a fundamental principle in physics stating that the total linear momentum of an isolated system remains constant if no external forces act on it.
Linear momentum is defined as the product of an object’s mass and its velocity. In a system of interacting objects—like colliding balls or particles—momentum can be transferred between objects, but the overall momentum of the system stays the same, as long as:
- The system is isolated (no net external forces),
- Only internal forces (like mutual pushes or pulls) are present.
This principle explains many phenomena, such as:
- Collisions: In a closed system, the total momentum before and after a collision remains the same, whether the collision is elastic or inelastic.
- Rocket propulsion: A rocket moves forward by ejecting fuel backward—momentum is conserved between the rocket and expelled gases.
- Recoil: When a gun is fired, the forward momentum of the bullet is balanced by the backward momentum of the gun.
In short, conservation of momentum ensures that motion isn’t lost or gained—just redistributed—unless influenced by external forces. It’s a cornerstone of both classical and modern physics.