Conservation of momentum

Science

Definition

The law of conservation of momentum states that the total momentum of a closed system remains constant if no external forces act on it. This principle is especially useful in analyzing collisions and explosions.

Examples

  • When a gun fires, the bullet moves forward and the gun recoils backward with equal and opposite momentum
  • In ice skating, when two skaters push off each other, they move apart with momenta that are equal in magnitude but opposite in direction
  • Rocket propulsion works because the momentum of exhaust gases ejected backward equals the forward momentum gained by the rocket
Key Fact

p_total = m₁v₁ + m₂v₂ = constant (when net external force = 0).

Related Terms

Collisions Impulse and momentum Elastic and inelastic collisions Newton's three laws

Study This Concept

Practice conservation of momentum with free review games in these units:

AP Physics 1 Unit 4: Linear Momentum and Collisions Physics Unit 4: Momentum and Collisions