Key Concepts: Conservation of Momentum

The Law of Conservation of Momentum

In an isolated system (no net external force), the total momentum remains constant:

Σp_before = Σp_after

• m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂ (for two objects).
• Applies in all directions independently (conserve x-momentum and y-momentum separately).

Applications

• Collisions: Momentum is conserved in all types (elastic, inelastic, perfectly inelastic).
• Explosions: Total momentum is zero before → total is still zero after (pieces fly in opposite directions).
• Recoil: When a gun fires, bullet and gun have equal and opposite momenta.

Conditions

• External forces (friction, gravity) can break conservation — but during short collisions, their effect is often negligible.