total p before = total p after when net external force = 0 m₁v₁ᵢ + m₂v₂ᵢ = m₁v₁f + m₂v₂f
Total Momentum (before)
0.0 kg·m/s
After: — kg·m/s
Object 1 (blue)
m₁3.0 kg
v₁ᵢ+6.0 m/s
Object 2 (amber)
m₂5.0 kg
v₂ᵢ0.0 m/s
p₁ᵢ = m₁v₁ᵢ—
p₂ᵢ = m₂v₂ᵢ—
Σpᵢ (total)—
net F = 0 → momentum conserved
internal forces cancel in pairs
works for explosions & collisions
applies to systems of any size
Σpᵢ = Σpf: when no net external force acts on a system, total momentum is conserved. The momentum objects exchange with each other stays inside the system.