p = mv — Momentum = mass × velocity
F = Δp / Δt — Force from change in momentum
m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂ — Conservation of momentum (elastic collisions)
m₁u₁ + m₂u₂ = (m₁ + m₂)v — Inelastic collisions