Linear Momentum

Linear momentum p of a particle: p = m·v. Vector quantity. Units: kg·m/s.

Newton's 2nd law (general form): F = dp/dt. For constant mass: F = m·a.

Total momentum of a system: P = Σ m_i·v_i.

Momentum of a SYSTEM = M·V_COM. So COM moves as if all momentum were a single point particle.

Conservation: if net external force = 0, total P is conserved.

Internal forces in a system change individual momenta but DO NOT change total momentum.

Photons have momentum p = h/λ (no rest mass).

Relativistic momentum: p = γmv = mv/√(1−v²/c²). Reduces to mv for v ≪ c.