Relativistic energy, momentum and invariant mass
A particle of invariant mass m has p=γ_u m u, E=γ_u mc² and K=(γ_u−1)mc²; E²−|p|²c²=m²c⁴.
Key knowledge
A particle of invariant mass m has p=γ_u m u, E=γ_u mc² and K=(γ_u−1)mc²; E²−|p|²c²=m²c⁴. For a massless particle the invariant relation gives E=c|p|. Total four-momentum is conserved for a closed interaction and determines a system's invariant mass.
Values and equations
p=γ_u m u; E=γ_u mc²; K=(γ_u−1)mc²; E²−|p|²c²=m²c⁴
- p
- Momentum kg m s⁻¹
- E,K
- Total/kinetic energy J
- m
- Invariant mass kg
- u,c
- Particle/light velocities or speed m s⁻¹
- γ_u
- Dimensionless particle Lorentz factor
Conditions and scope
- Flat-spacetime particle kinematics with positive energy and fixed invariant mass; massive formula uses u<c.
- m is invariant mass, not velocity-dependent relativistic mass. Internal kinetic and binding energies affect a composite system's mass; total energy is frame dependent.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Classical Electromagnetism (2014): Relativistic particle dynamics: Equations 1839–1847: momentum and energy four-vector, translating source m₀ into invariant m. University Physics 3 §5.9: Relativistic energy/momentum invariant and kinetic-energy relation.
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Entry details
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