E = mc² Explorer
Adjust mass and speed (as a fraction of c) to see how rest energy and relativistic total energy respond.
Mass (kg)1.000
Velocity (v / c)0.000
Live Statistics
Rest energy E₀ = mc²
0 J
Lorentz factor γ
1.000
Total energy E = γmc²
0 J
Kinetic energy Eₖ = (γ−1)mc²
0 J
Relativistic mass γm
0 kg
E = mc² — a stationary mass m carries a rest energy E₀ = mc². When it moves at speed v, its total energy grows to E = γmc², where γ = 1 / √(1 − v²/c²). As v approaches c, γ → ∞ and an infinite amount of energy would be needed to reach light speed — which is why nothing with mass ever does.