Restenergi

Restenergi, or rest energy, is the energy associated with an object's rest mass in the framework of special relativity. For a particle with rest mass m, the rest energy is defined as E0 = m c^2, where c is the speed of light. In its own rest frame, the particle’s total energy equals this rest energy.

In any other frame, the particle's total energy is E = γ m c^2, with γ = 1 / sqrt(1 − v^2/c^2). The kinetic energy is the difference KE = E − E0. Thus, the total energy includes both rest energy and motion-derived energy, and the rest energy is aframe-invariant quantity tied to the particle’s invariant mass m.

The energy–momentum relationship is E^2 = (pc)^2 + (m c^2)^2, where p is the magnitude of the three-momentum. In the rest frame, p = 0 and E = E0. For particles with nonzero rest mass, E0 > 0; for photons, m = 0, so E0 = 0 and E = pc.

Rest energy also encompasses internal or binding energy in composite systems, so the rest mass M of a bound system satisfies E0 = M c^2. Typical values: electron E0 ≈ 0.511 MeV, proton E0 ≈ 938 MeV; neutrinos have very small E0 due to tiny masses.

Historically, rest energy arises from Einstein’s mass–energy equivalence (1905) and underpins nuclear reactions, particle physics, and astrophysical processes, illustrating how mass and energy are two forms of the same physical quantity.