masaenergie

Masaenergie, or mass-energy equivalence, is the principle in physics that mass and energy are two forms of the same quantity. In special relativity, the total energy E of a particle with rest mass m0 and momentum p relates as E^2 = (pc)^2 + (m0 c^2)^2. When the particle is at rest (p = 0), its energy equals its rest energy E0 = m0 c^2. This leads to the statement that mass can be converted into energy and energy into mass, as seen in nuclear reactions, particle creation, and annihilation processes. The relation also implies that a moving object has kinetic energy E - E0 = (gamma - 1) m0 c^2, where gamma = 1 / sqrt(1 - v^2/c^2). Modern descriptions emphasize invariant rest mass rather than “relativistic mass,” since only E and p change with frame.

The concept explains nuclear binding energy: the binding energy increases when a nucleus forms, and the mass of the bound system is smaller than the sum of its parts by Δm c^2. It also underlies phenomena such as electron-positron annihilation into photons and particle production in high-energy collisions, where sufficient energy is converted to mass of new particles.

Masaenergie forms a cornerstone of high-energy physics, astrophysics, and medical imaging technologies relying on energy–mass conversion, and it remains a central example of the equivalence of mass and energy in modern physics.