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Rest energy
Intermediate
Mass is energy.
E₀ = mc²E₀ = mc² means mass is concentrated energy: 1 kg = 9×10¹⁶ J. In reactions, mass changes appear as released energy.
Electron: 0.511 MeV; proton: 938 MeV.
Mass isn't converted into something else; it is the energy content in the rest frame.
In more detail
The rest energy of a particle is E0 = mc², the energy it has when not moving. This equivalence of mass and energy is one of the most famous results of relativity.
Real-world uses
- Nuclear reactions convert small amounts of mass into large amounts of energy.
- The electron's rest energy is about 0.511 MeV.
- Nuclear physicists use rest energy to estimate the energy released when mass disappears in a reaction.
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Frequently asked questions
Is mass really energy?
Mass and energy are equivalent, so mass can be converted into energy and back.
How much energy is in a gram?
About 9 × 10¹³ joules, roughly the energy of a large bomb.
Does mass really become energy?
In reactions, the mass of the products is less than that of the reactants, and the difference appears as energy.
Related topics in Relativity
Proper time · Relativistic momentum · Relativistic energy · Energy–momentum relation · Relativistic kinetic energy · Massless particles