# rest mass

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## Rest mass

A constant intrinsic to a body which determines its inertial and energy-momentum properties. It is a fundamental concept of special relativity, and in particular it determines the internal energy content of a body. It is the same as the inertial mass of classical mechanics. According to the principle of equivalence, the basic physical principle of general relativity, the inertial mass of a body is also equal to its gravitational mass. See Classical mechanics, Gravitation, Relativity

The rest mass or inertial mass of a body, m, is a measure of its resistance to being accelerated at a by a force F ; in classical mechanics the relation between inertial mass, acceleration, and force is given by Newton's law, Eq. (1).

(1) In special relativity Newton's law holds exactly only in the body's rest frame, that is, the frame in which the body is instantaneously at rest. See Newton's laws of motion

Associated with the rest mass of a body, there is an internal or rest energy. In the system where the body is at rest, the energy of the body is given

(2) by Eq. (2).

The experimental realization of the interconversion of mass and energy is accomplished in the reactions of nuclei and elementary particles. In particular, the energy source of nuclear bombs and nuclear fission reactors is a small decrease in the total mass of the interacting nuclei, which gives rise to a large energy release because of the large numerical value of c2. See Elementary particle, Nuclear fission

## rest mass

The mass of an elementary particle, etc., when at rest. According to the special theory of relativity, a body's mass increases as its speed increases. This is noticeable only at speeds close to the speed of light. Rest mass is often expressed in MeV (megaelectronvolts).

## rest mass

[′rest ‚mas]
(relativity)
The mass of a particle in a Lorentz reference frame in which it is at rest.
References in periodicals archive ?
Statement 1 The velocity u' of the particle with a non-zero rest mass is always less than the velocity c' of light that moves in the same direction:
By comparison the lightest known particle, the electron, has a rest mass of 511,000 eV.
Due to the RQED theory of axisymmetric particle-shaped steady states with rest mass, a separable generating function
Recent theories of particle physics and cosmology would like them to have a small rest mass nevertheless.
The exceptions have been some experiments in the Soviet Union that persist in showing a neutrino rest mass of 30 or 40 electron-volts (eV).
Another suggestion that could solvethe solar puzzle in a somewhat roundabout way requires neutrinos to have a very small rest mass.
But the net elementary charge, e, and the finite electron rest mass, [m.
Energy seemed to be disappearing unaccountably, and to save the law of conservation of energy Pauli suggested the existence of a particle that was electrically neutral, had no rest mass and interacted so feebly with other matter that it was almost undetectable.
Two trillion electron-volts (2 TeV) equals the rest mass of somewhat more than 2,000 protons.
As stated in a review by Quigg  among others, the Higgs boson is a particle of zero electric charge and nonzero rest mass.

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