What is invariant mass?

Invariant Mass

The invariant mass, rest mass, intrinsic mass, proper mass, or (in the case of bound systems or objects observed in their center of momentum frame) simply mass, is a characteristic of the total energy and momentum of an object or a system of objects that is the same in all frames of reference related by Lorentz transformations. In the center of momentum frame, the invariant mass of a system is simply the total energy divided by the speed of light squared. In other reference frames, the energy of the system increases, but system momentum is subtracted from this, so that the invariant mass remains unchanged.

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Some articles on invariant mass:

Invariant Mass - Rest Energy
... conclusion about equivalence of energy and mass ... See background for mass-energy equivalence ... hand, the concept of the equivalent Dirac invariant rest mass may be defined in terms of the self energy corresponding to the product of a geometric matter current and a generalized potential as part of a ...
Relativistic Mass Distortion - The Mass of Composite Systems
... The rest mass of a composite system is not the sum of the rest masses of the parts, unless all the parts are at rest ... The total mass of a composite system includes the kinetic energy and field energy in the system ... p of the total momentum vector, the invariant mass is given by In a mathematical system where c = 1, for systems of particles (whether bound or unbound) the total system ...
Center-of-momentum Frame - Properties - Special Relativity
... when divided by the factor c2, where c is the speed of light) therefore gives the rest mass (positive invariant mass) of the system The invariant mass of the system is actually ... Systems which have energy but zero invariant mass (such as photons moving in a single direction, or equivalently, plane electromagnetic waves) do not have COM frames, because there is no frame which they have ...
Relativistic Mass Distortion - Conservation Versus Invariance of Mass in Special Relativity
... for single observers) in systems and in reactions between particles, but rest mass (in the sense of being a sum of particle rest masses) may not be conserved through an ... for isolated systems and single observers, relativistic mass is conserved (each observer sees it constant over time), but is not invariant (that is, different observers see different values) ... Invariant mass, however, is both conserved and invariant (all single observers see the same value, which does not change over time) ...
Relativistic Mass Distortion - Invariant Mass
... The invariant mass is the ratio of four-momentum to four-velocity and is also the ratio of four-acceleration to four-force when the rest mass is constant ...

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