REST MASS Definition & Meaning

rest mass

noun

Physics.

the mass of a body as measured when the body is at rest relative to an observer, an inherent property of the body.

rest mass

noun

the mass of an object that is at rest relative to an observer. It is the mass used in Newtonian mechanics

rest mass

In Special and General Relativity, the observed mass of a body that is not in motion with respect to the observer.
Also called invariant mass
Compare relativistic mass

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�y��vlog History and Origins

Origin of rest mass¹

First recorded in 1910–15

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Example Sentences

Examples have not been reviewed.

Consequently, its accretion disk glows brightly, radiating away about a tenth of its rest mass and exceeding by orders of magnitude the total luminosity from stars in its host galaxy.

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Nuclear processes could not account for their energy output, because they release only a percent fraction of their rest mass as pure energy.

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Electrons have no known substructure; they’re defined solely by their rest mass, spin, and charge, which are the same for every electron.

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It carries energy proportional to the radiation frequency but has zero rest mass.

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And all along we’ve not quite managed to pin down their actual stationary mass, although it must be small, probably less than a millionth of the rest mass of an electron.

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