rest mass

American  

noun

Physics.

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

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rest mass British  

noun

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

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rest mass Scientific  

1. In Special and General Relativity, the observed mass of a body that is not in motion with respect to the observer.

2. Also called invariant mass

3. Compare relativistic mass

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Etymology

Origin of rest mass

First recorded in 1910–15

Example Sentences

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

From BBC • Jan. 26, 2016

First, total energy is related to momentum and rest mass.

From Textbooks • Aug. 12, 2015

It is infinite in range because its carrier particle, the graviton, has zero rest mass.

From Textbooks • Aug. 12, 2015

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

From Scientific American • Oct. 14, 2013

It would have produced ten thousand million times as much energy as the total disintegration of the rest mass would have produced!

From Hanging by a Thread by Garrett, Randall