rest mass

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.

rest mass

noun

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

rest mass

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

Word History and Origins

Origin of rest mass¹

First recorded in 1910–15