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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.
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Origin of rest mass

First recorded in 1910–15
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for rest mass

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
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

rest mass in Medicine

rest mass

n.
  1. The physical mass of a body when it is regarded as being at rest.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

rest mass in Science

rest mass

  1. 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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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.