rest mass
noun
: the mass of a body exclusive of additional mass the body acquires by its motion according to the theory of relativity
Examples of rest mass in a Sentence
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Those electromagnetic waves carry energy away from the system of charges and fields, conserving the total energy of the system (including rest mass energy through Einstein’s E = mc) as well as the system’s total momentum.
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Big Think, 7 Nov. 2025
When the temperature of the Universe drops below a certain, critical threshold — a threshold set by the rest mass of each particle — fewer and fewer collisions occur that have enough energy to allow for creation to be a possibility.
—Ethan Siegel, Forbes, 2 Sep. 2021
All these experiments measure energy, but that's pretty much the same as the rest mass of the particle.
—Phil Plait, Discover Magazine, 13 Dec. 2011
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Big Think, 7 Nov. 2025
When the temperature of the Universe drops below a certain, critical threshold — a threshold set by the rest mass of each particle — fewer and fewer collisions occur that have enough energy to allow for creation to be a possibility.
—Ethan Siegel, Forbes, 2 Sep. 2021
All these experiments measure energy, but that's pretty much the same as the rest mass of the particle.
—Phil Plait, Discover Magazine, 13 Dec. 2011
Cite this Entry
“Rest mass.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/rest%20mass. Accessed 13 Nov. 2025.
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