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A quantitative measure of the resistance of an object to attempts to change its velocity. Hence mass is a measure of inertia (from the Latin vis inertia, the force of inaction.) |
Newton equated mass and "quantity of matter", which he said arises "from its density and bulk conjointly."
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_Gravitational Mass_, which appears in the Law of [gravitation (universal)], has been shown to be proportional to _Inertial Mass_ to better than one part per trillion. \[See the [Eotvos experiment page in Wikipedia|http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment], much more accurately performed at the University of Washington - _Physical Review Letters 100, 041101 (2008)_.\] This equality is assumed by the _Principle of Equivalence_ and is a cornerstone of Einstein's theory of _General Relativity_. This theory indicates that all forms of energy have mass via the relationship E=mc2. |
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