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A quantitative measure of the resistance of an object to attempts to change its velocity. Mass is often defined as Hence mass is a measure of inertia (from the Latin vis inertia, the force of inaction.) |
Newton equated mass and "quantity of matter in a body. Gravitational Mass, which appears in the Law of Gravitation, is identical to this Inertial Mass. A proper explanation of this involves the Principle of Equivalence and General Relativity, and is beyond the scope of this introductory wiki. The interested student is directed toward books on relativity, or to look up these terms on the internet. ", which he said arises "from its density and bulk conjointly."
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_Gravitational Mass_, which appears in the Law of [Gravitation], has been shown to be proportional to _Inertial Mass_ to better than one part per trillion. \[See Eotvos experiment, http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment, much more accurately performed at the University of Washington - _Physical Review Letters 100, 041101 (2008)_.\] 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. |