mass

A quantitative measure of the resistance of an object to attempts to change its velocity.



Mass is often defined as a measure of the 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.