Mass (physics)

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This article is only a brief description of the subject, and is not intended to give a full explanation.
Check out the "see also" or "references" sections, or Wikipedia's article for more detail.
For the Roman Catholic service, see mass (religion)

Mass is a fundamental concept in physics, roughly corresponding to the intuitive idea of "how much matter there is in an object." On a more fundamental level, mass is equivalent to inertia, which is the resistance of an object to change velocity when acted upon by a force. When measured at the surface of the Earth, "weight" is the colloquial term for mass (though weight is really a force calculated as mass times acceleration due to gravity. The Imperial unit for mass is not the pound, but the slug). In free-fall, an object has no weight, but it retains its mass as well as its inertia.

Mass is a central concept in classical mechanics and related subjects, and there are several definitions of mass within the framework of relativistic kinematics. In the theory of relativity, the quantity invariant mass, which in concept is close to the classical idea of mass, does not vary between single observers in different reference frames.

If one is not careful, mass can be converted into energy. If it's far enough away, it can provide a nice pleasant warm glow. If it's too close and not carefully contained, it can burn.

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