Editing Mass (section)

== Phenomena ==
There are several distinct phenomena that can be used to measure mass. Although some theorists have speculated that some of these phenomena could be independent of each other,<ref>{{cite magazine |url=https://www.technologyreview.com/2010/06/14/91230/new-quantum-theory-separates-gravitational-and-inertial-mass |title=New Quantum Theory Separates Gravitational and Inertial Mass |magazine=MIT Technology Review |date=14 June 2010|access-date=25 September 2020}}</ref> current experiments have found no difference in results regardless of how it is measured:
* ''Inertial mass'' measures an object's resistance to being accelerated by a force (represented by the relationship [[Newton's laws of motion|{{nowrap|1=''F'' = ''ma''}}]]).
* ''Active gravitational mass'' determines the strength of the gravitational field generated by an object.
* ''Passive gravitational mass'' measures the gravitational force exerted on an object in a known gravitational field.

The mass of an object determines its acceleration in the presence of an applied force. The inertia and the inertial mass describe this property of physical bodies at the qualitative and quantitative level respectively.  According to [[Newton's second law of motion]], if a body of fixed mass ''m'' is subjected to a single force ''F'', its acceleration ''a'' is given by ''F''/''m''. A body's mass also determines the degree to which it generates and is affected by a [[gravitational field]]. If a first body of mass ''m''<sub>A</sub> is placed at a distance ''r'' (center of mass to center of mass) from a second body of mass ''m''<sub>B</sub>, each body is subject to an attractive force {{nowrap|1=''F''<sub>g</sub> = ''Gm''<sub>A</sub>''m''<sub>B</sub>/''r''<sup>2</sup>}}, where {{nowrap|1=''G'' = {{val|6.67|e=-11|u=N⋅kg<sup>−2</sup>⋅m<sup>2</sup>}}}} is the "universal [[gravitational constant]]". This is sometimes referred to as gravitational mass.<ref group="note">When a distinction is necessary, the active and passive gravitational masses may be distinguished.</ref> Repeated experiments since the 17th century have demonstrated that inertial and gravitational mass are identical; since 1915, this observation has been incorporated ''[[A priori and a posteriori|a priori]]'' in the [[equivalence principle]] of [[general relativity]].