What (who) is massed - definition
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![1285 BCE}}). The scene shows [[Anubis]] weighing the heart of Hunefer.](https://commons.wikimedia.org/wiki/Special:FilePath/El pesado del corazón en el Papiro de Hunefer.jpg?width=200 "1285 BCE}}). The scene shows [[Anubis]] weighing the heart of Hunefer.")
![Massmeter, a device for measuring the inertial mass of an astronaut in weightlessness. The mass is calculated via the oscillation period for a spring with the astronaut attached ([[Tsiolkovsky State Museum of the History of Cosmonautics]]).](https://commons.wikimedia.org/wiki/Special:FilePath/Massmeter.jpg?width=200 "Massmeter, a device for measuring the inertial mass of an astronaut in weightlessness. The mass is calculated via the oscillation period for a spring with the astronaut attached ([[Tsiolkovsky State Museum of the History of Cosmonautics]]).")
![intermediate speeds]], it will revolve around Earth along an elliptical orbit (C, D). Beyond the [[escape velocity]], it will leave the Earth without returning (E).](https://commons.wikimedia.org/wiki/Special:FilePath/Newton Cannon.svg?width=200 "intermediate speeds]], it will revolve around Earth along an elliptical orbit (C, D). Beyond the [[escape velocity]], it will leave the Earth without returning (E).")
![The kilogram is one of the seven [[SI base units]].](https://commons.wikimedia.org/wiki/Special:FilePath/SI base unit.svg?width=200 "The kilogram is one of the seven [[SI base units]].")
Wikipedia
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Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementary particles, theoretically with the same amount of matter, have nonetheless different masses. Mass in modern physics has multiple definitions which are conceptually distinct, but physically equivalent. Mass can be experimentally defined as a measure of the body's inertia, meaning the resistance to acceleration (change of velocity) when a net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies.
The SI base unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.
