What (who) is heaviness - definition
![Ancient Greek]] official bronze weights dating from around the 6th century BC, exhibited in the [[Ancient Agora Museum]] in Athens, housed in the [[Stoa of Attalus]].](https://commons.wikimedia.org/wiki/Special:FilePath/3199 - Athens - Stoà of Attalus Museum - Bronze weights - Photo by Giovanni Dall'Orto, Nov 9 2009.jpg?width=200 "Ancient Greek]] official bronze weights dating from around the 6th century BC, exhibited in the [[Ancient Agora Museum]] in Athens, housed in the [[Stoa of Attalus]].")
![0}} in 0.86 seconds. This is a horizontal acceleration of 5.3{{spaces}}g. Combined with the vertical g-force in the stationary case the [[Pythagorean theorem]] yields a g-force of 5.4{{spaces}}g. It is this g-force that causes the driver's weight if one uses the operational definition. If one uses the gravitational definition, the driver's weight is unchanged by the motion of the car.](https://commons.wikimedia.org/wiki/Special:FilePath/Nitrolympics TopFuel 2005.jpg?width=200 "0}} in 0.86 seconds. This is a horizontal acceleration of 5.3{{spaces}}g. Combined with the vertical g-force in the stationary case the [[Pythagorean theorem]] yields a g-force of 5.4{{spaces}}g. It is this g-force that causes the driver's weight if one uses the operational definition. If one uses the gravitational definition, the driver's weight is unchanged by the motion of the car.")
![A [[weighbridge]], used for weighing trucks](https://commons.wikimedia.org/wiki/Special:FilePath/Peso-Valdivia-dsc02545.jpg?width=200 "A [[weighbridge]], used for weighing trucks")
![moments]] acting on it sum to zero).](https://commons.wikimedia.org/wiki/Special:FilePath/WeightNormal.svg?width=200 "moments]] acting on it sum to zero).")
Wikipedia
In science and engineering, the weight of an object is the force acting on the object due to acceleration or gravity.
Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Yet others define it as the magnitude of the reaction force exerted on a body by mechanisms that counteract the effects of gravity: the weight is the quantity that is measured by, for example, a spring scale. Thus, in a state of free fall, the weight would be zero. In this sense of weight, terrestrial objects can be weightless: ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, would be weightless.
The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, and about one-sixth as much on the Moon. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use (e.g. comparing and converting force weight in pounds to mass in kilograms and vice versa).
Further complications in elucidating the various concepts of weight have to do with the theory of relativity according to which gravity is modeled as a consequence of the curvature of spacetime. In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.
