8.3 Weight
In science and technology, the weight of a body in a particular reference frame is defined as the force that gives the body an acceleration equal to the local acceleration of free fall in that reference frame [4: ISO 80000-4]. Thus the SI unit of the quantity weight defined in this way is the newton (N). When the reference frame is a celestial object, Earth for example, the weight of a body is commonly called the local force of gravity on the body.
Example: The local force of gravity on a copper sphere of mass 10 kg located on the surface of the Earth, which is its weight at that location, is approximately 98 N.
Note: The local force of gravity on a body, that is, its weight, consists of the resultant of all the gravitational forces acting on the body and the local centrifugal force due to the rotation of the celestial object. The effect of atmospheric buoyancy is usually excluded, and thus the weight of a body is generally the local force of gravity on the body in vacuum.
In commercial and everyday use, and especially in common parlance, weight is usually used as a synonym for mass. Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the verb ?to weigh? means ?to determine the mass of? or ?to have a mass of.?
Examples: the child?s weight is 23 kg the briefcase weighs 6 kg Net wt. 227 g
Inasmuch as NIST is a scientific and technical organization, the word ?weight? used in the everyday sense (that is, to mean mass) should appear only occasionally in NIST publications; the word ?mass? should be used instead. In any case, in order to avoid confusion, whenever the word ?weight? is used, it should be made clear which meaning is intended.