Tuesday, 13 March 2012


In science and engineering, the weight of an article is the force on the article due to gravity.12 Its consequence (a scalar quantity), generally denoted by an italic letter W, is the artefact of the accumulation m of the article and the consequence of the bounded gravitational dispatch g;3 thus: W = mg. Back advised a vector, weight is generally denoted by a adventurous letter W. The assemblage of altitude for weight is that of force, which in the International System of Units (SI) is the newton. For example, an article with a accumulation of one kilogram has a weight of about 9.8 newtons on the apparent of the Earth, about one-sixth as abundant on the Moon, and actual about aught back in abysmal amplitude far abroad from all bodies imparting gravitational influence.

In adverse to this "purely gravitational" definition, some books use an "operational" definition,citation needed defining the weight of an article as the force abstinent by the operation of belief it (using a force-sensitive scale, such as a bounce scale), in vacuum. This is the force an article exerts on a scale, and is according to the force appropriate to abutment it (although in the adverse administration to the "weight" force). This force abstinent by force-scales is the aforementioned as what some added sources appellation the object's "apparent weight".

These two definitions of weight differ, sometimes dramatically, back added factors arbitrate so that the force appropriate to abutment a anatomy is not absolutely according and adverse to the gravitational force acting on it. For example, in the operational definition, a mechanically accelerated article or being (as in an elevator, dragster or rocket) has a capricious weight due to its capricious able dispatch (or g-force). However, according to the absolutely gravitational analogue its weight does not change back force still exerts the aforementioned force (g in the blueprint W = mg is unchanged). In the case of an article in chargeless fall, such as a falling apple, or an astronaut in an orbiting spacecraft, the operational analogue says that the weight is zero. This is in befitting with the accustomed abstraction that such altar are "weightless", and the actuality that a calibration indicates a aught weight as the anatomy exerts no force on it. In contrast, by the absolutely gravitational definition, a body's weight in chargeless abatement is the aforementioned as if the anatomy were at rest, afresh because, in the Newtonian approach of gravitation, the gravitational force acting on the anatomy is unchanged.

In accustomed applied usage, including bartering usage, the appellation "weight" is frequently acclimated to beggarly mass, which scientifically is an absolutely altered concept.4 On the apparent of the Earth, the dispatch due to force (the "strength of gravity") is about constant; this agency that the arrangement of the weight force of a apoplectic article on the apparent of the Earth to its accumulation is about absolute of its location, so that an object's weight force can angle as a proxy for its mass, and carnality versa.

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