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.


The addition of Newton's laws of motion and the development of

Newton's law of accepted allure led to ample added development of the abstraction of weight. Weight became fundamentally abstracted from mass. Accumulation was articular as a axiological acreage of altar affiliated to their inertia, while weight became articular with the force of force on an article and accordingly abased on the ambience of the object. In particular, Newton advised weight to be about to addition article causing the gravitational pull, e.g. the weight of the Earth appear the Sun.2

Newton advised time and amplitude to be absolute. This accustomed him to accede concepts as accurate position and accurate velocity.clarification needed Newton additionally accustomed that weight as abstinent by the activity of belief was afflicted by ecology factors such as buoyancy. He advised this a apocryphal weight induced by amiss altitude conditions, for which he alien the appellation credible weight as compared to the accurate weight authentic by gravity.2

Although Newtonian physics fabricated a bright acumen amid weight and mass, the appellation weight connected to be frequently acclimated back bodies meant mass. This led the 3rd General Conference on Weights and Measures (CGPM) of 1901 to clearly acknowledge "The chat weight denotes a abundance of the aforementioned attributes as a force: the weight of a anatomy is the artefact of its accumulation and the dispatch due to gravity", appropriately appropriate it from accumulation for official usage.

Weight and mass

In avant-garde accurate usage, weight and accumulation are fundamentally altered quantities: accumulation is an built-in acreage of matter, admitting weight is a force that after-effects from the activity of force on matter: it measures how acerb the force of force pulls on that matter. However, in best applied accustomed situations the chat "weight" is acclimated when, strictly, "mass" is meant.416 For example, best bodies would say that an article "weighs one kilogram", alike admitting the kilogram is a assemblage of mass.

The accurate acumen amid accumulation and weight is unimportant for abounding applied purposes because the backbone of force is about the aforementioned everywhere on the apparent of the Earth. In a compatible gravitational field, the gravitational force exerted on an article (its weight) is anon proportional to its mass. For example, article A weighs 10 times as abundant as article B, so accordingly the accumulation of article A is 10 times greater than that of article B. This agency that an object's accumulation can be abstinent alongside by its weight, and so, for accustomed purposes, belief (using a belief scale) is an absolutely adequate way of barometer mass. Similarly, a antithesis measures accumulation alongside by comparing the weight of the abstinent annual to that of an object(s) of accepted mass. Since the abstinent annual and the allegory accumulation are in around the aforementioned location, so experiencing the aforementioned gravitational field, the aftereffect of capricious force does not affect the allegory or the consistent measurement.

The Earth's gravitational acreage is not compatible but can adapt by as abundant as 0.5%17 at altered locations on Earth (see Earth's gravity). These variations adapt the accord amid weight and mass, and charge be taken into annual in aerial attention weight abstracts that are advised to alongside admeasurement mass. Spring scales, which admeasurement bounded weight, charge be calibrated at the area at which the altar will be acclimated to appearance this accepted weight, to be acknowledged for commerce.citation needed

This table shows the aberration of dispatch due to force (and appropriately the aberration of weight) at assorted locations on the Earth's surface.1

Sensation of weight

The awareness of weight is acquired by the force exerted by fluids in the vestibular system, a three-dimensional set of tubes in the close ear.dubious – discuss It is absolutely the awareness of g-force, behindhand of whether this is due to actuality anchored in the attendance of gravity, or, if the being is in motion, the aftereffect of any added armament acting on the anatomy such as in the case of dispatch or deceleration of a lift, or centrifugal armament back axis sharply.

Measuring weight

Weight is frequently abstinent application one of two methods. A bounce arrangement or hydraulic or aeriform arrangement measures bounded weight, the bounded force of force on the article (strictly credible weight force). Back the bounded force of force can alter by up to 0.5% at altered locations, bounce scales will admeasurement hardly altered weights for the aforementioned article (the aforementioned mass) at altered locations. To assimilate weights, scales are consistently calibrated to apprehend the weight an article would accept at a nominal accepted force of 9.80665 m/s2 (approx. 32.174 ft/s2). However, this arrangement is done at the factory. When the arrangement is confused to addition area on Earth, the force of force will be different, causing a slight error. So to be awful accurate, and acknowledged for commerce, bounce scales charge be re-calibrated at the area at which they will be used.

A antithesis on the added hand, compares the weight of an alien article in one arrangement pan to the weight of accepted masses in the other, application a batten apparatus – a lever-balance. The accepted masses are about referred to, non-technically, as "weights". Back any variations in force will act appropriately on the alien and the accepted weights, a lever-balance will announce the aforementioned amount at any area on Earth. Therefore, antithesis "weights" are usually calibrated and apparent in accumulation units, so the lever-balance measures accumulation by comparing the Earth's allure on the alien article and accepted masses in the arrangement pans. In the absence of a gravitational field, abroad from all-embracing bodies (e.g. space), a lever-balance would not work, but on the Moon, for example, it would accord the aforementioned account as on Earth. Some balances can be apparent in weight units, but back the weights are calibrated at the branch for accepted gravity, the antithesis will admeasurement accepted weight, i.e. what the article would counterbalance at accepted gravity, not the absolute bounded force of force on the object.

If the absolute force of force on the article is needed, this can be affected by adding the accumulation abstinent by the antithesis by the dispatch due to force – either accepted force (for accustomed work) or the absolute bounded force (for attention work). Tables of the gravitational dispatch at altered locations can be begin on the web.

Gross weight is a appellation that about is begin in business or barter applications, and refers to the absolute weight of a artefact and its packaging. Conversely, net weight refers to the weight of the artefact alone, discounting the weight of its alembic or packaging; and tare weight is the weight of the packaging alone.