Balances

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Emperor Jahangir  (reign  (reign !"# $ !%&' weighing his son hah Jahan on Jahan on a weighing scale )y artist *anohar (+ !#, *ughal dynasty, -ndia'. + weighing scale (usually ust /scales/ in 01 and +ustralian English, /weighing machine/ in south +sian +sian English or /scale/ in 0 English' is a measuring instrument for instrument for determining the weight or weight  or mass mass of  of an o)ect. + spring scale measures scale measures weight )y the distance a spring spring deflects  deflects under its load. + balance compares the tor2ue on the arm due to the sample weight to the tor2ue on the arm due to a standard reference weight using a hori3ontal lever . 4alances are different from scales, in that a )alance measures mass mass (or  (or more specifically gravitational mass', mass', where as a scale measures weight (or weight  (or more specifically, specifically, either the tension tension or   or compression compression force force of  of constraint provided  )y the scale'. Weigh Weighing ing scales are used used in many industrial industrial and commercial commercial applications, and  products from feathers feathers to loaded tractor$trailers tractor$trailers are sold )y weight. weight. peciali3ed medical medical scales and )athroom scales are used to measure the  )ody weight of weight of human )eings.

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 5istory

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% 4alance

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%. +nalytical )alance

6 cales o

6. pring scales

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6.% 7endulum )alance scales

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6.6 Electronic analytical /)alance/ scale

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6.8 train gauge scale

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6.# 5ydraulic or pneumatic scale

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8 Testing and certification

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# upermarket9retail scale

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! ources of error 

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& ym)olism

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 ee also

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; Footnotes

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" E The oldest evidence for the e  -n its traditional form, it consists of a pivoted hori3ontal lever  of e2ual length arms, called the )eam, with a weighing pan, also called  scale, scalepan, or bason (o)solete=%>', suspended from each arm (which is the origin of the originally plural term /scales / for a weighing instrument'. The unknown mass is placed in one pan, and standard masses are added to the other pan until the )eam is as close to e2uili)rium as  possi)le. -n precision )alances, a slider mass is moved along a graduated scale. The slider  position gives a fine correction to the mass value. +lthough a )alance technically compares

weights, not masses, the weight of an o)ect is proportional to its mass, and the standard weights used with )alances are usually la)eled in mass units.

Two "$decagram masses

*asses of #", %", , %, # and " gram 4alances are used for precision mass measurement, )ecause unlike spring scales their accuracy is not affected )y differences in the local gravity, which can vary )y almost ".#C =6> at different locations on Earth. + change in the strength of the gravitational field caused )y moving the )alance will not change the measured mass, )ecause the moments of force on either side of the )alance )eam are affected e2ually. -n fact, a )alance will measure the correct mass even on other planets or moons, or any location that e, and is commonly used for cali)rating test weights. To reduce the need for large reference masses, an off$center )eam can )e used. + )alance with an off$center )eam can )e almost as accurate as a scale with a center )eam, )ut the off$

center )eam re2uires special reference masses and cannot )e intrinsically checked for accuracy )y simply swapping the contents of the pans as a center$)eam )alance can. To reduce the need for small graduated reference masses, a sliding weight called a poise can )e installed so that it can )e positioned along a cali)rated scale. + poise adds further intricacies to the cali)ration procedure, since the e

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Error in mass of reference weight

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+ir gusts, even small ones, which push the scale up or down

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Friction in the moving components that cause the scale to reach e2uili)rium at a different configuration than a frictionless e2uili)rium should occur.

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ettling air)orne dust contri)uting to the weight

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*is$cali)ration over time, due to drift in the circuitDs accuracy, or temperature change

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*is$aligned mechanical components due to thermal e cales are also the sym)ol for the astrological sign Bi)ra.

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