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Usually, the relationship between mass and weight on Earth is highly proportional; objects that are a hundred times more massive than a one-liter bottle of soda almost always weigh a hundred times more—approximately 1,000 newtons, which is the weight one would expect on Earth from an object with a mass slightly greater than 100 kilograms.
The pound or pound-mass is a unit of mass used in both the British imperial and United States customary systems of measurement.Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.453 592 37 kilograms, and which is divided into 16 avoirdupois ounces. [1]
Systems of measure either define mass and derive a force unit or define a base force and derive a mass unit [1] (cf. poundal, a derived unit of force in a mass-based system). A slug is defined as a mass that is accelerated by 1 ft/s 2 when a net force of one pound (lbf) is exerted on it.
the slug (sl), an Imperial unit of mass (about 14.6 kg) the pound (lb), a unit of mass (about 0.45 kg), which is used alongside the similarly named pound (force) (about 4.5 N), a unit of force [note 3] the Planck mass (about 2.18 × 10 −8 kg), a quantity derived from fundamental constants
The avoirdupois units of mass and weight differ for units larger than a pound (lb). The British imperial system uses a stone of 14 lb, a long hundredweight of 112 lb and a long ton of 2,240 lb. The stone is not a measurement of weight used in the US.
The International Committee for Weights and Measures (CIPM) approved a revision in November 2018 that defines the kilogram by defining the Planck constant to be exactly 6.626 070 15 × 10 −34 kg⋅m 2 ⋅s −1, effectively defining the kilogram in terms of the second and the metre. The new definition took effect on 20 May 2019.
These variations alter the relationship between weight and mass, and must be taken into account in high-precision weight measurements that are intended to indirectly measure mass. Spring scales , which measure local weight, must be calibrated at the location at which the objects will be used to show this standard weight, to be legal for commerce.
In July 1959, the various national foot and avoirdupois pound standards were replaced by the international foot of precisely 0.3048 m and the international pound of precisely 0.453 592 37 kg, making conversion between the systems a matter of simple arithmetic.