This value was the conventional reference for calculating the kilogram-force, a unit of force whose use has been deprecated since the introduction of SI. The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth's gravity is 980.665 cm/s 2, value already stated in the laws of some countries. ^ In 1901 the third CGPM Archived at the Wayback Machine declared (second resolution) that:.^ BS 350 : Part 1: 1974 Conversion factors and tables, Part 1.^ Acceleration due to gravity varies over the surface of the Earth, generally increasing from about 9.78 m/s 2 (32.1 ft/s 2) at the equator to about 9.83 m/s 2 (32.3 ft/s 2) at the poles.(1978), Introduction to Engineering, Prentice-Hall, ISBN 978-0135018583, LCCN 77024142, archived from the original on, retrieved. ^ IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units), IEEE Std 260.1™-2004 (Revision of IEEE Std 260.1-1993).The SI is an "absolute" metric system with kilogram and meter as base units. "Absolute" systems are coherent systems of units: by using the slug as the unit of mass, the "gravitational" FPS system (left column) avoids the need for such a constant. Note, however, unlike the other systems the force unit is not equal to the mass unit multiplied by the acceleration unit -the use of Newton's second law, F = m ⋅ a, requires another factor, g c, usually taken to be 32.174049 (lb⋅ft)/(lbf⋅s 2). This is convenient because one pound mass exerts one pound force due to gravity. In the "engineering" systems (middle column), the weight of the mass unit (pound-mass) on Earth's surface is approximately equal to the force unit (pound-force). The standard values of acceleration of the standard gravitational field ( g n) and the international avoirdupois pound (lb) result in a pound-force equal toĤ.4482216152605 N.
The pound-force is the product of one avoirdupois pound ( exactly 0.45359237 kg) and the standard acceleration due to gravity, 9.80665 m/s 2 (32.174049 ft/s 2). Product of avoirdupois pound and standard gravity
The 20th century, however, brought the need for a more precise definition, requiring a standardized value for acceleration due to gravity. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from equator to pole by up to half a percent) can safely be neglected. The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Pound-force should not be confused with pound-mass (lb), often simply called pound, which is a unit of mass, nor should these be confused with foot-pound (ft⋅lbf), a unit of energy, or pound-foot (lbf⋅ft), a unit of torque. The pound of force or pound-force (symbol: lbf, sometimes lb f, ) is a unit of force used in some systems of measurement, including English Engineering units and the foot–pound–second system. Pound-forceĮnglish Engineering units, British Gravitational System For the monetary unit, see Pound (currency).
For the basis weight of paper, see Paper density.
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