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The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth.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.
Units for other physical quantities are derived from this set as needed. In English Engineering Units, the pound-mass and the pound-force are distinct base units, and Newton's Second Law of Motion takes the form = where is the acceleration in ft/s 2 and g c = 32.174 lb·ft/(lbf·s 2).
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. [2]
inch-pound force: in lbf ≡ g 0 × 1 lb × 1 in = 0.112 984 829 027 6167 J: joule (SI unit) J The work done when a force of one newton moves the point of its application a distance of one metre in the direction of the force. [32] = 1 J = 1 m⋅N = 1 kg⋅m 2 /s 2 = 1 C⋅V = 1 W⋅s kilocalorie; large calorie: kcal; Cal ≡ 1000 cal IT = 4. ...
Although the pound-force is a coherent derived unit in this system according to the official definition, the system itself is not considered to be coherent because of the presence of the proportionality constant in the force law. A variant of this system applies the unit s 2 /ft to the proportionality constant. This has the effect of ...
The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured.
Maximum force of a molecular motor [8] 10 −11 10 −10 ~160 pN Force to break a typical noncovalent bond [8] 10 −9 nanonewton (nN) ~1.6 nN Force to break a typical covalent bond [8] 10 −8 ~82nN Force on an electron in a hydrogen atom [1] 10 −7 ~200nN Force between two 1 meter long conductors, 1 meter apart by an outdated definition of ...
In the operational definition, the weight of an object is the force measured by the operation of weighing it, which is the force it exerts on its support. [10] Since W is the downward force on the body by the centre of earth and there is no acceleration in the body, there exists an opposite and equal force by the support on the body. Also it is ...