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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.
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. ...
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).
The pound-force provides an alternative unit of mass: one slug is the mass that will accelerate by one foot per second squared when acted on by one pound-force. [58] An alternative unit of force in a different foot–pound–second system, the absolute fps system, is the poundal , defined as the force required to accelerate a one-pound mass at ...
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.
became crucial. This type of performance evaluation required the definition of both particular standards and broader objectives in the pursuit of educational goals. Second, these standards and assessment-based reforms also included the involvement and feedback of various stakeholders in both the public and the private sector.
In United States customary units, the pound can be either a unit of force or a unit of mass. [24] Related units used in some distinct, separate subsystems of units include the poundal and the slug. The poundal is defined as the force necessary to accelerate an object of one-pound mass at 1 ft/s 2, and is equivalent to about 1/32.2 of a pound-force.