User:Milton Beychok/Sandbox2

The pound-force (symbol: lbf from the Latin libra for pound and the symbol f for force) is a measurement|unit of force used primarily in the United States. It is equivalent to exactly 4.4482216152605 newtons. In most contexts, the shorter name "pound" is used, but this can introduce confusion with the mass unit of the similar name.

Definitions

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 place to place by up to half a percent) can safely be neglected.

The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed. Today, in accordance with the General Conference on Weights and Measures, standard gravity is usually taken to be 9.80665 m/s² (32.174 049 ft/s²).