torsion balance

an instrument for measuring small forces, as electric attraction or repulsion, by determining the amount of torsion or twisting they cause in a slender wire or filament.

[1820-30]

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Device used to measure the gravitational acceleration at the Earth's surface.

It consists essentially of two small masses at different elevations that are supported at opposite ends of a beam. The latter is suspended from a wire that twists because the masses are affected differently by the force of gravity. When the wire is twisted, an optical system indicates the angle of deflection, and the torque, or twisting force, can be calculated. The torque is correlated with the gravitational force at the point of observation. Torsion balance may also refer to a device used in weighing, a type of equal-arm balance.

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▪ measurement instrument

      device used to measure the gravitational acceleration at the Earth's surface. Other such devices, using different methods to obtain the same result, are pendulums and gravimeters. The torsion balance consists essentially of two small masses at different elevations that are supported at opposite ends of a beam. The latter is suspended from a wire that undergoes torsion because the masses are affected differently by the force of gravity. When the wire is twisted, an optical system indicates the angular deflection (θ), and the torque (T), or twisting force, involved can be calculated from the simple expression T = kθ, in which k is a constant that depends on the properties of the instrument. The amount of torque, in turn, is correlated with the gravitational force at the point of observation. The torsion balance was devised by Lóránt von Eötvös, a Hungarian physicist, in 1902; many scientists have contributed modifications to the basic instrument.

      The term torsion balance also refers to a device used in weighing, an equal arm balance that uses horizontal steel bands instead of pivots and bearings.

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