Demonstration of the minimal coupling of horizontal accelerations to rotations in a torsion balance suspended from three wires.

Abstract

Cavendish-type torsion balances have high sensitivity for measuring forces over ranges of a few centimeters and more, but their dynamics make it difficult to extend this range to much less than fractions of a millimeter. For example, the atomic force microscope is often used in favor of the torsion balance to measure the short-range Casimir force. We present the results of a study of a simple torsion balance with a three-wire suspension. The constraints of the three wires offer the possibility of maintaining parallelism between flat plates with areas of a few ∼cm2 at separations of ≤10μm, which could potentially be useful for precision studies of short-range forces. We develop and discuss simple analytical models of the three-wire torsion balance and describe an experimental investigation into the coupling of ground tilt (and by inference horizontal acceleration) to its torsional rotation. We show that, like the Cavendish-type torsion balance, the three-wire torsion balance is highly insensitive to tilts and that the most significant coupling is due to the differences in lengths of the suspension wires. We also demonstrate that the tilt sensitivity changes linearly with the differences in the wire lengths due to small tension changes corresponding to displacements of the center of mass.