Electrostatic damping and its effect on precision mechanical experiments

We develop a model for damping of a mechanical oscillator when subjected to an electrostatic force applied via electrodes with resistive losses. The m odel predicts viscous damping that varies as the inverse of oscillation fre quency and that is proportional to a dimensionless constant Delta(e), which depends on the surface properties of the electrodes. Preliminary experimen ts made using a torsion strip pendulum with aluminium electrodes establish that 2.2(5) x 10(-3) > Delta(e) > 5.9(3.4) x 10(-6) depending on the time s pent under vacuum. Finally we calculate the magnitude of error that such lo sses produce in certain determinations of Newton's constant of gravitation where an electrostatic torque calibration is employed. (C) 1999 Published b y Elsevier Science B.V. All rights reserved.