In order to suppress the electrostatic and magnetic field effects, ultrathin metal wires are often employed for discharging the proof mass which is used in a highprecision space electrostatic accelerometer or gravitational experiments. This wire introduces a thermal noise limit based on fluctuation-dissipation theory, which depends upon its stiffness and structural loss. In this paper, a simple method for measuring the stiffness and the loss angle of a thin discharging wire is presented by connecting it to a pendulum suspended by a high-quality silica fiber with negligible dissipation. The stiffness and the loss angle of a 10 μm gold wire are measured; the experimental results agree with theoretical estimation. The thermal noise of the pendulum with a thin discharging wire is estimated, and its possible applications in the gravitational experiments are also discussed.

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