Damping of a pendulum: An experimental test of the Stokesian unsteady friction force on a cylinder

In 1851, Stokes (in insert) calculated the friction force on a cylinder in oscillating motion, neglecting nonlinear term of Navier-Stokes equation, an approximation valid for vanishing values Reynolds number Re. Previous tests were performed with Re>0.1 and frequently Re>>1. We have measured oscillation macroscopic gravity pendulum. Our position detector submicrometer sensitivity enables us to record very small amplitudes, corresponding Re=0.0002. The deduced from damping time constant is good agreement Stokes' calculation.