force measurements on a scaled hair - bundle model respected the physiological character of the liquid flow . the finite - element method provided approximate solutions to partial differential equations reflecting the hair bundle 's geometry . the velocity variable of the liquid was substituted by the time derivative of the displacement ; fluid pressure was approximated by linear shape functions and the displacements of liquid and solid by quadratic ones . the hydrodynamic forces between stereocilia were estimated analytically by solving the stefan - reynolds equations under the lubrication approximation , which is valid when the gaps between adjacent stereocilia are much smaller than their diameter . stochastic simulations based on these results were performed for a system of linearly coupled dynamic variables following a langevin description with gaussian white noise at room temperature . the integration procedure was validated by choosing time steps small enough to assure that the results were independent of the increment . we tested the effects of inertia and of the estimated top - connecter stiffness and confirmed the validity of our conclusions for mammalian hair bundles . dual - beam differential interferometry was used to record stereociliary motions with sub - nanometre spatial and sub - millisecond temporal resolution . fourier analysis of the records was performed with the multitaper method to obtain coherence spectra as well as stiffness and drag coefficients . these results were used to verify the predictions of the numerical model and to measure directly the relative mode of motion between stereocilia .