A 10000 times enlarged hydrodynamic model of the outer hair cell stereocila in the inner ear was built. On the model it was possible to measure the force and the force direction for each individual hair as a function of the flow direction and velocity. Measurement were made at the mean flow velocity 10-2 m/s, which is equivalent to a flow velocity in the real ear of about 1 μm/s. The kinematic viscosity of the liquid used in the model was 10000 times higher than the viscosity of perilymph to attain hydrodynamic equality. Two different geometries for the stereocilia pattern were tested. First the force distribution for a W-shaped stereocilia pattern was recorded. This is the stereocilia pattern found in all real ears. It was found that the forces acting on the hairs were very regular and perpendicular to the legs of the W when the flow was directed from the outside of the W. When the flow was reversed, the forces were not reversed, but were much more irregular. This can eventually explain the half wave rectification of the nerve signals. As a second experiment, the force distribution for a V-shaped stereocilia pattern was recorded. Here the forces were irregular both when the flow was directed into the V and when it was directed against the edge of the V