Capillary-gravity wave resistance in ordinary and magnetic fluids

Wave resistance is the drag force associated to the emission of waves by a moving disturbance at a free fluid surface. In the case of capillary-gravity waves it undergoes a transition from zero to a finite value as the speed of the disturbance reaches a certain critical value. For the first time an experiment is designed in order to obtain the capillary-gravity wave resistance as a function of speed. The effect of viscosity is explored, and a magnetic fluid is used to extend the available range of critical speeds. The threshold values are in good agreement with the proposed theory. Contrary to the theoretical model, however, the measured wave resistance reveals a non-monotonic speed dependence after the threshold.