Many mechanisms use Hertzian contacts. During operation, these contacts are generally excited by a dynamic normal load. To study the non-linear vibrations of a sphere-plane contact we have built a device which uses a symmetrical plane-sphere-plane contact. The first step was to study free vibrations under a static normal load. Our elastic system can be summarized as a one-degree-of-freedom non-linear oscillator. Numerical and analytical methods were used to predict the main properties of the dynamic response (contact natural frequency, frequency contents, softening behaviour). A first set of experiments, on free contact vibrations, has shown that the measured contact natural frequency is in very good agreement with the theory, and that in dry contacts the contact damping is small and can be reasonably described by an equivalent viscous damping. In lubricated contacts, a fluid pumping mechanism can add a noticeable amount of damping. A second set of experiments on forced contact vibrations was performed in order to study dynamic contact load during the principal non-linear resonance. A softening dynamic behaviour is observed and the level of the dynamic contact load can be greater than twice the static load just before the jump observed during a scan of decreasing frequency.