This study has showned us the importance of the resonance effect. The system, subjected to an exciting force, can become instable when the frequency of this force reach a certain value, which is the resonace frequency. Therefore, it is very important to know the resonance frequency of the system, especially when the system is a way of transport (Plane, train, ...). In the example studied, one has considered that there was no friction forces and that the angles were weak, what is not true, especially near the resonance. However, even the phenomenon had been less important in reality, this phenomenon had happend. So it is realy important to avoid it, which allows the sytstem not to be hurt by excessive vibrations.