The vibrations excited by a rotating mass at the end of a cantilever beam are studied experimentally at the two universities given above. The mass is connected to the shaft of a DC motor with limited power. The response to changes in the applied voltage near resonance differs markedly from the response away from resonance: away from resonance, changes in the voltage applied to the motor are nearly linearly related to changes in the speed of the shaft and the amplitude of the motion remains small; near resonance changes in the voltage produce changes in the amplitude of the motion but have little or no effect on the speed of the shaft. Consequently, if the voltage is limited, it may not be possible to accelerate the motor-structure system through resonance. The Sommerfeld effect was observed, and it was found the jump associated with it could be extended by increasing the mass; however, the power needed to pass through resonance increased as the unbalanced mass increased. Regions of significantly modulated motions were found.