This benchtop unit is used to show theresonance and critical bending speed on rotating shafts. The construction ofthe rotor of a thin, flexible shaft and rigid weights facilitates thetheoretical comprehension. The rotor is held on the base frame with pivotingbearings. The weights and bearings can be placed at any location along theshaft and attached securely with quick-acting clamps. It is driven by aflexible coupling. Two motor speeds can be fine-adjusted and preset with ten-speedpotentiometers. They are controlled electronically and displayed digitally. Itis possible to switch speeds during the experiment as desired. A transparentprotective hood covers the rotating parts. A set of electrical vibrationsensors with clamping set is also available.