I saw this demonstration at West Point Military Academy. The academy faculty wanted a closer integration of the differential equation math course with physics and engineering, so a mechanical engineering professor came to the math class to encourage the analysis of resonance and to encourage the study of mathematics by engineering majors. He described the problems that result when the blades of a helicopter are out of balance and the machine shakes itself apart. After seeing the demo, I had to have one.

When students observe the spinning bicycle wheel they are somewhat surprised when it starts bouncing up and down, but really surprised when it settles down again. The tube valve stem makes the center of mass of the wheel slightly off center with the axle. The resultant force does little until the resonance frequency of the wheel-spring system is approached as the wheel slows down. Of course, it passes through resonance with further slowing. It is clear to everyone in class that when the tire on their car loses a balance weight and they hit resonance, they can either slow down....or speed up.

This is a good demonstration of resonance for all classes, but may be especially good in classes where differential equations are treated: differential equations in math, mechanics in physics, and dynamics in engineering. Ask what drives the oscillation. It has to do with the center of mass not being on the axis of rotation.

Thanks to Mike Lucas and the machine shop for construction.

Resonance