Active Shock Absorbers
Active shock absorbers are used in several kinds of machines and vehicles (for example, in a seat, as shown in the graphic). An active shock absorber is basically a damped harmonic oscillator with spring constant for a mass . This technology uses magnetorheological fluids that change their damping factor when a magnetic field is applied. Three different damping functions are considered here.
The equation for the system is , where can be chosen according to the application.
 P. Blanchard, R. L. Devaney, and G. R. Hall, Differential Equations, 4th ed., Boston: Brooks/Cole, 2012 pp. 454–456.
 G. Stix, "Project Skyhook," Scientific American, 284(5) pp. 28–29.
 Wikipedia. "Magnetorheological Fluid." (Jan 15, 2012) en.wikipedia.org/wiki/Magnetorheological_fluid.