English: Diagram of a Kapitza pendulum, a rigid pendulum with a vibrating suspension point, used as an example of a parametric oscillator with "dynamic stabilization" in control system theory. This device was first analyzed in 1951 by Russian Nobel laureate physicist Pyotr Kapitza. It's unique feature is that the vibrating suspension can cause the pendulum to balance stably in an inverted position, with the bob over the pivot. In an ordinary pendulum with a fixed pivot, the only stable equilibrium point is the pendulum hanging down below the pivot; the inverted position is a point of unstable equilibrium and the slightest disturbing force causes the pendulum to move away from the point. The drawing shows how a Kapitza pendulum can be constructed, with a motor that turns a crank at a high speed (4000-6000 RPM), the crank vibrates a lever arm up and down, one end is fixed and the other end supports the pendulum by a pivot. If the pendulum is released with the bob near vertical, the bob will oscillate back and forth about the vertical until the oscillations damp out, leaving it standing upright