Kapitza's pendulum is a rigid pendulum in which the pivot point vibrates in the vertical direction, up and down. It is named after Russian Nobel laureate physicist Pyotr Kapitza, who in 1951 developed a theory that successfully explains some of its unusual properties. The unique feature of the Kapitza pendulum is that the vibrating suspension can cause it to balance stably in an inverted position, with the bob above the suspension point.
 Wikipedia. "Kapitza's Pendulum." (May 20, 2019) en.wikipedia.org/wiki/Kapitza%27s_pendulum.