(Or equilibrium paraboloid.) The geometrical figure obtained by rotating a parabola about its axis. In experimental meteorology and oceanography such a figure is sometimes used as the lower boundary of a model atmosphere or ocean, and is especially important because, at a proper rotation rate, it is an equipotential surface for apparent gravity in the model. If ω is the rotation rate of the apparatus, the acceleration of local earth's gravity, the coordinate parallel to the vertical rotation axis, and the radial coordinate, an equilibrium paraboloid is given by This surface is the laboratory equivalent of the spheroidal equipotential surfaces of the earth's apparent gravity field.