Static equilibrium margin for cylinder cone and frustum of a cone

The difference of equilibrium features of cylinder, cone and frustum of a cone statically placed on a plane, is analyzed. A new concept of equilibrium margin for quantitative describing the equilibrium state of static systems is put forward, and the definition formulas of equilibrium margin for cylinder, cone and frustum of a cone are proposed by means of potential energy criterion for objects at static equilibrium in the gravitational field, the influences of the variations of geometric dimensions for an object on the margin are discussed in detail. A new method to system risk evaluation is also provided with the aid of the concept of equilibrium margin.