Journal of Physical Chemistry A, Vol.105, No.11, 2410-2413, 2001
A mechanical analogue of monotropism: Ordering of an ensemble of hemispheres
An ensemble of randomly oriented, noninteracting, homogeneous, solid, inelastic, identical hemispheres in the gravitational field, having dropped on a rigid horizontal plane will order orientationally, most of them sitting on the vertex of the spherical part rather than on the plane. This state of the ensemble will not have the lowest possible potential energy, as required for stable equilibrium. This shows several analogies to the behavior of polymorphic substances on crystallization from a gaseous or liquid phase, which usually first result in the highest energy solid. The discussion is extended to spherical segments (limited by a single plane) other than hemispheres. If mutual attraction is present, multiple metastable and stable states of the ensemble become possible, featuring positional besides orientational order.