1. Let's say we have a large, charged sphere in aqueous NaCl solution (this sphere is large enough to sediment in the field of gravity - say, 10m diameter). This sphere is in a vessel made up of the same material as the sphere, and the vessel carries like charges. As this sphere approaches the bottom of the vessel (we shall approximate as flat), electrostatic repulsion will prevent the sphere from settling completely. Instead, our large sphere will hover at a distance Zmin above the glass, which corresponds to where the minimum in the potential curve for that sphere near the bottom - that is, by a superposition of gravitational energy and electrostatic repulsion energyas sketched in the figure below.