 Atoms can differ in size, shape, order and position; they move about in the void, and—depending on their shape—some can temporarily bond with one another by means of tiny hooks and barbs on their surfaces. Thus the shape of individual atoms affects the macroscopic texture of clusters of atoms, which may be fluid and yielding or firm and resistant, depending on the amount of void space between and the coalescence of the atomic shapes. The texture of surfaces and the relative density and fragility of different materials are also accounted for by the same means. Atoms cannot fuse, but rather repel one another when they collide. Observations about the tendencies of bodies bumping one another were frequently exploited to explain the apparently patterned motions of macroscopic bodies in the visible world.