ABSTRACT
A granular material that contains only even circuits of grains in contact makes up a novel state of matter, a dry fluid. It is a non-viscous fluid that does not resist shear, whose constituents roll without slip on each other or on any boundary or inclusion (the point of contact between any two grains has zero velocity, even though it changes all the time). It only feels hydrostatic pressure, i.e. forces normal to any plane inside the material on any scale larger than a few grains; a solid inclusion is subject to Archimedean pull only; arches can buckle freely and make ripples on free boundaries. The packing is bichromatic: every red grain has only blue neighbors, consistently throughout. Examples of dry fluids are aerated sand (Lohse et al. 2004), and numerical space-filling bearings (MahmoodiBaram & Herrmann, 2004).
