¥Packed, frictionless particles are solid, but qualitatively different from elastic solids.
¥Distinctive features can be explained by a single property: isostaticity
–ray-like force propagation
–marginal vibrational modes
¥randomized square lattice reproduces properties of particle packs
–details of the packing process seem unimportant
¥How are particle packs distinct from general isostatic networks?
–eg. reconnection of network from stress