A one dimensional lattice model is formulated to study tapping dynamics and
the long time steady distribution in granular media. The dynamics conserves the
number of particles in the system, and density changes are associated to the
creation and destruction of empty sites. The model is shown to be consistent
with Edwards thermodynamics theory of powders. The relationship with lattice
models in which the number of particles is not conserved is discussed.Comment: 18 pages in revtex preprint style, 4 figures; Phys. Rev. E (in press