Boltzmann Equation: A Gas of Grains

A simple but realistic and rich model for fluidized granular media is the gas of inelastic hard spheres. In this chapter its statistical description is reviewed. A key role is played by the assumption of Molecular-Chaos and by the Boltzmann equation. A comparison with the case of elastic hard spheres is made, pointing out the analogies and the differences. The chapter is concluded with the discussion of the protocols used for energy injection.