  A set of hard spheres with tangential inelastic collision is found to
reproduce observations of real and numerical granular matter. After time is
scaled so as to cancel energy dissipation due to inelastic collisions out,
inelastically colliding hard spheres in two dimensional space come to have
$1/f^\alpha$ fluctuation of total energy, non-Gaussian distribution of
displacement vectors, and convective motion of spheres, which hard spheres with
elastic collision, a conventional model of granular matter, cannot reproduce.
