  The force network ensemble is one of the most promising statistical
descriptions of granular media, with an entropy accounting for all force
configurations at mechanical equilibrium consistent with some external stress.
It is possible to define a temperature-like parameter, the angoricity
{\alpha}^{-1}, which under isotropic compression is a scalar variable. This
ensemble is frequently studied on whole packings of grains; however, previous
works have shown that spatial correlations can be neglected in many cases,
opening the door to studies on a single grain. Our work develops a Monte Carlo
method to sample the force ensemble on a single grain at constant angoricity on
two and three-dimensional mono-disperse granular systems, both with or without
static friction. The results show that, despite the steric exclusions and the
constrictions of Coulomb's limit and repulsive normal forces, the pressure per
grain always show a gamma distribution with scale parameter {\nu} =
{\alpha}^{-1} and shape parameter k close to k', the number of degrees of
freedom in the system. Moreover, the average pressure per grain fulfills an
equipartition theorem <p>=k'{\alpha}^{-1} in all cases (in close parallelism
with the one for an ideal gas). These results suggest the existence of k'
independent random variables (i.e. elementary forces) with identical
exponential distributions as the basic elements for describing the force
network ensemble at low angoricities under isotropic compression, in analogy
with the volume ensemble of granular materials.
