  Experiments quantifying the rotational and translational motion of particles
in a dense, driven, 2D granular gas floating on an air table reveal that
kinetic energy is divided equally between the two translational and one
rotational degrees of freedom. This equipartition persists when the particle
properties, confining pressure, packing density, or spatial ordering are
changed. While the translational velocity distributions are the same for both
large and small particles, the angular velocity distributions scale with the
particle radius. The probability distributions of all particle velocities have
approximately exponential tails. Additionally, we find that the system can be
described with a granular Boyle's Law with a van der Waals-like equation of
state. These results demonstrate ways in which conventional statistical
mechanics can unexpectedly apply to non-equilibrium systems.
