  As a first step to a more complete understanding of the local physical
processes which determine star formation rates (SFRs) in the interstellar
medium (ISM), we have performed controlled numerical experiments consisting of
hydrodynamical simulations of a kilo-parsec scale, periodic, highly supersonic
and "turbulent" three-dimensional flow. Using simple but physically motivated
recipes for identifying star forming regions, we convert gas into stars which
we follow self-consistently as they impact their surroundings through
supernovae and stellar winds. We investigate how various processes (turbulence,
radiative cooling, self-gravity, and supernovae feedback) structure the ISM,
determine its energetics, and consequently affect its SFR. We find that the
one-point statistical measurement captured by the probability density function
(PDF) is sensitive to the simulated physics. Aside from its effect on the
density structure of the medium, including self-gravity and/or supernovae
feedback changes the dynamics of the medium by halting the decay of the kinetic
energy. Since we find that the SFR depends most strongly on the underlying
velocity field, the SFR declines in the runs lacking a means to sustain the
kinetic energy, and the subsequent high density constrasts. This strong
dependence on the gas velocity dispersion is in agreement with Silk's formula
for the SFR (Silk 2001) which also takes the hot gas porosity, and the average
gas density as important parameters. Measuring the porosity of the hot gas for
the runs with supernovae feedback, we compare Silk's model for the SFR to our
measured SFR and find agreement to better than a factor two.
