  Understanding the survival, growth and dynamics of cold gas is fundamental to
galaxy formation. While there has been a plethora of work on `wind tunnel'
simulations that study such cold gas in winds, the infall of this gas under
gravity is at least equally important, and fundamentally different since cold
gas can never entrain. Instead, velocity shear increases and remains
unrelenting. If these clouds are growing, they can experience a drag force due
to the accretion of low momentum gas, which dominates over ram pressure drag.
This leads to sub-virial terminal velocities, in line with observations. We
develop simple analytic theory and predictions based on turbulent radiative
mixing layers. We test these scalings in 3D hydrodynamic simulations, both for
an artificial constant background, as well as a more realistic stratified
background. We find that the survival criterion for infalling gas is more
stringent than in a wind, requiring that clouds grow faster than they are
destroyed ($t_{\rm grow} < 4\,t_{\rm cc} $). This can be translated to a
critical pressure, which for Milky Way like conditions is $P \sim 3000 {\rm
k}_B {\rm K}\,{\rm cm}^{-3}$ . Cold gas which forms via linear thermal
instability ($t_{\rm cool}/t_{\rm ff} < 1$) in planar geometry meets the
survival threshold. In stratified environments, larger clouds need only survive
infall until cooling becomes effective. We discuss applications to high
velocity clouds and filaments in galaxy clusters.
