  Super hydrophobic surfaces have been the focus of research in the recent
years.One of the reasons for this is the self cleaning property of these
surfaces which emerges from the ability of the droplets to roll freely over
them.However majority of the studies available in literature are on the static
wetting behavior of liquid droplets on such surfaces and the physics of the
motion of droplets has not been studied exhaustively either theoretically or
experimentally.In the present study droplet motion on super hydrophobic
surfaces has been modeled to analyze the sliding/ rolling characteristics of
the droplet motion.A non-dimensional number is proposed to indicate whether a
given droplet would tend to roll or slide more on a given super hydrophobic
surface.We refer to this number as 'Slip Reynolds' number. Simulations of
droplet motion were carried out with different surface and droplet
characteristics leading to a unique value of this number corresponding to
sliding/rolling behavior.The applicability of this number was tested with
available experiments from literature.
