  The duality of gravitational dynamics (projected on a null hypersurface) and
of fluid dynamics is investigated for the scalar tensor (ST) theory of gravity.
The description of ST gravity, in both Einstein and Jordan frames, is analyzed
from fluid-gravity viewpoint. In the Einstein frame the dynamical equation for
the metric leads to the Damour-Navier-Stokes (DNS) equation with an external
forcing term, coming from the scalar field in ST gravity. In the Jordan frame
the situation is more subtle. We observe that finding the DNS equation in this
frame can lead to two pictures. In one picture, the usual DNS equation is
modified by a Coriolis-like force term, which originates completely from the
presence of a non-minimally coupled scalar field ($\phi$) on the gravity side.
Moreover, the identified fluid variables are no longer conformally equivalent
with those in the Einstein frame. However, this picture is consistent with the
saturation of Kovtun-Son-Starinets (KSS) bound. In the other picture, we find
the standard DNS equation (i.e. without the Coriolis-like force), with the
fluid variables conformally equivalent with those in Einstein frame. But, the
second picture, may not agree with the KSS bound for some values of $\phi$. We
conclude by rewriting the Raychaudhuri equation and the tidal force equation in
terms of the relevant parameters to demonstrate how the expansion scalar and
the shear-tensor evolve in the spacetime. Although, the area law of entropy is
broken in ST gravity, we show that the rewritten form of Raychaudhuri's
equation correctly results in the generalized second law of black hole
thermodynamics.
