  We determine the most general form of the covariant drag force exerted on a
quark moving through a fluid dynamical flow. Up to first order in derivative
expansion, our general formula requires the specification of seven coefficient
functions. We use the perturbative method introduced in arXiv:1202.2737 and
find all these coefficients in the hydrodynamic regime of a $\mathcal{N}=4$ SYM
plasma. Having this general formula, we can obtain the rate of the energy and
momentum loss of a quark, namely the drag force, in a general flow. This result
makes it possible to perturbatively study the motion of heavy quarks moving
through the Bjorken flow up to first order in derivative expansion.
