  We use holographic duality to analyze the drag force on, and consequent
energy loss of, a heavy quark moving through a strongly coupled conformal fluid
with non-vanishing gradients in its velocity and temperature. We derive the
general expression for the drag force to first order in the fluid gradients.
Using this general expression, we show that a quark that is instantaneously at
rest, relative to the fluid, in a fluid whose velocity is changing with time
feels a nonzero force. And, we show that for a quark that is moving
ultra-relativistically, the first order gradient "corrections" become larger
than the zeroth order drag force, suggesting that the gradient expansion may be
unreliable in this regime. We illustrate the importance of the fluid gradients
for heavy quark energy loss by considering a fluid with one-dimensional boost
invariant Bjorken expansion as well as the strongly coupled plasma created by
colliding sheets of energy.

High Energy Physics - Theory;High Energy Physics - Phenomenology;Nuclear Theory