  Conditions are investigated under which a body lying at rest or rocking on a
solid horizontal surface can be removed from the surface by hydrodynamic forces
or instead continues rocking. The investigation is motivated by recent
observations on Martian dust movement as well as other small- and large-scale
applications. The nonlinear theory of fluid-body interaction here has unsteady
motion of an inviscid fluid interacting with a moving thin body. Various shapes
of body are addressed together with a range of initial conditions. The relevant
parameter space is found to be subtle as evolution and shape play substantial
roles coupled with scaled mass and gravity effects. Lift-off of the body from
the surface generally cannot occur without fluid flow but it can occur either
immediately or within a finite time once the fluid flow starts up: parameters
for this are found and comparisons are made with Martian observations.
