We advance a quantitative description of the critical shear rate γc˙ needed to dislodge a spherical particle resting on a surface with a model asperity in laminar and turbulent fluid flows. We have built a cone-plane experimental apparatus which enables measurement of γc˙
Nearby in the stack
over a wide range of particle Reynolds number
Rep
from
10−3
to
1.5×103
. The condition to dislodge the particle is found to be consistent with the torque balance condition, which yields a lower
γc˙
compared with force balance because of the torque component due to drag about the particle center. The data for
Rep<0.5
is in good agreement with analytical calculations of the drag and lift coefficients in the
Rep→0
limit. For higher
Rep
, where analytical results are unavailable, the hydrodynamic coefficients are found to approach a constant for
Rep>1000
. We show that a linear combination of the hydrodynamic coefficients found in the viscous and inertial limits can describe the observed
γc˙
as a function of the particle and fluid properties.