  The drag forces acting on a single polystyrene sphere in the vicinity of an
oscillating glass plate have been measured using an optical tweezer. The phase
of the sphere is found to be a sensitive probe of the dynamics of the sphere.
The evolution of the phase from an inertially-coupled regime to a purely
velocity-coupled regime is explored. Moreover, the frequency dependent response
is found to be characteristic of a damped oscillator with an effective inertia
which is several orders of magnitude greater than that of the particle.
