This paper investigates the underdamped motion of a bead as it moves toward the focal
point of an optical trap. The model used herein represents a new approach toward addressing
singular perturbation problems in dynamics. The experiments involve trapping microbeads
at the focal point of an optical tweezer/trap. The optical trap can accurately measure
the position of a microbead only in two directions. Given experimental data, the model
can be used to estimate the bead's position in the third direction. This estimate
allows an examination of the full position, velocity and acceleration of the bead,
which in turn allows and investigation of its particle Reynolds number (Re-p). It
is generally believed that a low Rep implies that a small bead will exhibit overdamped
motion. The velocity estimates obtained herein for three bead diameters, 1950nm, 990nm
and 500nm, provide new insights into the interpretation of a low Rep in light of the
underdamped motion observed in experiments.
