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<sub>p</sub>). It is generally believed that a low Re<sub>p</sub> 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.