This paper investigates the underdamped motion of a bead as it moves toward the focal point of an opticaltrap. The model used herein represents a new approach toward addressing singular perturbation problems indynamics. The experiments involve trapping microbeads at the focal point of an optical tweezer/trap. Theoptical trap can accurately measure the position of a microbead only in two directions. Given experimentaldata, the model can be used to estimate the bead’s position in the third direction. This estimate allows anexamination of the full position, velocity and acceleration of the bead, which in turn allows and investigation ofits particle Reynolds number (Rep). It is generally believed that a low Rep implies that a small bead will exhibitoverdamped motion. The velocity estimates obtained herein for three bead diameters, 1950nm, 990nm and500nm, provide new insights into the interpretation of a low Rep in light of the underdamped motion observedin experiments.
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