The interaction force acting on an individual micrometer-size polystyrene particle near a flat, electrically conducting substrate has been measured by attaching the particle to an atomic force microscope cantilever. From the spatial dependence of the interaction force, the equations of motion governing a particle near the substrate can be determined. These considerations allow a prediction of the jump-to-contact distance of the particle as it approaches the substrate. This distance is measured as a function of particle radius and compared with predictions bused on the relevant interaction force models.