We present a general computational method of determining radiation pressure forces and torques exerted on small particles by a converging beam of light. This method, based on a ray optics model of optical trapping, allows time-series dynamic motion analysis to be performed on nonspherical objects that are initially positioned off the optical axis with arbitrary orientation. Comparison tests of computer simulation with experimental results prove that the proposed model can be used to predict complicated trapping behavior of microfabricated objects.