Newtonian potential function is used to represent polygonal objects and obstacles. The closed-form expression of this potential field and other gradient-related quantities are derived. Such results not only eliminate the problems associated with the discretization of the object and obstacles in evaluating the risk of collision, but also make the search for the optimal object configurations efficient. The object skeleton, a shape description of the moving object, is introduced to guide the moving object through narrow regions while the search is done at different stages. The free space can then be divided by the narrow regions where the path planning takes place--a very simple free space decomposition scheme. Successful global strategies are developed to connect the local plans into a safe and smooth global path.