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Abstract: Mechanical milling (MM) is referred to a solid state size reduction process where work materials in the form of coarse particulates are broken into the ultimate fineness by means of mechanical impact created by collisions of the work materials and the milling media which are placed inside a reciprocating vial. Many milling techniques have been so far developed to improve the process. However, the efficiency of MM process is still below satisfactory in terms of energy balance, where the energy consumed by the process of reduction is still very low compared to the energy supplied to perform the milling process itself. This contributes to high energy losses and proportionally to the span of processing time. Other major problems inherent in the process are contamination by the balls and the vial materials into the work materials, and process temperature that could influence the properties of milled materials. Since MM process utilizes the energy generated by impact upon the collisions of the balls against the work materials, it is important to understand the motions of the balls, the work materials, and the vial, which are the sources of the generation of impact energy. To obtain an optimized processing condition, the motions of vial and ball in relationship with the work materials should be designed in such a way to ensure the optimum impact energy is consumed by the work materials for the size reduction purposes. This paper presents a physical model for work materials, balls, and vial collisions based on different ways of motions. Using this model, higher impact could be achieved. These would lead to the reduction of milling time, contamination, as well as milling temperature. [Copyright &y& Elsevier]