 Physics VII.5 (249b27–250b10) discusses some problems of simple mechanics (Lettinck 1994: 559–561). The moving-agent is always moving something in a certain time and a certain distance, and Aristotle presumes here that motion here is at a constant velocity. There is a relationship between the four factors, for instance if A sets B in motion over a distance C in time D, A will move half B over the distance C in half the time D, because there is a proportion between the force of A and the load of B. Aristotle sees limits to the interchange because “it may well happen that it [a fraction of A] cannot move B at all” (250a15–16). Thirty men can tow a ship over a distance and in a time, but one man cannot tow it either over any distance or in any time. He also faces Zeno’s contention that every grain of millet must make a sound when it falls as the whole measure does stirring the air and answers that the grain is part of a whole and that the whole is the moving-agent.