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Bodies and Media

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Abstract

This book presents a recasting of Aristotle’s theory of spatial displacement of inanimate objects. Aristotle’s claim that projectiles are actively carried by the media through which they move (such as air or water) is well known and has drawn the attention of commentators from ancient to modern times. What is lacking, however, is a systematic investigation of the consequences of his suggestion that the medium always acts as the direct instrument of locomotion, be it natural or forced, while original movers (e.g. stone throwers, catapults, bowstrings) act indirectly by impressing moving force into the medium. Filling this gap and guided by discussions in Aristotle’s Physics and On the Heavens, the present volume shows that Aristotle’s active medium enables his theory - in which force is proportional to speed - to account for a large class of phenomena that Newtonian dynamics - in which force is proportional to acceleration - accounts for through the concept of inertia. By applying Aristotle’s medium dynamics to projectile flight and to collisions that involve reversal of motion, the book provides detailed examples of the efficacy and coherence that the active medium gives to Aristotle’s discussions. The book is directed primarily to historians of ancient, medieval, and early modern science, to philosophers of science and to students of Aristotle’s natural philosophy.

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Up until the Industrial Revolution, the dynamic mechanical properties of materials were only of importance in warfare, particularly after the powder-driven gun was invented. With the invention of the steam engine, the explosion of steam boilers (which is similar to the explosion of cannon) became a concern. When railways began to be built, the lack of knowledge of the dynamic properties of the iron alloys used in rails and railway bridges was understood to be a problem, but no way of measuring them was devised until the end of the nineteenth century. Ingenious mechanical (and later electromechanical) methods of recording signals onto rotating drums or moving smoked glass plates began to be developed from the middle of the nineteenth century onwards. Optical/photographic methods of recording information from dynamic experiments date from the 1890s. The rod-on-anvil technique (later named after Taylor) was developed in France at the beginning of the twentieth century but not mathematically analysed until the 1940s. The Hopkinson pressure bar was invented just before the start of the First World War and found to be useful in improving British artillery shells. It was then forgotten about until the Second World War when a two-bar version was developed for measuring the dynamic properties of soft materials such as explosives and polyethylene. As the story of high rate mechanical testing from about 1950 onwards is quite well known to the high rate testing community, this date is taken as the end point of this article.
Chapter
Most of the time, improvements to armour, as in other areas of science and technology, are gradual. From time to time, however, substantial changes take place. What I have attempted to do in this chapter is (i) to identify these “step changes”, (ii) to give an impression of what was going on politically and militarily at the time that influenced technology and design, and (iii) to introduce the people involved.
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