Impetus

Abstract

In the Latin West, the concept of impetus was fully developed in the fourteenth century. John Buridan was the first to use this term in order to describe the projectile motion, the free fall, and the motion of the heavenly spheres. The discussion started with Aristotelian theory of projectile motion presented in his Physics. Aristotle claims that each violent motion, such as projectile one and freely falling body, need a constant presence of a mover, and therefore when a mobile is no more in touch with its mover, a medium takes its role. Later, Greek and Arabic commentators of Aristotle noticed that a medium resists rather than promotes motion. Thus, they offer an alternative theory, that a mobile is moved thanks to a force impressed by the mover. This theory was developed in the Middle Ages, and finally it became a kind of an “official” technical concept of medieval mechanics. The medieval different concepts of impetus finally lead to formulate proper definitions of violent and natural motions and to replace the whole Aristotelian system. Although ontologically different, impetus is analogous to Galileo’s early use of impeto and Newton’s “quantity of motion.”