Before Natural Acceleration

By way of introduction, the chapter considers aspects of Galileo’s considerations regarding motion and mechanics prior to his conceptual shift toward the assumption that motion of fall is naturally accelerated. The aspects discussed have been selected for the relevance they assumed when, from 1602 onward, Galileo started to engage in the investigations which eventually led to the establishment of his new science of motion. In particular, his understanding of the free fall of heavy bodies and of acceleration is being presented as it is reflected in a compilation of early manuscripts, which have come to be referred to as De Motu Antiquiora. One of these manuscripts, commonly designated as On Motion, contains a chapter in which Galileo investigated the dynamics of motion along inclined planes and, in particular, provided a proof for the law of the inclined plane relating the inclination of the plane to the force along this plane experienced by a body placed upon it. Galileo’s arguments in this chapter are discussed in some detail.