The Laws of Inertia and Gravitation in Newtonian Physics

Abstract

It seems appropriate to begin the historical analysis of the laws of inertia and gravitation with the work of Galileo. Of course, in the classical Greek period, in the Hellenistic period, and in the early middle ages, there was already much activity and also progress in the natural sciences and in ‘physics’, a term introduced by Aristotle in around 335 bc. However, in those days, arguments were mostly of a philosophical and qualitative character, and not corroborated by experiment. Moreover, it was more or less a dogma that the phenomena and laws of the cosmos were independent of, and indeed generally different from, those prevailing on Earth. If dynamical processes were analyzed at all, the aim was to find a cause (a ‘force’) for the velocity of an object, and not for its acceleration, as is the case in modern physics. In short, one can say that the Aristotelian philosophy, so dominant for many centuries, was more of a hindrance than a help in the search for the correct laws of inertia and gravitation. (For a detailed presentation of the classical and Hellenistic period, and of the middle ages, especially from the point of view of absolute versus relative concepts, see, e.g., Barbour 1989, Chaps. 2– 4)