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Chapter 2 - The pre-history of classical dynamics

Published online by Cambridge University Press:  05 December 2012

Lawrence Sklar
Affiliation:
University of Michigan, Ann Arbor
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Summary

Some Greek knowledge and speculation

The motion of the heavenly bodies, observed as lights in the sky, provides us with a remarkable spectacle of a phenomenon describable in a small number of terms and exhibiting an easily noted regularity in space and time. This spectacle caught the attention of many cultures in the beginnings of their attempts to characterize the world as a place of some describable order. Most of the cultures were unable to get beyond the ability to discover numerical formulae that allowed one to predict recurrences in the domain of the heavens, sometimes with astonishing accuracy. In ancient Greece, however, astronomy took science further. In particular, Greek astronomy involved deep connections with Greek attempts to construct a general dynamical theory of motion and its causes. This close connection between dynamics and astronomy persisted throughout the history of classical dynamics, as we shall see. It is necessary for us, therefore, to say a little bit about some of the aspects of Greek astronomy that impinged upon Greek theories of motion.

By the time of the Greek classical era, many important facts were well known and widely agreed to. Whereas early Greek speculation about the shape of the Earth thought of it as flat, perhaps a disk of land surrounded by a circumventing ocean, it was soon an accepted fact that the Earth had the form of a sphere. Observations on how the elevations of stars changed as one moved north or south, how ships disappeared a little at a time over the horizon and how the length of a day varied with latitude could be explained only by invoking such a shape for the Earth. By analogy, models of the Moon and Sun as illuminated disks were soon replaced by accounts of these heavenly bodies as also spherical. (It is remarkable how spherical the Moon looks, in fact, when seen during a total eclipse.)

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Publisher: Cambridge University Press
Print publication year: 2012

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