Dynamical System
Dynamics, the branch of science which studies systems in motion, particularly planetary motion, has been a source of fascination since the beginning of history.
The first planetary laws of motion were drawn up by the Greek philosopher Aristotle around the fourth century b.c. Among the three laws of motion Aristotle recognized, were natural motion, forced motion, and voluntary motion. Aristotle further believed that all the celestial bodies moved in circles around the Earth. While this is now known to be false, most of Aristotle's theories were accepted without question up until the fourteenth century. At that time, Polish astronomer Nicholas Copernicus published his theories substantiating the notion of a stationary Sun, surrounded by orbiting planets. However, Copernican views were met with great opposition, both from the Roman Catholic church as well as the scientific community. With no knowledge of the laws of gravity, scientists believed people and buildings on the Earth's surface would fall off into space if the Earth was truly rotating. Nevertheless, the Copernican theory initiated a new age of astronomy, in which mathematical measurements and calculations became increasing relied upon over mystical and religious concepts.
In 1618 the German astronomer Johannes Kepler released his three landmark laws of planetary motion. The first two laws showed that planetary orbits were actually elliptical (oval), rather than circular in shape. Additionally, he offered that the planets traveled at nonuniform rates around the Sun, although Kepler remained puzzled over the force that maintained the orbit of planets.
About the same time as Kepler, the Italian astronomer Galileo also searched the stars, aided by the discovery of the telescope. Galileo definitively proved the Copernican concept and argued the theory that all bodies take the same time to fall to the ground from a given point, regardless of weight. Whether or not the story is historically accurate, he reportedly reached this conclusion by dropping different weights from the top of the Leaning Tower of Pisa. In his book Discourses on Two New Sciences, published in 1638, Galileo came close to discovering what is now known as Newton's first law of motion.
In 1644 René Descartes' Principles of Philosophy, which contributed to the world's knowledge of the laws of motion. Descartes claimed that a body will continue in motion at a fixed velocity in the same direction indefinitely, unless it has a collision. This came to be known as the law of inertia and served to influence the upcoming work of Isaac Newton.
Newton, while an eccentric genius, was without a doubt one of the greatest scientists to have ever lived. Newton's theories of dynamics (laws of motion) had a profound effect on the world of science, particularly with the realization that the physical laws of the Earth were the same as the laws of the planets.
In 1687 Newton published The Mathematical Principals of Natural Philosophy, a valuable book which presented Newton 's now famous laws of motion. Newton's first law states that a body will continue in a state of rest or uniform motion in a straight line unless acted upon by outside forces. His second law maintains that the change in motion will be proportional to and in the direction of the outside force. His third law asserts that to every action there is always an equal and opposite reaction. In the remainder of the book, Newton demonstrates the application of these laws both to the motion of bodies on Earth and to planetary bodies.
Newton's laws proved to be of monumental importance in several areas of science, resolving many of the problems and theories which had puzzled scientists and astronomers for centuries. Today, Newton's laws have been refined and developed to the point that we can send an unmanned spacecraft past a moon of Neptune, some 5 billion kilometers (3 billion miles) away, with bulls-eye precision, and astronomers have begun to explore, with powerful computers, the evolution of complex dynamical systems such as open and globular star clusters or even an entire galaxy.
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