On July 6th: 325th Anniversary of Newton's 'Principia'

The above image shows the cover page of the first edition (1687) of Philosophiæ Naturalis Principia Mathematica. Image Credit: The image is in the Public Domain.

Today is the 325th anniversary (July 5th, 1687) of the publication of Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) by Sir Isaac Newton. In the pursuit of brevity we have come to reference the work simply as Newton's Principia. The three-volume work has been described as one of the most important in the history of science. The Principia states Newton's laws of motion, which form the foundation of classical mechanics, also Newton's law of universal gravitation, and a derivation of Kepler's laws of planetary motion.

In a nutshell, Newton's laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces. They have been expressed in several different ways over nearly three centuries, and can be summarized as follows:

1. First law: Every object continues in its state of rest, or of uniform motion in a straight line, unless compelled to change that state by external forces acted upon it.

2. Second law: The acceleration a of a body is parallel and directly proportional to the net force F acting on the body, is in the direction of the net force, and is inversely proportional to the mass m of the body, i.e., F = ma.

3. Third law: When two bodies interact by exerting force on each other, these action and reaction forces are equal in magnitude, but opposite in direction.

Newton used his laws to explain and investigate the motion of many physical objects and systems. For example, Newton showed that these laws of motion, combined with his law of universal gravitation, explained Kepler's laws of planetary motion.

In honor of Sir Isaac Newton, the European Space Agency (ESA) renamed an Earth-orbiting X-ray observatory mission for him. Specifically, the X-ray Multi-Mirror Mission - Newton (XMM-Newton), which launched December 1999. To learn more about the XMM-Newton, visit these URLs: xmm.esac.esa.int and xmm.sonoma.edu .

Several copies of Newton's Principia are available online for your reading pleasure. Here is one such copy which is available in several file formats at the Internet Archive: rchive.org/details/newtonspmathema00newtrich .

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