Principia Mathematica

In 1679, Newton resumed his work on mechanics, i.e., gravitation and its consequence on the orbits of celestial bodies. He computed the attestation that the elliptical nature of the orbits would be the outcome of a centripetal force. This finding was published in a tract known as De motu corporum in gyrum and sent to the Royal Society and Edmond Halley, his long-time friend and fellow scientist. The tract was later expanded to form the Principia (Newton, 1729, pp. 10), and published in 1687.

In this book, Newton expressed the three laws of motion that were not altered for more than two centuries. The laws illustrate the relationship between the forces operating on a body and its motion. These were as follows:

1. 1st Law: “Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it” (NASA, 2010, para. 1).
2. 2nd Law: “Force is equal to the change in momentum (mV) per change in time. For a constant mass, force equals mass times acceleration” (NASA, 2010, para. 2).
3. 3rd Law: “For every action, there is an equal and opposite reaction” (NASA, 2010, para. 3).

Apart from the three laws, Newton gave a calculus-like formula for the geometrical computation by “first and last ratios”, presented the first analytical method for calculating the speed of sound, deduced the oblateness of the spheroidal shape of the Earth. He also justified the order of the equinoxes, began the gravitational study of non-uniformity in moon’s motion and gave a theory for obtaining the orbits of comets, among others. The Principia was the most important of Newton’s works and made him known internationally. He also acquired many friends, among them royalties, mathematicians, and scientists.