Isaac Newton :

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One of the major scientific works which have contributed to a great leap forward in our understanding of the world is Isaac Newton's Philosophiae Naturalis Principia Mathematica. Written about 300 years ago and published in 1687, most of the ideas and laws it presents are valid today unlike many other theories of similar vintage. Given the norm of constant change in scientific understanding, the enduring relevance of this work is even more outstanding.


The Principia contains the essence of what is known as Newtonian or classical mechanics (summarised in Newton's three laws of motion), the demonstration that the force law for elliptical motion is inverse-square in nature and the universality of the law of gravitation (applying not just to the motion of planets and other heavenly bodies but also to objects on earth).

Since then it has been shown that Newton's laws of motion do not apply to atomic or nuclear domains nor to objects that are moving close to the speed of light. However, they explain the behaviour of everything else including the thrust of a jet engine, the paths of comets, how to hit tennis balls and the working of musical instruments.

The story of the apple falling down has been repeated so often that there have been suspicions that it may not be true. However Newton himself talked about the event in his old age to his friend, Dr.William Stukeley. This description invites us to understand how the great scientist thought through his ideas. After an apple had fallen to the ground, Newton thought to himself about the reason for it falling perpendicularly to the ground. He wondered why it does not fall sideways or upwards, but always towards the centre of the earth. He concluded that the earth must be drawing it to itself. A further induction was that matter in general contained the power to draw other objects to itself. The source of this power lies in the centre of the earth and not on any side of it. This would explain why the apple falls perpendicularly, or towards the centre.

Furthermore Newton surmised that if matter attracts other matter, the power acts in proportion to the quantity of matter present. So even as the earth pulls on the apple, so the apple pulls on the earth. In conclusion, the idea of the power called gravity can be extended across the universe.

Slowly, Newton applied this idea to the motion of the earth and other bodies in space. He found that gravity does explain how the planets maintained their orbits and did not crash into one another or even towards a paint in the universe. Thus Isaac Newton explained the workings of the bodies in space as well as those on earth.

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