Isaac Newton (1642–1727) was a polymath who made vital contributions across an array of scientific disciplines. However, it was his formulation of the laws of motion and the theory of gravity that established him at the very forefront of the pantheon of history’s greatest scientists.
Among Newton’s multitude of achievements, he played an important role in the development of telescopic lenses, infinitesimal calculus and even alchemy, to name but a few. But his magnum opus was Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), published in 1687.
Newton’s three laws of motion
In his Philosophiæ Naturalis Principia Mathematica Newton elucidated his three laws of motion, so becoming the first to account comprehensively for the movement of objects through space using theoretical mathematics:
The law of inertia: ‘An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.’
The second law says that acceleration is produced when a force acts on a mass. The larger the mass, the larger the force required to accelerate it.
The third law says that ‘for every action, there is an equal but opposite reaction’.
In the same work, Newton also detailed his theory of universal gravitation – the notion that all things are attracted to all other things in space by means of an invisible force. It is famously said that the idea of a universal force of attraction came to him as he sat under a tree and an apple fell on his head. Inspired, he was prompted to ask why the apple should always take that course and not for instance fly off upwards or sideways. Whatever the theory’s origins, it was instrumental to his laying the foundations of classical mechanics. Not only did he provide mathematical proof of the veracity of the heliocentric model (see here); he essentially explained for the first time why things move as they do – on Earth and in the heavens.
Newton Under the Tree
Newton made good use of the planetary observations of Joseph Kepler in formulating his theories. Nonetheless, most would concede that Newton was a giant in his own right, revealing more about the workings of the universe than anyone before him.
Newton’s ideas went unchallenged for three centuries. Einstein himself acknowledged the unique position Newton holds in the history of human understanding, writing in 1952: ‘Newton’s discoveries have passed into the stock of accepted knowledge.’