Isaac Newton And The Theory Of Gravity

Sir Isaac newton

The story of Sir Isaac Newton and the falling apple sparking his insight into the nature of Gravity  is a much loved and often retold anecdote. According to the myth, while Newton sat under an apple tree contemplating life, the universe and everything in general, he was hit in the head by an apple that fell from a tree. This supposedly led him to ponder why apples always fall straight to the ground rather than sideways or upwards. 

Newton’s contemplation of the falling apple prompted him to form the law of universal gravitation that proposed the same force causing the apple to fall, also governs the motion of the moon and the planets, thus linking terrestrial and celestial mechanics.

While this version of the apple story has been popularised over the years, there is no evidence that an apple actually hit Newton on the head. Instead, it is more likely that the sight of a falling apple simply prompted Newton to think deeply about gravity. 

The earliest accounts of this story come from Newton's contemporaries. The most detailed version is provided by William Stukeley, who wrote about it in his biography of Newton. Stukeley recounts a conversation with Newton in which Newton mentioned the apple incident. However this account wasn’t written until 1752, several decades after the event and well after Newtons death in 1727.

The story of Newton and the apple is a blend of historical fact and myth that highlights the importance of curiosity and observation in scientific discovery underscoring how a seemingly mundane event can lead to groundbreaking insights that change our understanding of the world.

However, even though the story may be  emblematic of the moment of scientific inspiration, it tends to over simplify  the complex process of Newton's discovery, and the many influences from previous discoveries by the great thinkers of the time. Newton has often been quoted as having written to fellow scientist and antagonist Robert Hooke “If I have seen further it is by standing on the shoulders of giants”. Though this quote is not original, it has become metaphorical in describing the progression of science built on previous work. 

And so it was for Newton and his theory of gravity. The apple may have sparked a thought process, but the process was backed up by Newton's knowledge of the great work that preceded him.

Johannes Kepler's laws of planetary motion, which describe the orbits of planets around the sun as ellipses rather than perfect circles, were crucial. Kepler's empirical laws were derived from the meticulous astronomical observations of Tycho Brahe. Newton's work provided a theoretical framework that explained why planets follow these elliptical paths.

Galileo Galilei's studies on motion and his experiments with falling bodies provided foundational insights into the acceleration of objects under gravity. He established that objects accelerate uniformly in the absence of air resistance, laying the groundwork for Newton's first law of motion and the concept of inertia.

Statue of Sir Isaac Newton - Oxford University

René Descartes'  emphasis on mathematical principles and rationalism helped shape the scientific approach Newton adopted even though Newton disagreed with Descartes' ideas about vortices driving planetary motion. 

Christiaan Huygens made significant contributions to the understanding of centrifugal force and the principles of mechanics. His work on pendulums and centripetal force directly influenced Newton's thinking about circular motion and gravity.

Even though Robert Hooke had a contentious and antagonistic relationship with Newton right up until Hooke’s death, his ideas about gravitational attraction were a significant precursor to Newton's work. Hooke proposed that bodies attract each other with a force that decreases with the square of the distance between them. He engaged in correspondence with Newton about planetary motion and gravitation, which helped spur Newton to develop his comprehensive theory. 

Isaac Barrow was Newton's mentor and predecessor as the Lucasian Professor of Mathematics at Cambridge. Barrow recognized Newton's genius and helped promote his early career. His teachings and works on geometry and optics provided a foundation for Newton's own studies. 

Newton synthesised these prior ideas and observations, integrating them into his universal law of gravitation. This law, articulated in his "Principia Mathematica," mathematically demonstrated that every mass attracts every other mass with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centres. This comprehensive framework unified terrestrial and celestial mechanics, transforming the understanding of the physical universe.

In Series 3 Episode 1 Kennardley finds out about the life of Sir Isaac Newton. Click below to listen.

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