Did Newton get the idea of the law of gravity, when, sitting under a tree, he was hit on the head by a falling apple?

Isaac Newton’s apple story

Sir Isaac Newton was born in Lincolnshire in east England on January 4, 1643. He was a mathematician, a physicist, an astronomer, and a theologian. He was one of the most famous researchers of his time and is regarded as one of the most influential scientists of all time.

In 1687 he came out with his book Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). In it, he used mathematic formulas to explain the motions of objects in space. He showed how to apply the same mathematical principles on various bodies on earth, he calculated trajectories of comets, the rise, and fall of the tide, and he formulated the Law of Gravity. He laid the foundation of Classical Mechanics.

Newton’s law of gravity

Newton’s law of gravity explained the force of attraction between two objects. He did not, however, discover gravity. The fact that bodies attract each other had been discussed among scientists before Newton. What Newton did was demonstrate the exactness of the inverse-square law of attraction through mathematical calculations.

This is how it works:

Every point mass attracts every single other point mass by a force acting along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between them.

Newton’s apple story

The Newton’s-apple story originates from when he was already a well-established scientist, and it exists in many versions. The occasion should have been when Newton, due to an outbreak of the Bubonic plague in 1666, had to leave Cambridge (where he was studying at Trinity College) and return to his mother’s house in Lincolnshire.

It’s obvious that Newton liked the story and told it often to entertain and amuse his friends. The fact that it contains a falling fruit that is round, explains very well the idea of attraction between bodies. The earth attracts the apple and the apple attracts the earth.

The Apple is also a mythical and religious symbol. As Newton had a very intimate relationship with the Holy Bible, he would use an object that refers to originality and maybe even wisdom… The forbidden fruit in Eden.

What we know is that Isaac Newton told the story to his friends, but we have no idea if it is true.

And Newton’s apple story never actually included an apple bonking him on the dome. He mostly told that he saw it falling. As in the book “Memoirs of Sir Isaac Newton” by William Stukeley…

After dinner, the weather being warm, we went into the garden, & drank tea under the shade of some apple trees… he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. Why should that apple always descend perpendicularly to the ground, thought he to himself; occasioned by the fall of an apple, as he sat in a contemplative mood

Newton’s law of gravity, was it really such a revolutionary discovery?

As mentioned before, it was probably not a Eureka experience. It was not like Isaac Newton is sitting under the tree and suddenly he understands that we don’t fall off the earth because there was such a thing as gravity. He was a scientist and he did scientific calculations about things around him.

When Newton’s book, Philosophiæ Naturalis Principia Mathematica (or “the Principia” in short), was published on July 5, 1687, Robert Hook, a fellow English scientist and member of the council at Royal Society, claimed that it was he who had given Newton the idea of the inverse-square law. But this is highly unlikely.

Surely the inverse-square law had been discussed. But not only with Hook. Newton acknowledged the works of quite a few other scientists in the foreword to the book.

Robert Hook was also known as a rather unpleasant man. Arthur Berry writes about him in his book, A short History of Astronomy “...Hooke claimed credit for most of the scientific discoveries of the time.”

Still, Newton’s principles of gravity were without parallels in science at the time. He became one of the most important scientists ever. And together with a few others like Einstein, Galilei, da Vince, Tesla, one of the most famous.

What remains is that it was Newton who mathematically described and explained the one single natural law that keeps us all together. The law of attraction between bodies.

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