Isaac Newton was born on January 4, 1643, at Woolsthorpe Manor House in the United Kingdom. Newton became a mathematician, physicist and astronomer and is now famous as a scientist who helped us understand the universe through his discoveries that became the basis of many scientific principles.

Newton published his ideas in three famous volumes which together are entitled The *Philosophae Naturalis Principia Mathematica* (Mathematical principles of natural philosophy), often referred to simply as *Principia*, which is, in all respects, a masterpiece. In this paper, Newton states his *three laws of motion*, which today forms the foundation of classical celestial mechanics. *Principia* it also exposes Newton’s revelations about gravity.

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**The three laws of Newton’s motion.** They are called *the laws*, but they are indeed descriptions of the fundamental truths about our physical universe.

1. An object at rest will remain at rest if it is not actuated by an external force. A moving object continues to move at the same speed and in the same direction, unless it is actuated by an external force. This law is often called *the law of inertia*. Click here to read more about Newton’s first law of motion.

2. When a force acts on a mass, *acceleration* is produced. The greater the mass of the object being accelerated, the greater the amount of force required to accelerate the object. Click here to read more about Newton’s second law of motion.

3. For each action there is an equal and opposite reaction. Click here to read more about Newton’s third law of motion.

**Newton’s revelations about gravity.** Remember the story of the apple falling on Newton’s head? Although not necessarily true in all its details, Newton apparently noticed that an apple was falling from a tree and began to think that in order to fall to the ground, the apple was *accelerated* from scratch when hanging from the tree.

According to its second law of motion, acceleration is produced when a force acts on an object. Newton must have thought, what is that force? He came to understand this force as what every school child today knows *gravity*.

Newton’s great revelation was that the gravitational force does not extend only to the tops of the seas. If an apple were as tall as a mountain, for example, the apple would still fall. The force would still work. Newton’s understanding was that the gravitational force extends much further … to the moon. He recognized that the moon’s orbit around the Earth is a consequence of gravitational force.

Indeed, the gravitational force extends throughout space. Today, physicists refer to Newton’s ideas about gravity as the universal law of gravity.

Others who followed Newton – especially Albert Einstein – refined our understanding of gravity. The most accurate description of gravity today can be found in Einstein’s general theory of relativity, which states that *gravity is a consequence of the space-time curve*.

Fascinated by Newton’s revelations about gravity? Watch this 15-minute video:

If Newton had contributed only the three laws of motion and the understanding of universal gravity, we would have remembered him as one of the greatest scientists in the world. But Newton didn’t stop here. He also built one of the first practical reflecting telescopes, helped invent calculus, and explored how white light can be divided into a spectrum of colors through a prism, laying the groundwork for much of modern astronomy. .

However, Newton himself knew how much remained to be discovered. He is known to have said:

I don’t know what can happen to the world, but to me it’s like I was just like a boy playing on the shore of the sea and wandering from time to time finding a finer pebble or a more beautiful shell than usual, while the great ocean of the truth lay undiscovered before me.

A curious fact about Isaac Newton is that you can say that he had two birthdays, ten days apart. You may have seen Newton’s birthday on December 25, 1642. This reference is beginning to change, and it is now more common to see Newton’s birthday on January 4, 1643. The difference is that when he was born, Newton, England was in the middle of a 150-year period of using a different calendar than the rest of Europe. The rest of the continent had already adopted the Gregorian calendar, which is the same calendar we use today. However, at the time of Newton’s birth, the English were still using the Julian calendar, which remained ten days ago, due to a faulty method of accounting for leap years. (Coincidentally, 1642 was the year Galileo died.)

So Newton himself would have said that his birthday would be December 25th. But anywhere outside England he was born on January 4th. Read more about Newton’s birthday discrepancy.

Conclusion: Isaac Newton could claim two birth dates, but now his birthday is largely recognized as January 4, 1643. Newton’s work in gravity and the laws of motion form the basis of a current understanding of physics and astronomy.