Great Scientists: Sir Isaac Newton (1642-1727) was one of the greatest scientists of recent times. He was born in England. He gave his laws of motion, equations of motion and theory of gravity in his book Principia. Before this book was written, Kepler had given three laws describing planetary motions. However, the reason why planets move in the way described by Kepler’s laws was not known. Newton, with his theory of gravity, mathematically derived Kepler’s laws. Try this Tie a stone to one end of a string. Take the other end in your hand and rotate the string so that the stone moves along a circle as shown in figure 1.2 a. Are you applying any force on the stone? In which direction is this force acting? How will you stop this force from acting? What will be the effect on the stone? As long as we are holding the string, we are pulling the stone towards us i.e. towards the centre of the circle and are applying a force towards it. The force stops acting if we release the string. In this case, the stone will fly off along a straight line which is the tangent to the circle at the position of the stone when the string is released, because that is the direction of its velocity at that instant of time (Figure 1.2 b). You may recall that we have performed a similar activity previously in which a 5 rupee coin kept on a rotating circular disk flies off the disk along the tangent to the disk. Thus, a force acts on any object moving along a circle and it is directed towards the centre of the circle. This is called the Centripetal force. ‘Centripetal’ means centre seeking, i.e. the object tries to go towards the centre of the circle because of this force. 1.2 A stone tied to a string, moving along a circular path and its velocity in tangential direction In addition to this, Newton did ground breaking work in several areas including light, heat, sound and mathematics. He invented a new branch of mathematics. This is called calculus and has wide ranging applications in physics and mathematics. He was the first scientist to construct a reflecting telescope.

🌟 Great Scientists Series: Sir Isaac Newton – The Man Who Unlocked the Universe

Introduction

Few names in the history of science carry the weight of Sir Isaac Newton (1642–1727). Revered as one of the most influential scientists of all time, Newton transformed our understanding of the natural world. His groundbreaking theories on motion, gravity, and optics laid the foundation for classical physics and reshaped how we see the universe.

Early Life and Education

Born on January 4, 1643, in Woolsthorpe, England, Newton’s early life was marked by challenges. His father died before he was born, and he was raised by his grandmother. He showed an early interest in mechanics and mathematics. Newton later studied at Trinity College, Cambridge, where he would embark on a journey of intellectual brilliance.

Newton’s Landmark Contributions

📘 Principia Mathematica – The Masterpiece

In 1687, Newton published his most famous work, "Philosophiæ Naturalis Principia Mathematica", commonly known as the Principia. In it, he introduced:

Three Laws of Motion
Law of Universal Gravitation
Derivation of Kepler’s Laws from his own

This book didn’t just introduce equations; it unified the heavens and Earth under the same set of physical laws.

⚖ Newton’s Three Laws of Motion

First Law (Law of Inertia): An object will remain at rest or in uniform motion unless acted upon by an external force.
Second Law: $F = ma$ (Force equals mass times acceleration)
Third Law: For every action, there is an equal and opposite reaction.

These laws remain fundamental in physics education and application to this day.

🌍 Law of Universal Gravitation

Newton proposed that every object in the universe attracts every other object with a force that is:

$F = \frac{G \cdot M \cdot m}{R^2}$

Where:

$F$ = Gravitational force
$G$ = Universal Gravitational Constant
$M, m$ = Masses of the two objects
$R$ = Distance between their centers

This law explained why apples fall from trees and why planets orbit the Sun—linking earthly phenomena with celestial motions.

🔭 Reflecting Telescope

Newton was also the first person to design and build a reflecting telescope, using mirrors instead of lenses. This design solved issues with chromatic aberration in refracting telescopes and is still used today in modern telescopes.

🌈 Newton’s Work in Light and Optics

Newton demonstrated that white light is composed of a spectrum of colors. He passed light through a prism and showed how it splits into a rainbow. His book "Opticks" detailed his experiments and theories on the nature of light.

🧮 Inventor of Calculus

Independently of Leibniz, Newton developed Calculus, which he called the method of fluxions. This mathematical breakthrough provided tools to model motion, growth, and change—and is now a core branch of mathematics used in science and engineering.

🎓 Contribution to Kepler's Laws

Before Newton, Johannes Kepler had described how planets move (Kepler’s Laws), but no one could explain why. Newton’s Law of Gravitation provided the mathematical basis for these laws, proving that planetary orbits result from gravitational force and motion.

🎯 The Concept of Centripetal Force

Newton explained that any object moving in a circular path experiences a force pulling it toward the center—this is the centripetal force. For example, when a stone tied to a string is spun, the tension in the string acts as the centripetal force.

“Centripetal” means center-seeking—the force is always directed toward the center of the circular path.

🎖 Legacy and Recognition

Knighted by Queen Anne in 1705.
Served as President of the Royal Society.
Buried with honors at Westminster Abbey, a rare distinction for a scientist.

💬 Famous Quotes by Newton

“If I have seen further, it is by standing on the shoulders of giants.”

“To every action, there is always opposed an equal reaction.”

🔍 Did You Know?

Newton never married.
He once held a high administrative post at the Royal Mint, reforming England’s currency.
He practiced alchemy and wrote theological papers—rare for a scientist.

Conclusion

Sir Isaac Newton’s genius forever changed how we understand the universe. From a curious boy in rural England to a scientific legend, Newton’s discoveries still power space missions, inspire classrooms, and guide researchers. His legacy is not just in books and equations—but in the way humanity perceives the cosmos.

Great Scientists Series: Sir Isaac Newton