Explanation
Gravity as a concept was not discovered in one moment by a single person. Many thinkers contributed ideas over centuries.
However, Sir Isaac Newton (1642–1727) is credited with formulating the first clear, mathematical law of universal gravitation.
Newton showed that the same force that makes objects fall on Earth also governs the motion of the Moon and planets.
Newton’s Contribution
Newton proposed the Law of Universal Gravitation in 1687 in his famous book
Philosophiæ Naturalis Principia Mathematica.
The formula for gravitational force is:
F = G · (m₁ m₂) / r²
- F = gravitational force
- m₁ and m₂ = masses of the two bodies
- r = distance between their centers
- G = gravitational constant
Newton’s work explained why apples fall, why planets orbit the Sun, and helped make accurate predictions of planetary motion.
What Came Before Newton
- Ancient thinkers observed falling objects and celestial motion but lacked a universal law.
- Aristotle believed heavier objects fell faster — an idea proven wrong later.
- During the Renaissance, Galileo Galilei (1564–1642) studied motion experimentally.
- Galileo showed that all bodies fall with the same acceleration in the absence of air resistance.
- His work prepared the foundation for Newton’s theory.
Measuring Gravity
Newton proposed the law, but the value of G (gravitational constant) was not known until later.
In 1798, Henry Cavendish performed the famous Cavendish experiment, measuring G for the first time.
This allowed scientists to calculate Earth’s mass and density.
Modern View: Einstein
In 1915, Albert Einstein introduced a new theory of gravity called General Relativity.
- Einstein explained gravity as the curvature of spacetime caused by mass and energy.
- Newton’s formula works well for everyday conditions.
- Einstein’s theory is needed for strong gravity (like black holes) or precise systems (like GPS satellites).
Common Anecdote
The story of Newton being inspired by a falling apple is famous but likely simplified.
It symbolizes how everyday observations sparked deeper thinking about gravity.
Important Numerical Facts
- Acceleration due to gravity near Earth’s surface: g ≈ 9.8 m/s²
- Newton’s formula: F = G m₁ m₂ / r²
- Cavendish’s experiment measured G for the first time.
Summary Points (Quick Recall)
- Gravity was developed gradually, but Newton gave the first universal mathematical law.
- Galileo corrected earlier ideas and proved key facts about falling objects.
- Cavendish measured the gravitational constant.
- Einstein redefined gravity as spacetime curvature.
- For school-level problems, use Newton’s law and g = 9.8 m/s².