Definition and Core Principle
Newton's Law of Universal Gravitation states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This means that more massive objects exert a stronger gravitational pull, and the force weakens rapidly as the distance between objects increases.
The Mathematical Formula
The law is mathematically expressed as F = G * (m1 * m2) / r², where F is the gravitational force between the two objects, m1 and m2 are their respective masses, r is the distance between their centers, and G is the gravitational constant. G is an experimentally determined constant that quantifies the strength of gravitational attraction.
Practical Example: Earth and Moon
A classic example of this law in action is the gravitational interaction between the Earth and the Moon. The Earth's immense mass exerts a gravitational pull on the Moon, keeping it in orbit, while the Moon's gravity influences Earth's tides. The specific forces involved can be calculated precisely using Newton's formula, demonstrating why the Moon doesn't fly off into space and why we experience high and low tides.
Significance and Applications
This law was revolutionary, providing a unified explanation for phenomena ranging from falling apples to the orbits of planets. It laid the groundwork for classical mechanics and helped predict the existence of Neptune. Although superseded by Einstein's General Relativity for extreme gravitational fields, it remains highly accurate and essential for understanding most astrophysical phenomena and for practical applications like spacecraft trajectories.