Newton's law of universal gravitation
Gravity as a universal force between all masses.
Newton's law of universal gravitation is a physical law that describes gravity as a force of attraction between any two particles, proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass. For spherically symmetrical objects that are separated, they attract each other as if all their mass were concentrated at their centers. The law is a general physical law derived from empirical observations through inductive reasoning, forming a core part of classical mechanics. It was formulated in Isaac Newton's work *Philosophiæ Naturalis Principia Mathematica*, first published in 1687. The publication is known as the "first great unification" because it unified the previously described phenomena of gravity on Earth with known astronomical behaviors. The equation for universal gravitation takes the form \( F = G \frac{m_1 m_2}{r^2} \), where \( F \) is the gravitational force, \( m_1 \) and \( m_2 \) are the masses, \( r \) is the distance between centers of mass, and \( G \) is the gravitational constant. Newton did not use this constant or formula, only discussing proportionality. The first laboratory test of the law between masses was the Cavendish experiment in 1798. Newton's law resembles Coulomb's law of electrical forces, as both are inverse-square laws. It was later superseded by Einstein's general relativity, but remains an excellent approximation for most applications. Newton was uncomfortable with the notion of "action at a distance" implied by his equations, calling it a great absurdity. He also made two predictions based on his gravitational theory, one of which was confirmed by the Schiehallion experiment in 1774.
- field
- Classical mechanics, physics
- known_for
- Law of universal gravitation, inverse-square law
- formulated_by
- Isaac Newton
Lore & Background
Newton's law of universal gravitation describes gravity as a force of attraction between any two particles. This force is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass. For spherically symmetrical objects that are separated, they attract each other as if all their mass were concentrated at their centers. The law is a general physical law derived from empirical observations through inductive reasoning and is a part of classical mechanics. It was formulated in Isaac Newton's work *Philosophiæ Naturalis Principia Mathematica*, first published in 1687. The law's publication is known as the "first great unification," as it united the previously described phenomena of gravity on Earth with known astronomical behaviors. Newton's law resembles Coulomb's law of electrical forces, both being inverse-square laws, though Coulomb's law uses charge in place of mass and a different constant. The law was later superseded by Albert Einstein's theory of general relativity, but it remains an excellent approximation for most applications, with relativity needed only for extreme accuracy, very strong gravitational fields, or very small distances. Newton himself was deeply uncomfortable with the notion of "action at a distance" that his equations implied, calling it a great absurdity.
Reader's Guide
Newton's law of universal gravitation marked a pivotal moment in science, unifying celestial and terrestrial mechanics under a single mathematical framework. It provided a quantitative explanation for planetary orbits, tides, and falling objects, and became a cornerstone of classical mechanics. The law resembles Coulomb's law of electrical forces, both being inverse-square laws. Although later superseded by Albert Einstein's theory of general relativity for extreme accuracy or strong gravitational fields, Newton's law remains an excellent approximation for most applications. The universality of the gravitational constant G is intact. Newton's work also sparked philosophical debate about action at a distance, which he himself found troubling. The law's legacy endures as a foundational principle of physics, taught worldwide and used in countless practical calculations.
Did You Know?
- Newton's law of universal gravitation is known as the 'first great unification' because it unified gravity on Earth with astronomical behaviors.
- Newton did not use the gravitational constant G or the formula F = G m₁m₂/r²; he only discussed proportionality.
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