Keith Mack
Isaac Newton is credited with creating the laws of gravitation. Before Newton, many theories explained gravity, with the first extant sources discussing such theories found in ancient Greek philosophy. Newton's law of universal gravitation describes gravity as a force stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass.
| Characteristics | Values |
|---|---|
| Name of Astronomer | Isaac Newton |
| Law | Newton's Law of Universal Gravitation |
| Date | First published on 5 July 1687 |
| Publication | Philosophiæ Naturalis Principia Mathematica (Latin for 'Mathematical Principles of Natural Philosophy' (the Principia)) |
| Description | Describes gravity as a force stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass |
| Equation | F (force) ∝ m1 x m2 / d^2 (d = distance between the objects) |
| G (Gravitational Constant) | 6.693 × 10−11 cubic metres per kilogram second squared |
| Predecessor Theories | Theories by Aristotle, Brahmagupta, Bhāskara II, Copernicus, Tycho Brahe, Galileo Galilei, Johannes Kepler |
| Successor Theories | Albert Einstein's Theory of Relativity |
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What You'll Learn
Isaac Newton's discovery of the laws of gravitation
Isaac Newton is known for his discovery of the laws of gravitation. Before Newton's law of gravity, there were several theories explaining gravity. Philosophers like Aristotle, as early as the 4th century BC, observed objects falling and developed theories about why they fall. For instance, Aristotle thought that rocks fall to the ground because seeking the ground was an essential part of their nature. Around 1600, the scientific method began to take root, and philosophers such as René Descartes and Galileo Galilei developed more fundamental views of gravity.
Newton's law of universal gravitation describes gravity as a force stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass. This law is derived from empirical observations by what Newton called inductive reasoning. Newton's law of gravitation is a simple equation that allows us to predict the positions of all the planets, moons, and comets in the solar system and beyond.
Newton's discovery of the laws of gravitation was inspired by observing a falling apple from a tree. He wondered why the apple always fell straight to the ground and never veered off to the left or right. According to his laws of motion, anything that begins moving from a standing start is undergoing acceleration, and where there is acceleration, there must be a force. Therefore, there must be a force of attraction between the apple and the Earth.
Newton also studied the centuries of measurements from astronomers before him. By the 17th century, the German astronomer and mathematician Johannes Kepler had calculated that planets orbited the sun in elliptical paths. Kepler's laws allowed astronomers to predict the positions of the planets in the future based on past data. However, they did not explain why the planets moved around the sun. Newton filled this gap by proposing that a force acted between the bodies that were moving around each other.
Newton's law of gravitation was first published on July 5, 1687, in his work "Philosophiæ Naturalis Principia Mathematica" (Latin for "Mathematical Principles of Natural Philosophy"). His discovery of the laws of gravitation, along with his other works, is considered a turning point in the Scientific Revolution and the start of the Enlightenment.
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The influence of previous astronomers' work
Isaac Newton is credited with formulating the laws of universal gravitation. However, his work was influenced by many astronomers and scientists before him.
The ancient Greeks were the first to discuss theories of gravitation. The Greek philosopher Aristotle, who taught in the 4th century BC, believed that there is no motion without a cause. He thought that the cause of the downward motion of heavy bodies was related to their nature (gravity), which caused them to move toward the centre of the universe. He also supported the idea of a spherical Earth. Another Greek philosopher, Strato, proposed a theory of impetus to explain motion, which was adopted by the Greek astronomer Hipparchus of Nicaea. The Greek physicist Archimedes discovered the centre of mass of a triangle and also postulated that if the centres of gravity of two equal weights were not the same, it would be located in the middle of the line joining them.
In the 6th century AD, the Byzantine Alexandrian scholar John also contributed to the understanding of gravity. The Indian scholars Brahmagupta and Bhāskara II, in the 6th and 12th centuries respectively, described gravity as an attractive force, with the latter stating that the property of attraction is inherent in the Earth.
During the Renaissance and the Scientific Revolution, there were significant advancements in the understanding of gravity. The Italian polymath Galileo Galilei wrote about experimental measurements of falling and rolling objects. The German astronomer and mathematician Johannes Kepler worked out the geometry of the movements of the stars and planets. He discovered that planets orbit the sun in elliptical paths, and his three laws of planetary motion allowed astronomers to predict the positions of the planets.
When Newton arrived in Cambridge in 1661, he immersed himself in the works of Aristotle, Descartes, Galileo, and Thomas Street. He was also influenced by the French philosopher Pierre Gassendi's revival of atomism and the chemist Robert Boyle's work. Newton's laws of motion and his formulation of the law of universal gravitation built upon these previous works and observations.
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The role of the apple story
Isaac Newton is credited with formulating the laws of universal gravitation. The story goes that Newton was inspired to develop his theory of gravitation by observing an apple fall from a tree. Newton himself often recounted this anecdote, and it was later popularized by Voltaire in his "Essay on Epic Poetry" (1727). According to Voltaire's account, Newton was walking in his garden when he witnessed an apple falling from a tree, prompting him to contemplate the forces governing such motion.
While the specific details of the story may not be entirely accurate, it captures Newton's scientific thinking and his synthesis of existing knowledge. Newton built upon the work of previous scientists, such as Galileo Galilei, who conducted experiments with inclined planes to demonstrate that objects accelerate uniformly under gravity, regardless of their mass. Newton's law of universal gravitation states that every particle of matter in the universe attracts each other through the force of gravity, and his equation describes the strength of this attraction.
The apple story illustrates Newton's curiosity about the natural world and his ability to question established ideas. By observing the apple falling, Newton wondered why it always fell straight to the ground instead of veering off to the side or upward. This led him to propose the concept of a "drawing power" or force of attraction between objects, which became a fundamental principle in his laws of motion.
The apple anecdote also highlights the significance of Newton's scientific contributions. By questioning the motion of the apple, Newton was able to develop a theory that unified terrestrial and celestial mechanics. His law of universal gravitation explained phenomena such as planetary orbits and the fall of objects on Earth, demonstrating that the same principles applied to both. This unification marked a pivotal moment in scientific history and laid the foundation for future advancements in physics and astronomy.
The apple tree mentioned in the story has gained a notable status as well. The original tree, located at Woolsthorpe Manor, Newton's family estate in Lincolnshire, England, was blown down by a storm in 1820, but it regrew from its roots. Descendants and clones of the tree can now be found in various locations worldwide.
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How the laws were mathematically derived
Isaac Newton is credited with creating the laws of gravitation. Before Newton's law of gravity, there were several theories explaining gravity. Philosophers like Aristotle, as early as the 4th century BC, observed objects falling and developed theories for why they fall. For instance, he thought that rocks fall to the ground because seeking the ground was intrinsic to their nature. Around 1600, René Descartes developed ideas of matter and action independent of theology. Galileo Galilei wrote about experimental measurements of falling and rolling objects.
Newton's law of universal gravitation describes gravity as a force stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass. In other words, the strength of the gravitational force between two objects drops off in the same way that a light gets dimmer as you move away from it, a relationship known mathematically as an inverse square law. The equation for this is:
F = G(m1m2)/R^2
Where F is the force, G is the gravitational constant, m1 and m2 are the masses of the objects, and R is the distance between them.
Newton's law was formulated in his work "Philosophiæ Naturalis Principia Mathematica" (Latin for "Mathematical Principles of Natural Philosophy"), first published on July 5, 1687. The publication of the law has become known as the "first great unification" as it unified the previously described phenomena of gravity on Earth with known astronomical behaviors. It is a part of classical mechanics and was derived from empirical observations by what Newton called inductive reasoning.
Newton's theory was later superseded by Albert Einstein's theory of general relativity in the early 20th century, in which gravitation is a manifestation of curved spacetime instead of being due to a force propagated between bodies. However, Newton's law still continues to be used as an excellent approximation of the effects of gravity in most applications.
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The limitations of Newton's theory
Isaac Newton formulated the laws of gravitation in his work 'Philosophiæ Naturalis Principia Mathematica' (Latin for 'Mathematical Principles of Natural Philosophy'), which was first published on July 5, 1687.
Newton's theory of universal gravitation has several limitations. Firstly, it is only applicable in inertial frames of reference, which is a significant constraint on the concept of gravitational force. When dealing with a body in an acceleration frame of reference, pseudo force (-ma) must be included in the force equations, in addition to all other forces. Newton's laws are applicable to point objects and stiff bodies. A body is considered rigid if the relative distance between its particles remains unchanged despite any deforming force. For objects travelling at a speed comparable to light, Newton's law of motion does not match experimental results, and Einstein's special theory of relativity must be applied instead.
Newton's theory also does not fully explain the precession of the perihelion of the orbits of the planets, especially Mercury. There is a 43 arcsecond per century discrepancy between the Newtonian calculation, which considers only the gravitational attractions from the other planets, and the observed precession made with advanced telescopes in the 19th century. The predicted angular deflection of light rays by gravity, calculated using Newton's theory, is only half of the deflection observed by astronomers.
Newton's theory is also limited in its applicability to situations where either dimensionless parameter is large; in such cases, general relativity must be used to describe the system. In spiral galaxies, the orbiting of stars around their centres seems to contradict both Newton's law of universal gravitation and general relativity. Astrophysicists explain this anomaly by assuming the presence of large amounts of dark matter.
Furthermore, Newton's law is only applicable for point masses on extended bodies. It also inherently assumes that gravitation is an action-at-a-distance force, meaning that any change in the position of one mass is instantly communicated to all other masses without physical contact. This assumption is not derived from any first principle as Newton's theory does not address this question.
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Frequently asked questions
Isaac Newton formulated the laws of gravitation.
Newton was inspired by the work of astronomers before him, including Johannes Kepler, who had worked out the geometry of the movements of the stars and planets. Newton also told the story of how he saw an apple fall to the ground from a tree in his mother's garden, which made him wonder why the apple fell straight down instead of veering off to the side.
Newton's laws of gravitation describe gravity as a force stating that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centres of mass.
Newton's laws of gravitation allowed for the prediction of the positions of all the planets, moons, and comets in the solar system and beyond. They also helped engineers work out how much energy was needed to break the gravitational bonds of Earth.
Yes, there were numerous theories of gravitation before Newton's, dating back to ancient Greek philosophy. In the 6th century AD, the Byzantine Alexandrian scholar John also described a theory of gravitation. In the Middle Ages, Indian, Islamic, and European scientists furthered the work of the Greeks, and in the Renaissance and Scientific Revolution, there were great strides made in the field, culminating in Newton's formulation.
