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Before Newton's law of gravity, there were many theories explaining gravity. Philoshophers made observations about things falling down − and developed theories why they do – as early as Aristotle who thought that rocks fall to the ground because seeking the ground was an essential part of their nature.
In 1687, Isaac Newton published the Principia which contained his universal law of gravitational attraction. Five years later, Richard Bentley, a young churchman and scholar who was preparing a lecture about Newton's theories and the rejection of atheism, wrote a letter to Newton: in a finite universe, if all stars attract each other, would ...
The gravitational constant is a physical constant that is difficult to measure with high accuracy. [7] This is because the gravitational force is an extremely weak force as compared to other fundamental forces at the laboratory scale. [d] In SI units, the CODATA-recommended value of the gravitational constant is: [1]
Gravitation, also known as gravitational attraction, is the mutual attraction between all masses in the universe.Gravity is the gravitational attraction at the surface of a planet or other celestial body; [6] gravity may also include, in addition to gravitation, the centrifugal force resulting from the planet's rotation (see § Earth's gravity).
Then the attraction force vector onto a sample mass can be expressed as: = Here is the frictionless, free-fall acceleration sustained by the sampling mass under the attraction of the gravitational source. It is a vector oriented toward the field source, of magnitude measured in acceleration units.
In classical mechanics, the central-force problem is to determine the motion of a particle in a single central potential field.A central force is a force (possibly negative) that points from the particle directly towards a fixed point in space, the center, and whose magnitude only depends on the distance of the object to the center.
In theories of quantum gravity, the graviton is the hypothetical elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity.
For instance, if the gravitational acceleration equals a 0 at a distance from a mass, at ten times that distance, Newtonian gravity predicts a hundredfold decline in gravity whereas MOND predicts only a tenfold reduction. By fitting Milgrom's law to rotation curve data, Begeman et al. found a 0 ≈ 1.2 × 10 −10 m/s 2 to be optimal. [23]