In 1687 Sir Isaac Newton published his law of universal gravitation, which states that any particle of matter in the Universe is attracted to any other particle with a force that depends on their masses and the distance separating them. In a very real sense, Newton's discovery was the foundation of modern physics because it is the first universal law.
Though Newton's law is a very good approximation, in the early 20th century Albert Einstein more accurately described gravity with his theory of general relativity.
Image: A false-colour view of the Moon passing in front of the Sun. Newton's law allows us to calculate the orbits of planets and moons. (credit: NASA)
At 15,000 metres Prof Brian Cox experiences what a world without gravity would be like.
Prof Brian Cox simulates the strength of gravity on other planets through a human centrifuge in Holland.
Professor Brian Cox explains how Isaac Newton came to his understanding of gravity.
Although Newton's Law of Universal Gravitation is a good approximation of gravity, more precise measurements of the Moon's orbit show it is not a perfect explanation.
Astronomers were puzzled to find what appeared to be neighbouring, duplicate galaxies, which they named 957 and 571. It is now thought that only one galaxy, known as the Twin Quasar, exists. Its light is being bent by warped space-time just as Einstein's theory of general relativity predicts.
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their masses. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, and coalesced matter to remain intact, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe.
Gravitation is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth.
Gravitation is one of the four fundamental interactions of nature, along with electromagnetism, and the nuclear strong force and weak force. Modern physics describes gravitation using the general theory of relativity by Einstein, in which it is a consequence of the curvature of spacetime governing the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most physical situations.
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