Gravity

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  • Gravity
definition
  • The natural phenomenon by which physical bodies appear to attract each other with a force proportional to their masses. It is most commonly experienced as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. The phenomenon of gravitation itself, however, is a byproduct of a more fundamental phenomenon described by general relativity, which suggests that spacetime is curved according to the energy and momentum of whatever matter and radiation are present.
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Abstract from DBPedia
    In physics, gravity (from Latin gravitas 'weight') is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes tides in the oceans. Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circulation of fluids in multicellular organisms. Investigation into the effects of weightlessness has shown that gravity may play a role in immune system function and cell differentiation within the human body. The gravitational attraction between the original gaseous matter in the Universe allowed it to coalesce and form stars which eventually condensed into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become weaker as objects get farther away. Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as the curvature of spacetime, caused by the uneven distribution of mass, and causing masses to move along geodesic lines. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them: where F is the force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant. Current models of particle physics imply that the earliest instance of gravity in the Universe, possibly in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch (up to 10−43 seconds after the birth of the Universe), possibly from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a currently unknown manner. Scientists are currently working to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three fundamental interactions of physics.

    重力(じゅうりょく)とは、以下の概念のいずれかを指して用いられる。 * 地球上で物体が地面に近寄っていく現象や、それを引き起こすとされる「力」。人々が日々、物を持った時に感じているいわゆる「重さ」を作り出す原因となる力。 * 物体が他の物体に引きよせられる現象。および(その現象は《力》が引き起こしていると見なす場合の)その「力」。 * その物体の質量によって生じる時空の歪みが他の物体を引き寄せる作用。 重力に関する言葉は、英語の gravity の頭文字を取って G と略されることがある。たとえば、物理学の文献においては慣習的に、天体の表面重力を小文字の g、万有引力定数を大文字の G を用いて表す。日本語の「重力」は、オランダ語の zwaartekracht を「zwaarte(重さ)」と「kracht(力)」に分けて意訳されたものである。また、重力の働く場所が一点に集中したと考えたとき、それは重心である。

    (Source: http://dbpedia.org/resource/Gravity)

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