## Newton's law of universal gravitation |

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**Newton's law of universal gravitation** states that a ^{[note 1]} This is a general ^{[1]} It is a part of * Philosophiæ Naturalis Principia Mathematica* ("the

In today's language, the law states that every ^{[2]}

The equation for universal gravitation thus takes the form:

where *F* is the gravitational force acting between two objects, *m _{1}* and

The first test of Newton's theory of gravitation between masses in the laboratory was the ^{[3]} It took place 111 years after the publication of Newton's *Principia* and approximately 71 years after his death.

Newton's law of gravitation resembles

Newton's law has since been superseded by

- history
- modern form
- bodies with spatial extent
- vector form
- gravitational field
- problematic aspects
- extensions
- solutions of newton's law of universal gravitation
- see also
- notes
- references
- external links

A recent assessment (by Ofer Gal) about the early history of the inverse square law is "by the late 1670s", the assumption of an "inverse proportion between gravity and the square of distance was rather common and had been advanced by a number of different people for different reasons".

The same author does credit Hooke with a significant and even seminal contribution, but he treats Hooke's claim of priority on the inverse square point as uninteresting since several individuals besides Newton and Hooke had at least suggested it, and he points instead to the idea of "compounding the celestial motions" and the conversion of Newton's thinking away from "

Newton himself gave credit in his *Principia* to two persons: ^{[4]} (he wrote without proof that there was a force on the earth towards the sun), and ^{[5]} (wrote that all planets were attracted towards the sun). Whiteside wrote that the main influence was Borelli, because Newton had a copy of his book.^{[6]}

In 1686, when the first book of * Principia* was presented to the

In this way, the question arose as to what, if anything, Newton owed to Hooke. This is a subject extensively discussed since that time and on which some points, outlined below, continue to excite controversy.

Robert Hooke published his ideas about the "System of the World" in the 1660s, when he read to the Royal Society on March 21, 1666, a paper "On gravity", "concerning the inflection of a direct motion into a curve by a supervening attractive principle", and he published them again in somewhat developed form in 1674, as an addition to "An Attempt to Prove the Motion of the Earth from Observations".^{[8]} Hooke announced in 1674 that he planned to "explain a System of the World differing in many particulars from any yet known", based on three "Suppositions": that "all Celestial Bodies whatsoever, have an attraction or gravitating power towards their own Centers" [and] "they do also attract all the other Celestial Bodies that are within the sphere of their activity";^{[9]} that "all bodies whatsoever that are put into a direct and simple motion, will so continue to move forward in a straight line, till they are by some other effectual powers deflected and bent..."; and that "these attractive powers are so much the more powerful in operating, by how much the nearer the body wrought upon is to their own Centers". Thus Hooke clearly postulated mutual attractions between the Sun and planets, in a way that increased with nearness to the attracting body, together with a principle of linear inertia.

Hooke's statements up to 1674 made no mention, however, that an inverse square law applies or might apply to these attractions. Hooke's gravitation was also not yet universal, though it approached universality more closely than previous hypotheses.^{[10]} He also did not provide accompanying evidence or mathematical demonstration. On the latter two aspects, Hooke himself stated in 1674: "Now what these several degrees [of attraction] are I have not yet experimentally verified"; and as to his whole proposal: "This I only hint at present", "having my self many other things in hand which I would first compleat, and therefore cannot so well attend it" (i.e. "prosecuting this Inquiry").^{[8]} It was later on, in writing on 6 January 1679|80^{[11]} to Newton, that Hooke communicated his "supposition ... that the Attraction always is in a duplicate proportion to the Distance from the Center Reciprocall, and Consequently that the Velocity will be in a subduplicate proportion to the Attraction and Consequently as Kepler Supposes Reciprocall to the Distance."^{[12]} (The inference about the velocity was incorrect.^{[13]})

Hooke's correspondence with Newton during 1679–1680 not only mentioned this inverse square supposition for the decline of attraction with increasing distance, but also, in Hooke's opening letter to Newton, of 24 November 1679, an approach of "compounding the celestial motions of the planets of a direct motion by the tangent & an attractive motion towards the central body".^{[14]}

Newton, faced in May 1686 with Hooke's claim on the inverse square law, denied that Hooke was to be credited as author of the idea. Among the reasons, Newton recalled that the idea had been discussed with Sir Christopher Wren previous to Hooke's 1679 letter.^{[15]} Newton also pointed out and acknowledged prior work of others,^{[16]} including ^{[4]} (who suggested, but without demonstration, that there was an attractive force from the Sun in the inverse square proportion to the distance), and ^{[5]} (who suggested, also without demonstration, that there was a centrifugal tendency in counterbalance with a gravitational attraction towards the Sun so as to make the planets move in ellipses). D T Whiteside has described the contribution to Newton's thinking that came from Borelli's book, a copy of which was in Newton's library at his death.^{[6]}

Newton further defended his work by saying that had he first heard of the inverse square proportion from Hooke, he would still have some rights to it in view of his demonstrations of its accuracy. Hooke, without evidence in favor of the supposition, could only guess that the inverse square law was approximately valid at great distances from the center. According to Newton, while the 'Principia' was still at pre-publication stage, there were so many a-priori reasons to doubt the accuracy of the inverse-square law (especially close to an attracting sphere) that "without my (Newton's) Demonstrations, to which Mr Hooke is yet a stranger, it cannot believed by a judicious Philosopher to be any where accurate."^{[17]}

This remark refers among other things to Newton's finding, supported by mathematical demonstration, that if the inverse square law applies to tiny particles, then even a large spherically symmetrical mass also attracts masses external to its surface, even close up, exactly as if all its own mass were concentrated at its center. Thus Newton gave a justification, otherwise lacking, for applying the inverse square law to large spherical planetary masses as if they were tiny particles.^{[18]} In addition, Newton had formulated, in Propositions 43-45 of Book 1^{[19]} and associated sections of Book 3, a sensitive test of the accuracy of the inverse square law, in which he showed that only where the law of force is calculated as the inverse square of the distance will the directions of orientation of the planets' orbital ellipses stay constant as they are observed to do apart from small effects attributable to inter-planetary perturbations.

In regard to evidence that still survives of the earlier history, manuscripts written by Newton in the 1660s show that Newton himself had, by 1669, arrived at proofs that in a circular case of planetary motion, "endeavour to recede" (what was later called centrifugal force) had an inverse-square relation with distance from the center.^{[20]} After his 1679-1680 correspondence with Hooke, Newton adopted the language of inward or centripetal force. According to Newton scholar J. Bruce Brackenridge, although much has been made of the change in language and difference of point of view, as between centrifugal or centripetal forces, the actual computations and proofs remained the same either way. They also involved the combination of tangential and radial displacements, which Newton was making in the 1660s. The lesson offered by Hooke to Newton here, although significant, was one of perspective and did not change the analysis.^{[21]} This background shows there was basis for Newton to deny deriving the inverse square law from Hooke.

On the other hand, Newton did accept and acknowledge, in all editions of the *Principia*, that Hooke (but not exclusively Hooke) had separately appreciated the inverse square law in the solar system. Newton acknowledged Wren, Hooke and Halley in this connection in the Scholium to Proposition 4 in Book 1.^{[22]} Newton also acknowledged to Halley that his correspondence with Hooke in 1679-80 had reawakened his dormant interest in astronomical matters, but that did not mean, according to Newton, that Hooke had told Newton anything new or original: "yet am I not beholden to him for any light into that business but only for the diversion he gave me from my other studies to think on these things & for his dogmaticalness in writing as if he had found the motion in the Ellipsis, which inclined me to try it ..."^{[16]}

Since the time of Newton and Hooke, scholarly discussion has also touched on the question of whether Hooke's 1679 mention of 'compounding the motions' provided Newton with something new and valuable, even though that was not a claim actually voiced by Hooke at the time. As described above, Newton's manuscripts of the 1660s do show him actually combining tangential motion with the effects of radially directed force or endeavour, for example in his derivation of the inverse square relation for the circular case. They also show Newton clearly expressing the concept of linear inertia—for which he was indebted to Descartes' work, published in 1644 (as Hooke probably was).^{[23]} These matters do not appear to have been learned by Newton from Hooke.

Nevertheless, a number of authors have had more to say about what Newton gained from Hooke and some aspects remain controversial.^{[24]} The fact that most of Hooke's private papers had been destroyed or have disappeared does not help to establish the truth.

Newton's role in relation to the inverse square law was not as it has sometimes been represented. He did not claim to think it up as a bare idea. What Newton did was to show how the inverse-square law of attraction had many necessary mathematical connections with observable features of the motions of bodies in the solar system; and that they were related in such a way that the observational evidence and the mathematical demonstrations, taken together, gave reason to believe that the inverse square law was not just approximately true but exactly true (to the accuracy achievable in Newton's time and for about two centuries afterwards – and with some loose ends of points that could not yet be certainly examined, where the implications of the theory had not yet been adequately identified or calculated).^{[25]}^{[26]}

About thirty years after Newton's death in 1727, ^{[27]}^{[28]}

Other Languages

Afrikaans: Newton se Swaartekragwet

አማርኛ: የኒውተን የግስበት ቀመር

العربية: قانون الجذب العام لنيوتن

অসমীয়া: নিউটনৰ বিশ্বজনীন মহাকৰ্ষণ সূত্ৰ

asturianu: Llei de gravitación universal

azərbaycanca: Ümumdünya cazibə qanunu

বাংলা: নিউটনের মহাকর্ষ সূত্র

беларуская: Закон сусветнага прыцягнення

беларуская (тарашкевіца): Клясычная тэорыя прыцягненьня Ньютана

български: Закон за всеобщото привличане

català: Llei de la gravitació universal

čeština: Newtonův gravitační zákon

Cymraeg: Deddf disgyrchedd cyffredinol Newton

Deutsch: Newtonsches Gravitationsgesetz

eesti: Gravitatsiooniseadus

Ελληνικά: Νόμος της παγκόσμιας έλξης

español: Ley de gravitación universal

Esperanto: Neŭtona leĝo pri universala gravito

euskara: Grabitazio unibertsalaren legea

فارسی: قانون جهانی گرانش نیوتن

français: Loi universelle de la gravitation

Gaeilge: Dlí na himtharraingthe

한국어: 만유인력의 법칙

hrvatski: Newtonov zakon gravitacije

Bahasa Indonesia: Hukum gravitasi universal Newton

italiano: Legge di gravitazione universale

ქართული: მსოფლიო მიზიდულობის კანონი

қазақша: Бүкіл әлемдік тартылыс заңы

latviešu: Ņūtona vispasaules gravitācijas likums

Lëtzebuergesch: Gravitatiounsgesetz

lietuvių: Niutono gravitacijos dėsnis

magyar: Newton-féle gravitációs törvény

македонски: Њутнов закон за гравитацијата

Bahasa Melayu: Hukum kegravitian semesta Newton

Mìng-dĕ̤ng-ngṳ̄: Uâng-iū īng-lĭk dêng-lŭk

монгол: Бүх ертөнцийн таталцлын хууль

Nederlands: Gravitatiewet van Newton

日本語: 万有引力

norsk: Newtons gravitasjonslov

occitan: Lei de la gravitacion universala

ਪੰਜਾਬੀ: ਗੁਰੂਤਾਕਰਸ਼ਣ ਦਾ ਸਰਵ-ਵਿਅਾਪੀ ਨਿਯਮ

پنجابی: نیوٹن دا کھچ دا قنون

Piemontèis: Lej ëd gravitassion universal

polski: Prawo powszechnego ciążenia

português: Lei da gravitação universal

română: Legea atracției universale

සිංහල: ගුරුත්වජ ක්ෂේත්රය

Simple English: Newton's law of universal gravitation

slovenčina: Gravitačný zákon

slovenščina: Splošni gravitacijski zakon

کوردی: یاسای ڕاکێشانی گەردوونی

српски / srpski: Универзални закон гравитације

srpskohrvatski / српскохрватски: Newtonov zakon gravitacije

svenska: Newtons gravitationslag

தமிழ்: நியூட்டனின் ஈர்ப்பு விதி

українська: Закон всесвітнього тяжіння

Tiếng Việt: Định luật vạn vật hấp dẫn của Newton

文言: 萬有引力

吴语: 牛顿万有引力定律

Yorùbá: Òfin ìṣèfà àgbálá-ayé Newton

粵語: 萬有引力定律

中文: 牛顿万有引力定律