Editing Inertia (section)

===Classical inertia===
According to science historian [[Charles Coulston Gillispie]], inertia "entered science as a physical consequence of [[Descartes]]' geometrization of space-matter, combined with the immutability of God."<ref>{{cite book |last=Gillispie |first=Charles Coulston |author-link1=Charles Coulston Gillispie |title=The Edge of Objectivity: An Essay in the History of Scientific Ideas |url=https://archive.org/details/edgeofobjectivit00char/page/367 |url-access=registration |year=1960 |publisher=Princeton University Press |isbn=0-691-02350-6 |pages=[https://archive.org/details/edgeofobjectivit00char/page/367 367–68] }}</ref> The first physicist to completely break away from the Aristotelian model of motion was [[Isaac Beeckman]] in 1614.<ref>{{Citation| last = van Berkel| first = Klaas| title = Isaac Beeckman on Matter and Motion: Mechanical Philosophy in the Making| publisher = Johns Hopkins University Press| year = 2013| url = https://books.google.com/books?id=D3WTX-23UVEC&pg=PA105| pages= 105–110| isbn = 9781421409368}}</ref> 

The term "inertia" was first introduced by [[Johannes Kepler]] in his ''[[Epitome Astronomiae Copernicanae]]''<ref>Lawrence Nolan (ed.), ''The Cambridge Descartes Lexicon'', Cambridge University Press, 2016, "Inertia.", p. 405</ref> (published in three parts from 1617 to 1621). However, the meaning of Kepler's term, which he derived from the Latin word for "idleness" or "laziness", was not quite the same as its modern interpretation. Kepler defined inertia only in terms of resistance to movement, once again based on the [[axiom|axiomatic assumption]] that rest was a natural state which did not need explanation. It was not until the later work of Galileo and Newton unified ''rest'' and ''motion'' in one principle that the term "inertia" could be applied to those concepts as it is today.<ref>{{Cite book|url=https://books.google.com/books?id=S39FDQAAQBAJ&pg=PT130|title=Restoring the Bioelectrical Machine|last=Biad|first=Abder-Rahim|date=2018-01-26|publisher=Lulu Press, Inc|isbn=9781365447709|language=en}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
The principle of inertia, as formulated by Aristotle for "motions in a void",<ref>7th paragraph of section 8, book 4 of Physica</ref> includes that a mundane object tends to resist a change in motion. <!--According to Newton, an object will stay at rest or stay in motion (i.e. maintain its velocity) unless acted on by a net external force, whether it results from [[gravity]], [[friction]], contact, or some other force.--> The Aristotelian division of motion into mundane and celestial became increasingly problematic in the face of the conclusions of [[Nicolaus Copernicus]] in the 16th century, who argued that the Earth is never at rest, but is actually in constant motion around the Sun.<ref>Nicholas Copernicus, [http://www.webexhibits.org/calendars/year-text-Copernicus.html#:~:text=revolution%20around%20the%20sun ''The Revolutions of the Heavenly Spheres''], 1543</ref>[[File:Portrait of Sir Isaac Newton, 1689.jpg|thumb|Isaac Newton, 1689]][[File:Galileo.arp.300pix.jpg|thumb|Galileo Galilei]]
[[Galileo]], in his further development of the [[Copernican model]], recognized these problems with the then-accepted nature of motion and, at least partially, as a result, included a restatement of Aristotle's description of motion in a void as a basic physical principle:

<blockquote>A body moving on a level surface will continue in the same direction at a constant speed unless disturbed.<!--><ref>For a detailed analysis concerning this issue, see Alan Chalmers's article "Galilean Relativity and Galileo's Relativity", in ''Correspondence, Invariance and Heuristics: Essays in Honour of Heinz Post'', eds. Steven French and Harmke Kamminga, Kluwer Academic Publishers, Dordrecht, 1991, {{ISBN|0792320859}}.</ref><--> </blockquote>

Galileo writes that "all external impediments removed, a heavy body on a spherical surface concentric with the earth will maintain itself in that state in which it has been; if placed in a movement towards the west (for example), it will maintain itself in that movement."<ref>{{cite web|last=Drake|first=Stillman|url=https://archive.org/details/B-001-001-741/page/n125/mode/2up?view=theater|title=Galilei's presentation of his principle of inertia, p. 113|access-date=2022-07-31}}</ref>
<!--<ref>Drake, S. ''Discoveries and Opinions of Galileo'', Doubleday Anchor, New York, 1957, pp. 113–114</ref> -->
This notion, which is termed "circular inertia" or "horizontal circular inertia" by historians of science, is a precursor to, but is distinct from, Newton's notion of rectilinear inertia.<ref>See Alan Chalmers article "Galilean Relativity and Galileo's Relativity", in ''Correspondence, Invariance and Heuristics: Essays in Honour of Heinz Post'', eds. Steven French and Harmke Kamminga, Kluwer Academic Publishers, Dordrecht, 1991, pp. 199–200, {{ISBN|0792320859}}. Chalmers does not, however, believe that Galileo's physics had a general principle of inertia, circular or otherwise. [https://books.google.com/books?id=QyMyBwAAQBAJ&pg=PA199 page 199]</ref><ref>Dijksterhuis E.J. ''The Mechanisation of the World Picture'', Oxford University Press, Oxford, 1961, [https://archive.org/details/e.j.dijksterhuisthemechanizationoftheworldpictureoxforduniversitypress1961/page/n357/mode/2up p. 352]</ref> For Galileo, a motion is "[[horizontal and vertical|horizontal]]" if it does not carry the moving body towards or away from the center of the Earth, and for him, "a ship, for instance, having once received some impetus through the tranquil sea, would move continually around our globe without ever stopping."<ref>{{cite web|last=Drake|first=Stillman|url=https://archive.org/details/B-001-001-741/page/n125/mode/2up?view=theater|title=Discoveries and Opinions of Galileo, p. 113-114|access-date=2022-07-31}}</ref><!--<ref>Galileo, ''Letters on Sunspots'', 1613 quoted in Drake, S. ''Discoveries and Opinions of Galileo'', Doubleday Anchor, New York, 1957, pp. 113–114.</ref>--><ref>According to Newtonian mechanics, if a projectile on a smooth spherical planet is given an initial horizontal velocity, it will not remain on the surface of the planet. Various curves are possible depending on the initial speed and the height of the launch. See Harris Benson ''University Physics'', New York 1991, [https://archive.org/details/universityphysic0000bens/page/268/mode/2up page 268]. If constrained to remain on the surface, by being sandwiched, say, in between two concentric spheres, it will follow a great circle on the surface of the earth, i.e. will only maintain a westerly direction if fired along the equator. See "Using great circles" [http://www.physics.oregonstate.edu/~mcintyre/COURSES/ph429_S06/slides.pdf Using great circles]</ref> It is also worth noting that Galileo later (in 1632) concluded that based on this initial premise of inertia, it is impossible to tell the difference between a moving object and a stationary one without some outside [[Inertial frame of reference|reference]] to compare it against.<ref>Galileo, ''[[Dialogue Concerning the Two Chief World Systems]]'', 1632 ([http://www.webexhibits.org/calendars/year-text-Galileo.html#:~:text=moving%20or%20nonmoving full text]).</ref> This observation ultimately came to be the basis for [[Albert Einstein]] to develop the theory of [[special relativity]].

Concepts of inertia in Galileo's writings would later come to be refined, modified, and codified by [[Isaac Newton]] as the first of his [[Newton's laws of motion|laws of motion]] (first published in Newton's work, ''[[Philosophiæ Naturalis Principia Mathematica]]'', in 1687):

<blockquote>Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.<ref>Andrew Motte's English translation:{{Citation| last = Newton| first = Isaac| title = Newton's Principia : the mathematical principles of natural philosophy| publisher = Daniel Adee| year = 1846| location = New York| url = https://archive.org/details/newtonspmathema00newtrich/page/n87/mode/2up| pages= 83}} This usual statement of Newton's law from the Motte-Cajori translation, is however misleading giving the impression that 'state' refers only to rest and not motion whereas it refers to both. So the comma should come after 'state' not 'rest'  (Koyre: Newtonian Studies London 1965 Chap III, App A)</ref></blockquote><!--><ref>{{Cite web|url=http://web.mit.edu/8.01t/www/coursedocs/current/guide.htm|title=Classical Mechanics: MIT 8.01 Course Notes|last=Dourmaskin|first=Peter|date=December 2013|website=MIT Physics 8.01|access-date=September 9, 2016}}</ref>
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Despite having defined the concept in his laws of motion, Newton did not actually use the term "inertia.” In fact, he originally viewed the respective phenomena as being caused by "innate forces" inherent in matter which resist any acceleration. Given this perspective, and borrowing from Kepler, Newton conceived of "inertia" as "the innate force possessed by an object which resists changes in motion", thus defining "inertia" to mean the ''cause'' of the phenomenon, rather than the phenomenon itself. 

However, Newton's original ideas of "innate resistive force" were ultimately problematic for a variety of reasons, and thus most physicists no longer think in these terms. As no alternate mechanism has been readily accepted, and it is now generally accepted that there may not be one that we can know, the term "inertia" has come to mean simply the phenomenon itself, rather than any inherent mechanism. Thus, ultimately, "inertia" in modern classical physics has come to be a name for the same phenomenon as described by Newton's first law of motion, and the two concepts are now considered to be equivalent.

[[File:Inertial-vs-gravitational-mass-experiment.svg|thumb|The effect of inertial mass: if pulled slowly, the upper thread breaks (a). If pulled quickly, the lower thread breaks (b).]]