Editing Newton's laws of motion (section)

===First law{{anchor|Newton's_first_law}}===
[[File:Skylab and Earth Limb - GPN-2000-001055.jpg|alt=see caption|thumb|Artificial satellites move along curved [[orbit]]s, rather than in straight lines, because of the Earth's [[gravity]].]]
Translated from Latin, Newton's first law reads,
:''Every object 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.''{{refn|group=note|Per Cohen and Whitman.<ref name="Cohen&Whitman" /> For other phrasings, see Eddington<ref>{{Cite book |title=The Nature of the Physical World |first=Arthur |last=Eddington |pages=123–125 |date=1929 |publisher=Macmillan |location=New York |author-link=Arthur Eddington}}</ref> and Frautschi et al.<ref name=":0">{{Cite book|last1=Frautschi|first1=Steven C.|title=The Mechanical Universe: Mechanics and Heat|title-link=The Mechanical Universe|last2=Olenick|first2=Richard P.|last3=Apostol|first3=Tom M.|last4=Goodstein|first4=David L.|date=2007|publisher=Cambridge University Press|isbn=978-0-521-71590-4|edition=Advanced|location=Cambridge [Cambridgeshire]|oclc=227002144|author-link=Steven Frautschi|author-link3=Tom M. Apostol|author-link4=David L. Goodstein}}</ref>{{Rp|page=114}} Andrew Motte's 1729 translation rendered Newton's "nisi quatenus" as ''unless'' instead of ''except insofar,'' which Hoek argues was erroneous.<ref>{{Cite journal |journal=Philosophy of Science |date=2023 |title=Forced Changes Only: A New Take on Inertia |arxiv=2112.02339 |doi=10.1017/psa.2021.38 |pages=60–73 |volume=90 |issue=1 |first=D. |last=Hoek}}</ref><ref>{{Cite journal |journal=Scientific American |date=5 September 2023 |title=Mistranslation of Newton's First Law Discovered after Nearly Nearly 300 Years |pages= |volume= |issue= |first=Stephanie |last=Pappas |url=https://www.scientificamerican.com/article/mistranslation-of-newtons-first-law-discovered-after-nearly-300-years1/}}</ref>}}
Newton's first law expresses the principle of [[inertia]]: the natural behavior of a body is to move in a straight line at constant speed. A body's motion preserves the status quo, but external forces can perturb this.

The modern understanding of Newton's first law is that no [[inertial observer]] is privileged over any other. The concept of an inertial observer makes quantitative the everyday idea of feeling no effects of motion. For example, a person standing on the ground watching a train go past is an inertial observer. If the observer on the ground sees the train moving smoothly in a straight line at a constant speed, then a passenger sitting on the train will also be an inertial observer: the train passenger ''feels'' no motion. The principle expressed by Newton's first law is that there is no way to say which inertial observer is "really" moving and which is "really" standing still. One observer's state of rest is another observer's state of uniform motion in a straight line, and no experiment can deem either point of view to be correct or incorrect. There is no absolute standard of rest.<ref>{{cite book|last=Resnick |first=Robert |author-link=Robert Resnick |title=Introduction to Special Relativity |publisher=Wiley |year=1968 |pages=8–16 |oclc=1120819093}}</ref><ref name=":0"/>{{rp|62–63}}<ref name=":2" />{{rp|7–9}} Newton himself believed that [[absolute space and time]] existed, but that the only measures of space or time accessible to experiment are relative.<ref>{{Cite journal|last=Brading|first=Katherine|author-link=Katherine Brading|date=August 2019|title=A note on rods and clocks in Newton's Principia|url=https://linkinghub.elsevier.com/retrieve/pii/S135521981730120X|journal=[[Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics]]|language=en|volume=67|pages=160–166|doi=10.1016/j.shpsb.2017.07.004|bibcode=2019SHPMP..67..160B |s2cid=125131430 }}</ref>