View source for Newton (unit)

{{short description|Unit of force in physics}}
{{redirects|Newtons|the snack|Newtons (cookie)}}
{{Use British English Oxford spelling|date=May 2018}}
{{Use dmy dates|date=January 2024}}
{{Infobox unit
| bgcolour =
| name = newton
| image = One Newton, illustrated (transparent background).svg
| caption = Visualization of one newton of force
| standard = [[SI]]
| quantity = [[force]]
| symbol = N
| namedafter = [[Sir Isaac Newton]]
| units1 = SI base units
| inunits1     = 1 [[kilogram|kg]]⋅[[metre|m]]⋅[[second|s]]<sup>−2</sup>
| units2       = CGS units
| inunits2     = 10<sup>5</sup>&nbsp;[[dyne|dyn]]
| units3       = Imperial units
| inunits3     = {{convert|1.000000|N|lbf|disp=out}}
}}

The '''newton''' (symbol: '''N''') is the unit of [[force]] in the [[International System of Units|International System of Units (SI)]]. Expressed in terms of [[SI base units]], it is 1&nbsp;kg⋅m/s<sup>2</sup>, the force that accelerates a mass of one kilogram at one metre per second squared.

The unit is named after [[Isaac Newton]] in recognition of his work on [[classical mechanics]], specifically [[Newton's laws of motion#Newton's second law|his second law of motion]].

== Definition ==
A newton is defined as 1&nbsp;kg⋅m/s<sup>2</sup> (it is a named derived unit defined in terms of the [[SI base unit]]s).<ref name=SIBrochure9thEd>{{cite book |last=Bureau International des Poids et Mesures |url=https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.10&download=true |title=The International System of Units (SI) |publisher=[[Bureau International des Poids et Mesures]] (BIPM) |year=2019 |edition=9 |page=137 |format=PDF |access-date=22 September 2021 |archive-date=30 September 2021 |archive-url=https://web.archive.org/web/20210930221014/https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=1.10&download=true |url-status=live }}</ref>{{rp|137}} One newton is, therefore, the force needed to [[Acceleration|accelerate]] one [[kilogram]] of mass at the rate of one [[metre per second squared]] in the direction of the applied force.<ref name=":0">{{Cite web |date=17 December 2020 |title=Newton {{!}} unit of measurement |url=https://www.britannica.com/science/newton-unit-of-measurement |url-status=live |archive-url=https://web.archive.org/web/20190927032140/https://www.britannica.com/science/newton-unit-of-measurement |archive-date=27 September 2019 |access-date=27 September 2019 |work=[[Encyclopædia Britannica]]}}</ref>

The units "metre per second squared" can be understood as measuring a rate of change in [[velocity]] per unit of time, i.e. an increase in velocity by one metre per second every second.<ref name=":0" />

In 1946, the [[General Conference on Weights and Measures]] (CGPM) Resolution&nbsp;2 standardized the unit of force in the [[MKS system of units]] to be the amount needed to accelerate one kilogram of mass at the rate of one metre per second squared. In 1948, the 9th CGPM Resolution&nbsp;7 adopted the name ''newton'' for this force.<ref name="ISU1977">{{Cite book |last= |first= |url=https://books.google.com/books?id=YvZNdSdeCnEC&pg=PA17 |title=The International System of Units (SI) |publisher=[[U.S. Department of Commerce]], [[National Bureau of Standards]] |year=1977 |isbn= 9282220451 |edition=1977 |pages=17| access-date = 15 November 2015 | archive-date = 11 May 2016 | archive-url=https://web.archive.org/web/20160511160701/https://books.google.com/books?id=YvZNdSdeCnEC&pg=PA17}}</ref> The MKS system then became the blueprint for today's SI system of units.<ref name="NIST330">{{cite book |editor1=David B. Newell |editor2=Eite Tiesinga |title=The International System of Units (SI) |url=https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.330-2019.pdf |access-date=30 November 2019 |publisher=[[National Institute of Standards and Technology|NIST]] |location=Gaithersburg, MD |date=2019|edition=NIST Special publication 330, 2019}}</ref> The newton thus became the standard unit of force in the {{lang|fr|Système international d'unités}} (SI), or [[International System of Units]].<ref name="ISU1977" />

{{SI unit lowercase|Isaac Newton|newton|N}}

The connection to Newton comes from [[Newton's laws of motion|Newton's second law of motion]], which states that the force exerted on an object is directly proportional to the acceleration hence acquired by that object, thus:<ref>{{cite web | title = Table 3. Coherent derived units in the SI with special names and symbols | work = The International System of Units (SI) | publisher = [[International Bureau of Weights and Measures]] | year = 2006 |url=http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html | url-status = dead | archive-url=https://web.archive.org/web/20070618123613/http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html | archive-date = 18 June 2007 }}</ref>
<math display=block>F = ma,</math>
where <math>m</math> represents the [[mass]] of the object undergoing an acceleration <math>a</math>. When using the SI unit of mass, the kilogram (kg),  and SI units for distance [[metre]] (m), and time, [[second]] (s) we arrive at the SI definition of the newton: 1&nbsp;kg⋅m/s<sup>2</sup>.

== Examples ==

At average [[Gravity of Earth|gravity on Earth]] (conventionally, <math>g_\text{n}</math> = {{val|9.80665|u=m/s2}}), a kilogram mass exerts a force of about 9.81&nbsp;N. 
* An average-sized [[Isaac Newton#Apple incident|apple]] with mass 200&nbsp;g exerts about two newtons of force at Earth's surface, which we measure as the apple's [[weight]] on Earth.
: <math>0.200 \text{ kg} \times 9.80665 \text{ m/s}^2 = 1.961\text { N}. </math>
* An [[Human body weight#Average weight around the world|average adult]] exerts a force of about 608&nbsp;N on Earth.
: <math>62\text { kg} \times 9.80665 \text{ m/s}^2=608\text{ N} </math> (where 62&nbsp;kg is the world average adult mass).<ref>{{cite journal |last1=Walpole |first1=Sarah Catherine |last2=Prieto-Merino |first2=David |last3=Edwards |first3=Phillip |last4=Cleland |first4=John |last5=Stevens |first5=Gretchen |last6=Roberts |first6=Ian |display-authors=2 |date=18 June 2012 |title=The weight of nations: an estimation of adult human biomass |journal=[[BMC Public Health]] |volume=12 |issue=12 |page=439 |doi=10.1186/1471-2458-12-439 |pmc=3408371 |pmid=22709383 |doi-access=free }}</ref>

== Kilonewtons ==
[[File:Dwire carabiner.jpg|thumb|right|A [[carabiner]] used in [[rock climbing]], with a safety rating of 26&nbsp;kN when loaded along the spine with the gate closed, 8&nbsp;kN when loaded perpendicular to the spine, and 10&nbsp;kN when loaded along the spine with the gate open.]]
Large forces may be expressed in kilonewtons (kN), where {{nowrap|1&nbsp;kN {{=}} 1000&nbsp;N}}. For example, the [[tractive effort]] of [[NER Class Y|a Class Y steam train locomotive]] and the [[thrust]] of an [[Pratt & Whitney F100|F100 jet engine]] are both around 130&nbsp;kN.{{Citation needed|date=January 2024}}

Climbing ropes are tested by assuming a human can withstand a fall that creates 12&nbsp;kN of force. The ropes must not break when tested against 5 such falls.<ref>Bright, Casandra Marie. "A History of Rock Climbing Gear Technology and Standards." (2014).</ref>{{rp|11}}

== Conversion factors ==
{{Units of force}}
{{GravEngAbs}}
{{SI prefixes (inline table)|floatleft}}
{{clear}}

== See also ==
{{div col|colwidth=30em}}
* [[Force gauge]]
* [[International System of Units]] (SI)
* [[Joule]], SI unit of [[energy]], 1 newton exerted over a displacement of 1 metre
* [[Kilogram-force]], force exerted by Earth's gravity at sea level on one kilogram of mass
* [[Kip (unit)]]
* [[Pascal (unit)|Pascal]], SI unit of [[pressure]], 1 newton acting on an area of 1 [[square metre]]
* [[Orders of magnitude (force)]]
* [[Pound (force)]]
* [[Sthène]]
* [[Newton metre]], SI unit of [[torque]]
{{div col end}}

== References ==
{{reflist}}

{{SI units}}
{{Isaac Newton}}

[[Category:Units of force]]
[[Category:SI derived units]]
[[Category:Isaac Newton]]