Editing Friction (section)

====Approximate coefficients of friction====
{{Disputed section|date=November 2021}}
{| class="wikitable"
|-
! colspan="2" rowspan="2" data-sort-type="text"|Materials !! colspan="2"|Static Friction, <math>\mu_\mathrm{s}</math> !! colspan="2"|Kinetic/Sliding Friction, <math>\mu_\mathrm{k}\,</math>
|-
|-
!data-sort-type="number"| Dry and clean !!data-sort-type="number"| Lubricated
!data-sort-type="number| Dry and clean !!data-sort-type="number"| Lubricated
|-
! Aluminium
! Steel
| 0.61<ref name="Friction Factors">{{cite web
| url = http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm#method
| title = Friction Factors – Coefficients of Friction
| access-date = 2015-04-27
| archive-url = https://web.archive.org/web/20190201171526/http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm#method
| archive-date = 2019-02-01

}}</ref>
|
| 0.47<ref name="Friction Factors"/>
|
|-
!Aluminium
!Aluminium
|1.05–1.35<ref name="Friction Factors"/>
|0.3<ref name="Friction Factors"/>
|1.4<ref name="Friction Factors"/>–1.5{{cn|date=March 2024}}
|-
!Gold
!Gold
|
|
|2.5{{cn|date=March 2024}}
|
|-
!Platinum
!Platinum
|1.2<ref name="Friction Factors"/>
|0.25<ref name="Friction Factors"/>
|3.0{{cn|date=March 2024}}
|
|-
!Silver
!Silver
|1.4<ref name="Friction Factors"/>
|0.55<ref name="Friction Factors"/>
|1.5{{cn|date=March 2024}}
|
|-
! Alumina ceramic
! Silicon nitride ceramic
|
|
|
| 0.004 (wet)<ref name="Ferreira-2012">{{cite journal
| title = Ultra-low friction coefficient in alumina–silicon nitride pair lubricated with water
| doi=10.1016/j.wear.2012.07.030
| volume=296
| issue = 1–2
| journal=Wear
| pages=656–659| date = 2012-08-30
| last1 = Ferreira
| first1 = Vanderlei
| last2 = Yoshimura
| first2 = Humberto Naoyuki
| last3 = Sinatora
| first3 = Amilton
}}</ref>
|-
! [[Aluminium magnesium boride|BAM (Ceramic alloy AlMgB<sub>14</sub>)]]
! [[Titanium boride]] (TiB<sub>2</sub>)
| 0.04–0.05<ref name="Tian-2003">{{cite journal|doi=10.1063/1.1615677|title=Superhard self-lubricating AlMgB[sub 14] films for microelectromechanical devices|year=2003|last1=Tian|first1=Y.|last2=Bastawros|first2=A. F.|last3=Lo|first3=C. C. H.|last4=Constant|first4=A. P.|last5=Russell|first5=A.M.|last6=Cook|first6=B. A.|journal=Applied Physics Letters|volume=83|issue=14|page=2781|bibcode=2003ApPhL..83.2781T|url=http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1004&context=mse_pubs|access-date=2019-01-31|archive-date=2024-10-07|archive-url=https://web.archive.org/web/20241007090944/https://dr.lib.iastate.edu/handle/20.500.12876/55639/|url-status=live}}</ref>
| 0.02<ref name="Kleiner, Kurt-2008">{{cite web
| url = https://www.newscientist.com/article/dn16102-material-slicker-than-teflon-discovered-by-accident.html
| title = Material slicker than Teflon discovered by accident
| author = Kleiner, Kurt
| date = 2008-11-21
| access-date = 2008-12-25
| archive-date = 2008-12-20
| archive-url = https://web.archive.org/web/20081220162702/http://www.newscientist.com/article/dn16102-material-slicker-than-teflon-discovered-by-accident.html
| url-status = live
}}</ref><ref name="Higdon-2011">{{cite journal|doi=10.1016/j.wear.2010.11.044
| title=Friction and wear mechanisms in AlMgB14-TiB2 nanocoatings
| year=2011|last1=Higdon|first1=C.|last2=Cook|first2=B.|last3=Harringa|first3=J.
| last4=Russell|first4=A.|last5=Goldsmith|first5=J.|last6=Qu|first6=J.|last7=Blau|first7=P.|journal=Wear|volume=271|issue=9–10
| pages=2111–2115}}</ref>
|
|
|-
! Brass
! Steel
| 0.35–0.51<ref name="Friction Factors"/>
| 0.19<ref name="Friction Factors"/>
| 0.44<ref name="Friction Factors"/>
|
|-
! Cast iron
! Copper
| 1.05<ref name="Friction Factors"/>
|
| 0.29<ref name="Friction Factors"/>
|
|-
! Cast iron
! Zinc
| 0.85<ref name="Friction Factors"/>
|
| 0.21<ref name="Friction Factors"/>
|
|-
! Concrete
! Rubber
| 1.0
| 0.30 (wet)
| 0.6–0.85<ref name="Friction Factors"/>
| 0.45–0.75 (wet)<ref name="Friction Factors"/>
|-
! Concrete
! Wood
| 0.62<ref name="Friction Factors"/><ref name="Coefficient of Friction Archived March 8"/>
|
|
|
|-
! Copper
! Glass
| 0.68<ref name="Barrett-1990" />
|
| 0.53<ref name="Barrett-1990" />
|
|-
! Copper
! Steel
| 0.53<ref name="Barrett-1990" />
|
| 0.36<ref name="Friction Factors"/><ref name="Barrett-1990" />
| 0.18<ref name="Barrett-1990" />
|-
! Glass
! Glass
| 0.9–1.0<ref name="Friction Factors"/><ref name="Barrett-1990" />
| 0.005–0.01<ref name="Barrett-1990" />
| 0.4<ref name="Friction Factors"/><ref name="Barrett-1990" />
| 0.09–0.116<ref name="Barrett-1990" />
|-
! Human synovial fluid
! Human cartilage
|
| 0.01<ref name="Coefficients of Friction of Human Joints">{{cite web
| url = http://hypertextbook.com/facts/2007/ConnieQiu.shtml
| title = Coefficients of Friction of Human Joints
| access-date = 2015-04-27
| archive-date = 2024-10-07
| archive-url = https://web.archive.org/web/20241007090943/https://hypertextbook.com/facts/2007/ConnieQiu.shtml
| url-status = live
}}</ref>
|
| 0.003<ref name="Coefficients of Friction of Human Joints"/>
|-
! Ice
! Ice
| 0.02–0.09<ref name="The Engineering Toolbox"/>
|
|
|
|-
! [[Polyethene]]
! Steel
| 0.2<ref name="Friction Factors"/><ref name="The Engineering Toolbox"/>
| 0.2<ref name="Friction Factors"/><ref name="The Engineering Toolbox"/>
|
|
|-
! [[PTFE]] (Teflon)
! PTFE (Teflon)
| 0.04<ref name="Friction Factors"/><ref name="The Engineering Toolbox">{{cite web
| url = http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
| title = The Engineering Toolbox: Friction and Coefficients of Friction
| access-date = 2008-11-23
| archive-date = 2013-12-03
| archive-url = https://web.archive.org/web/20131203000601/http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
| url-status = live
}}</ref>
| 0.04<ref name="Friction Factors"/><ref name="The Engineering Toolbox"/>
|
| 0.04<ref name="Friction Factors"/>
|-
! Steel
! Ice
| 0.03<ref name="The Engineering Toolbox"/>
|
|
|
|-
! Steel
! PTFE (Teflon)
| 0.04<ref name="Friction Factors"/>−0.2<ref name="The Engineering Toolbox"/>
| 0.04<ref name="Friction Factors"/>
|
| 0.04<ref name="Friction Factors"/>
|-
! Steel
! Steel
| 0.74<ref name="Friction Factors"/>−0.80<ref name="The Engineering Toolbox"/>
| 0.005–0.23<ref name="Barrett-1990" /><ref name="The Engineering Toolbox"/>
| 0.42–0.62<ref name="Friction Factors"/><ref name="Barrett-1990" />
| 0.029–0.19<ref name="Barrett-1990" />
|-
! Wood
! Metal
| 0.2–0.6<ref name="Friction Factors"/><ref name="Coefficient of Friction Archived March 8"/>
| 0.2 (wet)<ref name="Friction Factors"/><ref name="Coefficient of Friction Archived March 8"/>
| 0.49<ref name="Barrett-1990" />
| 0.075<ref name="Barrett-1990" />
|-
! Wood
! Wood
| 0.25–0.62<ref name="Friction Factors"/><ref name="Coefficient of Friction Archived March 8">[http://www.engineershandbook.com/Tables/frictioncoefficients.htm Coefficient of Friction] {{webarchive |url=https://web.archive.org/web/20090308124246/http://www.engineershandbook.com/Tables/frictioncoefficients.htm |date=March 8, 2009 }}. EngineersHandbook.com</ref><ref name="Barrett-1990">{{cite journal |last1=Barrett |first1=Richard T. |title=(NASA-RP-1228) Fastener Design Manual |url=http://hdl.handle.net/2060/19900009424 |website=NASA Technical Reports Server |publisher=NASA Lewis Research Center |access-date=3 August 2020 |page=16 |date=1 March 1990 |hdl=2060/19900009424 |archive-date=7 October 2024 |archive-url=https://web.archive.org/web/20241007091010/https://ntrs.nasa.gov/citations/19900009424 |url-status=live }}</ref>
| 0.2 (wet)<ref name="Friction Factors"/><ref name="Coefficient of Friction Archived March 8"/>
| 0.32–0.48<ref name="Barrett-1990" />
| 0.067–0.167<ref name="Barrett-1990" />
|}

Under certain conditions some materials have very low friction coefficients. An example is (highly ordered pyrolytic) graphite which can have a friction coefficient below 0.01.<ref>{{cite journal |last=Dienwiebel |first=Martin |title=Superlubricity of Graphite |display-authors=etal |journal=Phys. Rev. Lett. |volume=92 |page=126101 |year=2004 |doi=10.1103/PhysRevLett.92.126101 |url=http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf |issue=12 |bibcode=2004PhRvL..92l6101D |pmid=15089689 |s2cid=26811802 |access-date=2011-09-01 |archive-date=2011-09-17 |archive-url=https://web.archive.org/web/20110917120623/http://www.physics.leidenuniv.nl/sections/cm/ip/group/PDF/Phys.rev.lett/2004/92(2004)12601.pdf |url-status=live }}</ref>
This ultralow-friction regime is called [[superlubricity]].<ref>{{Citation |last=Müser |first=Martin H. |title=Theoretical Studies of Superlubricity |date=2015 |work=Fundamentals of Friction and Wear on the Nanoscale |pages=209–232 |editor-last=Gnecco |editor-first=Enrico |url=https://link.springer.com/10.1007/978-3-319-10560-4_11 |access-date=2025-04-25 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-10560-4_11 |isbn=978-3-319-10559-8 |editor2-last=Meyer |editor2-first=Ernst}}</ref>