Force

=== Fictitious ===
{{main|Fictitious forces}}
There are forces that are [[frame dependent]], meaning that they appear due to the adoption of non-Newtonian (that is, [[non-inertial frame|non-inertial]]) [[Frame of reference|reference frames]]. Such forces include the [[Centrifugal force (rotating reference frame)|centrifugal force]] and the [[Coriolis force]].<ref>{{cite web |last=Mallette |first=Vincent |title= The Coriolis Force |work=Publications in Science and Mathematics, Computing and the Humanities |publisher=Inwit Publishing, Inc. |date=1982–2008 |url=http://www.algorithm.com/inwit/writings/coriolisforce.html |access-date=2008-01-04}}</ref> These forces are considered fictitious because they do not exist in frames of reference that are not accelerating.<ref name=FeynmanVol1 />{{rp|at=ch.12}}<ref name=Kleppner /> Because these forces are not genuine they are also referred to as "pseudo forces".<ref name=FeynmanVol1 />{{rp|((12-11))}}

In [[general relativity]], [[gravity]] becomes a fictitious force that arises in situations where spacetime deviates from a flat geometry.<ref>{{Cite book |last=Choquet-Bruhat |first=Yvonne |url=https://www.worldcat.org/oclc/317496332 |title=General Relativity and the Einstein Equations |date=2009 |publisher=Oxford University Press |isbn=978-0-19-155226-7 |location=Oxford |oclc=317496332 |author-link=Yvonne Choquet-Bruhat |page=39}}</ref>