Editing Force (section)

=== Spring ===
{{main|Elasticity (physics)|Hooke's law}}
[[File:Mass-spring-system.png|upright|thumb|''F<sub>k</sub>'' is the force that responds to the load on the spring]]
A simple elastic force acts to return a [[Spring (device)|spring]] to its natural length. An [[ideal spring]] is taken to be massless, frictionless, unbreakable, and infinitely stretchable. Such springs exert forces that push when contracted, or pull when extended, in proportion to the [[displacement field (mechanics)|displacement]] of the spring from its equilibrium position.<ref>{{cite web |last=Nave |first=Carl Rod |title=Elasticity |work=HyperPhysics |publisher=University of Guelph |url=http://hyperphysics.phy-astr.gsu.edu/hbase/permot2.html |access-date=2013-10-28}}</ref> This linear relationship was described by [[Robert Hooke]] in 1676, for whom [[Hooke's law]] is named. If <math>\Delta x</math> is the displacement, the force exerted by an ideal spring equals:
<math display="block" qid=Q170282>\mathbf{F}=-k \Delta \mathbf{x},</math>
where <math>k</math> is the spring constant (or force constant), which is particular to the spring. The minus sign accounts for the tendency of the force to act in opposition to the applied load.<ref name=FeynmanVol1 />{{rp|at=ch.12}}<ref name=Kleppner />