Editing Coil spring (section)

{{Short description|Mechanical device that stores energy}}
{{More footnotes|date=December 2007}}
[[file:Ressort de traction à spires jointives.jpg|thumb|A tension coil spring]]

A '''coil spring''' is a mechanical device that typically is used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. It is made of an [[Elasticity (physics)|elastic]] material formed into the shape of a [[helix]] that returns to its natural length when unloaded.

Under tension or compression, the material (wire) of a coil spring undergoes torsion. The spring characteristics therefore depend on the [[shear modulus]].

A coil spring may also be used as a [[torsion spring]]: in this case the spring as a whole is subjected to torsion about its helical axis. The material of the [[Spring (device)|spring]] is thereby subjected to a [[bending moment]], either reducing or increasing the helical radius. In this mode, it is the [[Young's modulus]] of the material that determines the spring characteristics.