Editing Torsion spring (section)

==Torsion coefficient==
As long as they are not twisted beyond their [[elastic limit]], torsion springs obey an angular form of [[Hooke's law]]:

:<math> \tau = -\kappa\theta\,</math>

where

* <math>\tau\,</math> is the torque exerted by the spring in [[newton (unit)|newton]]-meters, and <math>\theta\,</math> is the angle of twist from its equilibrium  position in [[radian]]s

* <math>\kappa\,</math> is a constant with units of newton-meters / radian, variously called the spring's '''torsion coefficient''', '''torsion elastic modulus''', '''rate''', or just '''spring constant''', equal to the change in torque required to twist the spring through an angle of 1 radian. 

The [[torsion constant]] may be calculated from the geometry and various material properties. It is analogous to the spring constant of a linear spring.  The negative sign indicates that the direction of the torque is opposite to the direction of twist.

The energy ''U'', in [[joule]]s, stored in a torsion spring is:<ref>{{cite web | url=https://www.brown.edu/Departments/Engineering/Courses/En4/Notes/particles_work_energy/particles_work_energy.htm | title=Dynamics and Vibrations: Conservation Laws for Particles: Work and Energy }}</ref>

:<math> U = \frac{1}{2}\kappa\theta^2</math>