== From rigidity == 

 I recently cleaned up the rigidity article. It had a short blurb describing rigidity in solid mechanics and then referenced this article. Below is the blurb and now it links to this article. I wasn't sure if any of this could be incorporated. 

  
 In solid mechanics, "rigidity" refers to the degree of deforming ability of a solid material. Modulus of elasticity with moment of inertia (E·I) is the numeric value of rigidity. According to this expression, one can see only two criteria affect deformation, which are geometry and the material of an object. Rigidity is also known as the material property of shear modulus which is a measure of force per unit area needed to change the shape of a material.