Q.The ratio of shearing stress to the shearing strain is defined as

Shear (rigidity) modulus G = shearing stress / shearing strain, by definition -- distinct from Young's modulus (longitudinal stress/strain) and bulk modulus (volumetric stress/strain).

There are three moduli of elasticity, each defined for a different type of deformation:

• Young's modulus Y = longitudinal stress / longitudinal strain (stretching/compressing along one direction).
• Bulk modulus B = volumetric (hydraulic) stress / volumetric strain (uniform compression, e.g., under fluid pressure). …