<P> where stress is the force causing the deformation divided by the area to which the force is applied and strain is the ratio of the change in some parameter caused by the deformation to the original value of the parameter . If stress is measured in pascals, then since strain is a dimensionless quantity, the units of λ will be pascals as well . </P> <P> Specifying how stress and strain are to be measured, including directions, allows for many types of elastic moduli to be defined . The three primary ones are: </P> <Ol> <Li> Young's modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain . It is often referred to simply as the elastic modulus . </Li> <Li> The shear modulus or modulus of rigidity (G or μ (\ displaystyle \ mu \,)) describes an object's tendency to shear (the deformation of shape at constant volume) when acted upon by opposing forces; it is defined as shear stress over shear strain . The shear modulus is part of the derivation of viscosity . </Li> <Li> The bulk modulus (K) describes volumetric elasticity, or the tendency of an object to deform in all directions when uniformly loaded in all directions; it is defined as volumetric stress over volumetric strain, and is the inverse of compressibility . The bulk modulus is an extension of Young's modulus to three dimensions . </Li> </Ol> <Li> Young's modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain . It is often referred to simply as the elastic modulus . </Li>

Define young's modulus and modulus of rigidity
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