Define rigidity modulus. Give the expression for rigidity modulus.

Explanation

Rigidity modulus is defined as the ratio of tangential stress to shearing strain.
i.e. `eta=("tagential stress")/("shearing strain")`
For a tangential force acting on the surface of a block and for a small angle of shearing.
`eta=F/(A theta)` when `tan theta^(@)~~theta("rad")=(Deltax)/(L` where `Deltax` is a small.