Can young's modulus of a solid be different for extension(tensile) and compressive stress?

What is the difference betwen pressure and stress?

In nature, the failure of structural members usually result from large torque because of twisting or bending rather than due to tensile or compressive strains. This process of structural breakdown is called buckling and in cases of tall cylindrical structureslike trees, the torque is caused by its own weight bending the structure. Thus the vertical through the centre of gravity does not fall within the base. The elastic torque caused because of this bending about the central axis of the tree is given by (Ypir^4)/(4R) . Y is the Young's modulus, r is the radius of the trunk and R is the radius of curvature of the bent surface along the height of the tree containing the centre of gravity (the neuttral surface). EStimate the critical height of a tree for a given radius of the trunk.

A steel rod of length 2l, cross sectional area A and mass M is set rotating in a horizontal plane about an axis passing through the centre. If Y is the Young's modulus for steel, find the extension in the length of the rod. (assume the rod is uniform).

Define Young's modulus of elasticitiy. normal stress and longitudinal strain. Give unit of each of them. Derive an expression for the elastic potential energy of a wire, when stretched.