In two dimensions, the stress tensor at a given material point P with respect to any two perpendicular directions is completely defined by only three stress components. For the particular coordinate system ( x , y ) these stress components are: the normal stresses σ σ x and σ σ y , and the shear stress τ τ x y . From the balance of angular momentum, the symmetry of the Cauchy stress tensor can be demonstrated. This symmetry implies that τ τ x y = τ τ y x . Thus, the Cauchy stress tensor can be written as: