Abstract: In this paper, the equilibrium equations on orlhogonal curve coordinates made ofcurves of principal stresses are disscused and their properties in process of solution arepresented through a simple example. Therefore, it is deduced that there is another wayto solve problems in elasticity, i.e., by assumption of orthogonal curves of principalstresses.

Key words: elasticity, equilibrium equation, principal stress, plane problem, orthogonal curve coordinates