In a static problem of the deformed body mechanics, all the forces depending on their availability in the equation resolution system are classified as surface forces Pi, volume forces Fi and distortions or forced strains (xi) . It is known that there is partial equivalence of force which means an identify equality (analogy) of stresses or displacements under the action of different types of loads; in particular, between volume and surface force actions though under very strict limitations. It is easy to demonstrate that by introducing the third constituent -- a forced strain -- it appears to be possible to establish the necessary and sufficient conditions for the analogy. These conditions make it possible to present a forced strain action as the sum of volume and surface force actions; volume forces -- as the sum of surface force effects and forced strains; surface forces -- as the sum of forced strains and volume forces. The analogy in question is very important for the experimental solution of the problem because the realization of every force is limited by modeling technique's possibilities.