Reciprocity of Reactions, Principle of

(also called Rayleigh’s Theorem), a property of a body that is being linearly deformed that follows from the principle of reciprocity of work; it consists in the fact that the reaction r_ki that arises in link k when link / shifts by a unit in its own direction is equal to the reaction r_ik in link / when link k shifts by a unit in its own direction—that is, r_ki= r_ik. The principle of reciprocity of reactions is used in strength of materials and structural mechanics in the calculation of statistically undefinable systems by the method of displacements.