ABSTRACT
In nature, we identify various stresses: mechanical, thermal, water and air, biological, and human. Generally, no matter what kind of stress is involved, it always follows an internal or external load. Internal loads result from the interactions among particles, elements, or subsystems of an object; external loads are generated by factors outside an object. One important difference between stresses and loads is that the stresses are always internal even if the loads are external. Thus, stress always occurs among the elements of a loaded object.
