Uniting Tension and Torsion

In Mary Stewart's textbook, Launching the Imagination, she addresses the use of tension and torsion. She states that tension stretches or bends an object and torsion creates a twisting movement (273). I find this very interesting because I thought that a twisting movement would just create another type of tension. So I wondered if torsion is a type of tension or if it is a concept all its own. The definition of torsion as stated by the Oxford Dictionaries is essentially how Stewart had described it, "The action of twisting or the state of being twisted, especially of one end of an object relative to the other" (oxforddictionaries.com). Neither one of these sources indicates that torsion is a subcategory of tension, however I would assume that because an object is stretched tightly (to create tension) around itself in a twisting motion (to create torsion), that the art could depict both concepts. I believe the photo below does this, even though it it titled, "Torsion Encounter", because it seems to be undergoing torsion due to the way the wood is twisting, however it also seems to be stretching as if it is falling victim to tension.

Art created by Stian Korntved Ruud