Hi Marc, not sure I get you. I certainly agree gravitational acceleration is a constant, so the gravitational force for any given mass would be constant since the force is a function of the mass.
From a more "feeling" POV (more practical, less analytic), gravity is never out of mind for me. I feel like I am sandwiched between two things. Or anti-sandwiched, hard to say. The point is ground and gravity being present together in the body and opposite in direction, creating a physical frame of reference.
Mike, I guess torque as the result of the interplay of 2 opposing forces is just considered as being not at this level in your framework? As in, we should take it step by step? I guess I should just wait and see how you mean to present it.
This is all a little difficult because I hold my bokken and feel this torsion. I can feel that it is a direct effect of what is happening in my body, and at the same time I don't disagree with your basic examples like holding a brick with one hand. I like your description of a resultant vector that is linear and convey's the ground's support, but at the same time I know that you recognize and will eventually talk about things like the hand wanting to turn over in funekogi undo:
If you look at Tohei, as an example, doing Fune-kogi undo, you can see that he actually doesn't allow his arms to rotate; having watched a number of his movements over the years, I'd say that most of Tohei's movements tend to be similarly constrained and do not exemplify what is called "natural movement".
If there is a stick or a person's limb in that hand, and they allow natural movement, the stick/limb will experience torsion, in addition to the linear force of the row-stroke. I suppose I am confusing multiple things that occur together, even though they can be (should be) treated as separate phenomena. If I allow the hand to turn, I can stay connected in a more relaxed way (in fact it is unnecessary muscle use that would be what prevents the turning of the hand). In other words allowing that spiral could be seen as a way to preserve most effortlessly the connection to the ground. Maybe you agree, but think I am getting ahead of myself? Or is this just wrong to you?