Re: The "Jo Trick" and Similar Exercises
I think Mike gave the basic description of what is supposed to be happening when he wrote: "...the skill involves shifting the responsibility for the load-bearing (due to the push) from the jo to one of the feet." This would definitely hold up to your engineering experience and understanding of physics, etc. However, what is a bit confusing in the demonstration itself, or what might be "gnawing" at you is the element of exaggeration. Perhaps Mike is coming from a mechanical/principle point of view and you are coming from a literal point of view - therein lies the apparent discrepancy.
In a mechanical system like the body, it should always be possible to shift load-bearing responsibility to almost any part of the body regardless of where that resistance is first experienced. However, that does not necessarily mean that that shifting of load-bearing responsibility can universally maintain itself in a mechanically viable function. Hence, it is possible for Osensei to shift load-bearing responsibility from the jo to his feet, but this may not necessarily mean that he can stop even one young man from gaining the distal lever advantage without some exaggeration involved.
In this way, what one is seeing is real (from a mechanical/principle point of view), but it is also false (from a literal point of view). In that sense, I think what Mike is saying is very valid, relevant, and important, and one would miss it if he/she cannot get past the level of exaggeration involved. In addition, I also think it is important to remember that both Takeda and Osensei have had top students openly state that they were not pushing all that hard in such demonstrations, and that if they were, they would have accomplished what any literalist would imagine quite easily. Remembering the latter keeps us honest, and, in my opinion, more likely to discover those very real principles of shifting load-bearing responsibility - less likely to talk about kokyu as some kind of magical "force" (ala Lucas).