Erick Mead

I am not proud at all, I just understand inertial moments in a structure.You, evidently, do not. Linear inertia diminishes the quantity of a force (without effort). An inertial moment also alters its direction of effect (also without effort). They "convert" forces from one perpendicular component to the other without any active "force vector" on their part. "Juji" + , again

Even a resting object is not without inertial energy. It is the most "relaxed" form of response to force that there is. You can't even get rid of it if you wanted to.

You are disregarding the fact that we are talking about forces and reactions in different parts of the structure, which means force couples and moments of inertia in the structure between those locations. It is exceedingly rare that you can push directly in line with the center of mass -- and you have defined a problem (the chest push) where you specifically do not. Thus, there is a rotational element and a radius forming a moment of inertia about a certain axis of the structure.

In this setting, I can define the dolly problem where your push on the chest causes inertial moment to make the dolly shift toward the pusher (negative displacement). I can define the dolly problem where the same push results in the dolly shifting away from the pusher (positive displacement). This is quite obvious in iriminage (negative displacement) and kaitennage (positive displacement), for example, where I am directly manipulating those respective positive and negative rotational moments of the body.

And there is (obviously) a case in between the positive and negative regimes at which zero is attained. However, it is supercritical (top of the hill), and it takes constant energy to maintain from falling away one way or the other.

This, to me, is the antithesis of "relaxation." It is a very expensive zero.

Keeping at zero has everything to do with the shape of the load path and the conditions of support at the base, but has not a thing to do with horizontal friction. If horizontal frictional reaction would develop as a means of opposing the moment at the ground, then in frictionless setting (such as the dolly), the dolly moves one way or the other.

So if you are using ground friction, as opposed to some other means to maintain the supercritical zero displacement regime, then you will move if put on the dolly. Which was really my only point.

In the Tohei video, if he were put on a dolly, on my analysis he ought to be moved toward the attacker as he commences his attacking motion and be moved away from the attacker as he experiences kuzushi. Tohei would be moved (by the attackers own motion) through the zero regime and back again -- not be precariously maintaining himself in the middle -- not moving. It would look very much like torifune/funatori. Surprise, surprise.

I have my doubts whether maintaining this zero regime for an arbitrary length of time is of much use in aikido -- The supercritical nature of an unanticipated change of sign and the sudden downhill slide in the reverse orientation to what was expected are elements that aikido seems most readily to exploit. The load path considerations are important (which I have not really addressed). The load path defines where hinges naturally develop in either partner. Those are more important in most aikido technique than manipulating conditions of support so as "not be moved."

In other words done properly -- we move -- but always in the neighborhood of that highly critical stability area. It confounds an attack by suddenly changing the orientation of the inertial response that develops from receiving the energy of the attack at the moment of musubi or connection. If we do it perfectly, we let our body shape do the work for us, without any effort.