This horse is in pretty sorry shape, but just to take a last swipe at it:
I'm not opposed to physical models, I'm just opposed to believing in them. :-) Let me give you an example: if you're going to push a car everyone, from grandma to the local strongman pushing a Mac truck, will use bent arms. Yet any force/vector model would surely show that this is inefficient--that you ought to keep your arms straight, arm bones lined up with the force you're applying to the car.
Anyone want to disagree? Give me a model where that's not so? Claim that it's actually better to push with absolutely straight arms?
Okay. So if the force/vector model fails so completely in such a simple case, what hope does it have of modeling a real confrontation? Instead, y'all will go teach your students to do the equivalent of pushing with straight arms and because we're all martial artists and have checked our common sense at the door, your students will actually go out and try to do it.
So yeah, play with physical models, but when they contradict experience--your own, or as captured by hundreds of years of tradition--get very suspicious of the model, not the experience.
Jon--Fascinating insight. I've never done enough Judo to understand their approach to kuzushi. Joe C suggested in the Takahashi thread that Judo-style understanding of kuzushi was what was missing from Aikido... I'd love to hear more about that. (Or play with it tonight!)
I would not always push a car with my arms.What I might do is turn my back to the car, use the power from my legs, and thus transmit the power into the car.Or I might try and keep my arms fairly close to my body then using again the leg muscles, and keeping my body low,shove like KING KONG. Maybe the car would move then??Better still I would prefer getting a tow truck to do the job, while I grasp a coke and magnum sized doughnut.
By the way if I am JoeC see that you quote above, may I say due to the differences in posture between judo/aikido
the kuzushi may not always apply? Aikido posture means instability from a push /pull from//to the side.Judo weakness is a push /pull to the back/front due to shizentai posture .The two postures in my opinion are imo incompatible.Various other significant differences between both arts are maai, footwork,contact. limited ne waza in Aikido.Limited suwariwaza in Judo.
I do think however breaking the persons balance and keeping the person in a unbalanced state
is essential whether you do judo /aikido.If you require more info from myself or in case I have not explained things as well as I might , just holler. Cheers, Joe.