Robert Rumpf wrote:
Similar to the application of topspin or backspin
Another analogy, is, I suppose the result of what you get when you hit a ball with "english
" on it in pool into another ball.
Bingo. The only difference is that (true to the motion in stillness ideal), nage/tori's motion in existing "spin" may be virtual, but uke's perception is the same. The active dampening/amplification and axis conversion of his applied force/torque at contact with tori/nage in proper ki musubi relationship and the expression of kokyu in proper technique is precisely the same in gyroscopic terms as if there were actual spin or oscillation.
That is the working theory, anyway. It fits well with the common training rubric of "think big -- act small" in terms of the movements being applied as traingn becomes more refined. Progressively one translates less and less actual movement into more and more of its virtual neuro-muscular counterpart (which I would hazard at analogizing as the measure of "kokyu power"). Certainly, this give a non-spooky basis to observe the pushing contrests O-Sensei would demonstrate with several uke or with an uke having him in obvious(?) mechanically disadvantageous position, if considered only statically.
The Segway works on this principle also, using various vibrational piezoelectric gyroscopes, as do modern "fly-by-wire" fighters, FWIW.