View Single Post
Old 10-02-2006, 12:41 PM   #84
Erick Mead
 
Erick Mead's Avatar
Dojo: Big Green Drum (W. Florida Aikikai)
Location: West Florida
Join Date: Jun 2005
Posts: 2,505
United_States
Offline
Re: What is "Aikido"?

Quote:
Mike Sigman wrote:
Naw... I already did it concisely and with illustrations involving Tohei in a previous post to the forum. I did it completely enough that anything missing can be extrapolated. It's far simpler than you're making it. "Hip gyration" isn't needed, since mainly linear forces are involved.
And here I thought tenkan actually meant something was turning.

Mike, really now, with over 1500 posts to your name, maybe just pointing to one or two? I could just as easily have said "Pull out the physics text -- it's in there." I tendered a tad more effort to your gauntlet to address the specific example, which is what I asked you to give me to do. Thank you, BTW.

I asked for your illustration on this example YOU proffered so we can compare notes for the benefit of everyone. It seemed that you were more than adequately prepared to do that. Do you want to engage this discussion or pretend that it is not occurring? You may yet blow me out of the water, which I am prepared to receive ukemi for. If you have the stuff to show, in concrete examples such as this, do it.
Quote:
Mike Sigman wrote:
I think the problem is that you see an object flying straight through the air and you're positing "Oh, it must have been flung from a spinning turntable". I'm saying that an object flying straight through the air came from a more linear device (similar to a pogo-stick) and that the actual power of the device is dependent upon how strong its spring constant is.
Any obect in eccentric rotation that is released from its centripetal contraint will follow a linear path perpendicular to the centripetal contraint in rotation at the moment of release. If the constraint is eccentric to the CG of the object, and the release is not instaneous, it may impart an internal rotation in the plane of the original rotation as well (think frisbee), unless you think that is also done by pushing springs. I note that not only does uke fly back, but he is rotating along his ikkyo line as he does it.

It may seem simpler to assume a linear input is the cause of a linear result, but it is a fallacious assumption. Merely observing a linear resulting motion does not answer the question. (And please note again the internal rotation imparted to uke in his fall.)

You have not addressed the question of the nature of the kinetic input that resulted in that observed linear motion. You made a simplifying assumption, but it does not foreclose the rotational proposition, which is not really mechanically more complex at all. and it does not answer certain other observations that the rotational answer would predict and that is shown in the example. You propose a linear push in opposition -- I see in the video four distinct sets of "Connect, turn, enter and release." in two different axes of rotation in the nage waza -- all of which I describe in terms of rotational mechanics, but in that plainer language "Connect, turn, enter and release" is very much traditional tenkan-irimi movement of basic kokyu nage.

The only arguably linear element present is the final irimi lean of the thigh which simply maintains the input connection (ki musubi) to fully transmit the constant moment of rotation throughout uke's entire kuzushi movement (constant force, over time = acceleration). Even that is strongly modulated by the hip turn that allows the wieght shift to occur.
Quote:
Mike Sigman wrote:
The "spring constant" has a lot to do with why we train using breathing techniques and exercises like fune kogi undo.
I don't think fune kogi/funatori/torifune or what ever term is preferred in your neck of the woods, does what you think that it does.

The linear motion you ascribe to that exercise, is not really linear, but a pendular rotation of the torso in the A/P axis. As I was taught the exercise, the hips pivot over the legs about a fixed point on the ground, but the legs compress toward the middle and extend toward at the front and rear, forming an inverted arc of your CG travel.

In the funatori or funekogi exercise the center describes a downward arc from the rear limit to the center of your stance then rising toward the forward limit. Your shoulder girdle forms the axis of swing, and it oscillates back and forth over the the hip center to provide the initiating instability impulse to each swing of to the pendulum. In a proper irimi you essentially just fall into uke as you recover your own balance, like skier just falls down the hill.

This is BTW, the very same reciprocal teetering motion is seen in the video, well before uke's projection backward. I just was avoiding any term so obviously loaded with assumptions.

If you really are doing it laterally, without any vertical arc component, then the only momentum energy you get (even if you could store it in your legs and hip strain) is what lateral linear intertia your muscles can generate, which is 1) not free like gravitational potential, and 2) not as great in kinetic potential as the angular momentum as you can create by rotation and manipulation of radius of turn. An ice skater, uses this to great effect.

In essence, aikido irimi-tenkan is doing the same thing -- creating rotation in the balance system and then gathering in the balance to the center by a centripetal moment, caused by the inertia of the weighted foot with the ground (the crossing of the roughly figure eight path of the balance center) drawing that balance center (your oscillating mid-section mass damper (also known as the Angular Sweep Servo ) into the smallest radius manageable. Angular velocity increases proportional to the radius of turn. Kinetic energy is the square of the velocity.

My funatori motion is comfortably about 25 cm, and my feet are placed laterally about shoulder width apart , approximately the same distance. That is close to what I see O-Sensei moving in the thigh push.

Assume that the initial radius of turn is about half that (Tangent circle) or 12 cm, and that the radius of the balance sweep is brought into to it normal quiet stance excursion radius (see the study I cited and linked) of about 1 cm. The energy of shifting my mass 25 cm , plus the transformed energy of the weight drop that I put into initiating the radial acceleration of the turn, commences the turn. The reduction in radius of rotation inward increases the velocity of the balance center about 12 fold, and since the kinetic energy is the square of the velocity but only proportional to mass, this magnifies the effective energy for work about 144 times.

If my control is as precise as possible (and let us assume O-Sensei's was in the video), then the resulting kinetic energy when released into uke is thus: If you look at the diagram on normal balance center excursions that I cited, you will see that the balance center it can also manage intermittent periodic oscillation of about 0.25 cm diameter or 0.125 cm in radius. This increases the veloocity in inverse proportion to the reduction in radius : 12 / 0.125 = 96 times. The kinetic energy is the square of that veloicty -- on the order of 96*96 = 9216 times the effective energy for work.

All of this efficiency is obtained by obeying ordinary conservation laws.

Show me spring constants with that degree of energy conversion potential.

This funatori is a gain in kinetic energy from the fall energy. You ascribe that to a "spring constant" in your legs and hip undercarriage, but since you rise at the end of that motion, whatever "spring constant" of stored compression strain there may have been is dissipated.

Funatori is exercise in coordinated energy management (on which I think we agree), we just disagree on the energy being managed. It is not technique for application.

In applied technique, the only "storage" of this kinetically captured gravitation potential energy is its successive transformation by the rotational lift of your center and then precessional capture in the turning motion that comes at the end of the irimi movement as the center is rising on the second limb of the arc. No "linear" irimi or fune kogi motion in a technique occurs without a tenkan either preceding it or following it, which the video clearly shows - twice.

The process is reversible, which is the point of the tai no henko exercise, irimi energy is transformed into tenkan. Tai no henko is the mirror image of funatori in terms of energy dynamics.

Mere rotation is sufficent to avoid a strike, but is not sufficient to apply aiki technique, as any rotation that engaged uke's attacking moment in the same plane would directly oppose uke's energy in at least one component of those two axes. The transformation of that rotation by precessional means, moves the energy to a secondary rotation, in the same basic way as the irimi energy is captured in tenkan, or tenkan energy captured in irimi. The rotationally transformed moment energy is now applied where it is not opposed by any component of the angular moment of the attack -- on the two coordinate planes intersecting the torque axis of the attack.

Juji 3D.

Cordially,

Erick Mead
一隻狗可久里馬房但他也不是馬的.
  Reply With Quote