Robert John wrote:
Well ok taking this a step further,
say someone takes the pushout posture, only instead of pushing the partner, he "punches" him. How does the angular momentum you describe keep the "puncher" from being knocked back, and why would the "punched" person be knocked back instead?
Remember the person is weakest physically front to back.
Maai and centering. The punching movement is critically delivered to maximize impulse with the inertia of the body driving the arm like a nail. There is very little room for error.
At impact (when they all four come on line) the puncher is pushing a stick with four joints in it (you count the clavicle/scapula separate from the shoulder orbit).
Just a moment before impact the clavicle/scapula is still out of line (eccentric) with the line of the other three joints, because it is rotating to drive the arm forward. Uke intended to meet static interia with all four joints in line in linear compression. Instead, his arm becomes the conduit of the offset angular momentum of the rocking forward inertia couple with his opposing forward inertia.
His arm now forms the connection of a horizontal inertial couple with the pivot at his shoulder, instead of at his opposing hip. The reversal of eccentricity causes a vertical couple between that the punching shoulder and the opposing hip, rotating his torso more or less vertically backward at the top. Since his hips are busy rotating forward at the time, he is likely to go outside his recoverable balance sway almost instantaneously.
Centering is a very small drop of the center as contact is made. This is naturally done to avoid over centering on the toes with the forward sway . This imparts a slight downwrad rotation of the arm with the shoulder, creating the same sort of couple in the vertical plane. This ecccentririty causes the clavicle/scapula joint to rise as the arm ortate in the vertical plane
This adds even more moment arm length and energy to the existing vertical toppling rotation. That vertical toppling rotation was caused by the horizontal rotation created by the offset impact, and that horizontal rotation offset was created by the original vertical rotation forward.
This punching example nicely of ilulstrates how the rotations transform and effects cascade on different axes in complement
All from tottering forward -- delicately.