Ignatius Teo wrote:
Hmmm... Newton's 3rd Law... Every action has an equal and opposite reaction. EQUAL AND OPPOSITE. If you push on a wall with 500N of force, how much force is acting on you?
The same -- because the wall pushes back as you suggest. That is not the only means to balance forces, however. I rely on the Second Law to balance the force equation, not with force against force, but allowing his force to accelerate my inertial mass about my center. Second Law : F=ma. That's what he wanted to do -- induce (severe) accceleration in my body. So I allow him to do that, but not the way he envisioned. I can manipulate my inertial moment (how much force is required to induce a given angle of turn) by altering my structure -- without exerting any opposing force.
Someone pushes on me, I don't push back -- I place myself so as to allow myself to be accelerated (in the "right" way) -- around my center (tenkan) I typically arrange my structure to increase or decrease my inertial moment as needed and to alter the eccentricity of that acceleration to cause some manner of entry (irimi).
If I accept the force and convert it to some component of angular velocity, it ultimately returns (opposite) to him what sent it -- without me having to add energy to or detract from it or to move my position laterally at all, or even being moved by him, seemingly, contradictory to his intent (irimi).
Ignatius Teo wrote:
If you push on someone using the same amount of force, and they stand like an inanimate object grounding the force, how much force is acting on you? ... Where is the resistance?
500N -- from two directions You are experiencing 500 N of force from the push and the inverse vector (in some component) of 500 N from the ground, net zero force, but not net zero displacement. You are experiencing compressive (crushing) stress or strain (deformation energy) in between the two, and are the conduit for both. Material stress or strain energy is not the same thing as inertia.
You are acting as horsehoe to the hammer of the blow and the anvil of the ground. You are communicating the resistance of the ground to the force of the blow - and you deform (strain energy) according to the limits of your structure. You are primarily limited by the strength of your structure in that interaction.
Conversely, receiving forces tangentially allows me to accept absolute forces of much greater magnitude, because I can control how firm my perpendicular connection is and thus how much of that energy I accept at the point of connection and convert by irimi/tenkan principles and how much of it I let pass by to conserve his momentum to use and guide back to him. I am not primarily limited in that interaction by my strength of structure (as long as I can hold myself
together), but by my level of control.
The thing about overt movement in this mode is that if I accept tangential energy in the form of angular momentum at a large inertial radius (extension), I reduce its perceived kinetic energy at the connection. If deliver that angular momentum back at a far smaller radius, I exponentially (two cumulative square terms) increase the effective kinetic energy at the point of the return connection. "Movement in stillness," i.e. -- virtually zero radius of the return moment becomes nearly infinite (mathematically) and devastating, practically (think about the skater toe-spin).