Harry Leung (extract): …… I would appreciate if you could explain CST’s wing chun of COM (does it feels like a ball spinning inside our body?), generally on how it is developed and used and whether it is always spinning or spins it only when we want to execute a movement eg, liking walking? or does it feels like we are resting our body weight and centre point on the COM? What is the difference between COM and the centre of gravity of our body?
Scott Hooten (extract): …… In physics, COM is usually point in any mass (if I were in space and was set in rotation, the rotation center would be COM). Our center of rotation is the line going through our spine and tailbone to the ground and the one we turn on in Chum Kiu. From my limited understanding, the two become one in Biu Jee and the rotation is around the COM and capable of moving in all directions internally and externally with the internal driving the external ……
Me: Everyone has his/her own interpretation. I would approach it from my usual “point” model. However, it doesn‘t represent an authenticity of the CST lineage; just my personal opinion.
Following what I have been suggesting in the previous posts, the way of exploring the centre of mass (CoMass hereafter) is of no secret – start from soften-melting neighbouring muscles of each joint to free that joint, which in this way will gradually appear as just a point in your mind; connect them (those you can already figure out in your mind) in stable but light linkages. This is an ongoing and iterative process. There will be a moment when you can soften-melt deep enough to discover the lower centre point (described in the previous posts) and connect it with other points (vertebrae joints immediately upper and hip joints immediately lower). The linked point structure (connecting as many points already appearing in your mind as possible) now operates as one, being initiated by that lower centre point, which normally should be the CoMass.
A point acts by spinning. A preceding point spins its following point. Starting from the CoMass as the initiator point, every following point receives the spinning momentum from its upstream, and at the same time but independently spins itself – such momentum is being accumulated downstream and finally reflected on the limbs (arms and legs) and the head. But since the point is small, in fact should be tiny, it is dimensionless in the mind. Thus its spinning is instant at great acceleration but without elaborate movement outside (absence of rotational movement of an circular arc inside), and the spinning momentum effecting on the next point is accordingly instant too. In this way, the “accumulation” of spinning momentum up to the limbs doesn’t cause time lag. You can say: when an opponent presses your forearm, he is effectively and instantly pressing your CoMass direct, which can also effectively and instantly fight back direct with an “accumulated” spinning momentum from the entire linked point structure mastered by the CoMass. With this understanding, you can argue that there has been no “flowing” (say, from the CoMass) at all; everything is instant and direct.
Now I can try to answer your questions according to the above conception.
CoMass always spins. To it (as a tiny point), spinning doesn‘t necessarily manifest as observable movement. When your body looks at rest but in the Wing Chun state, every point is still spinning within the linked structure.
In my interpretation of Wing Chun, the CoMass doesn’t act as a ball, but a tiny point. And its own spinning doesn’t entail rotating a circular arc or an entire circle, as seen in the self-spinning of a ball. Acting like a ball might be something found in Tai Chi, I suppose.
There seems no need to further differentiating CoMass from centre of gravity for the purpose of explaining. Just treat them the same.
When starting practising Chum Kiu, the central axis (centre line of rotation) is more emphasised. This axis is virtual (not necessarily going through the entire spine and the tailbone) and is treated as one piece running vertical through the body, confining the pivoting of the body only on the horizontal plane. Normally, it does run through the CoMass. Conversely, the axis should be rotated via the CoMass (not necessarily point operation).
When practising Biu Jee, there should be no more one-piece axis, having been replaced by the linked point structure described above. Note that the virtual axis has no role here. Rather, the point-linked line running through the spine mimics the function of the virtual axis but enables instant spinning beyond the horizontal plane at any moment.