By now (read the previous post Where is the Friction from the Floor? – Force Transfer on Scale and Mahjong Tile), I hope you can at least accept that it is possible to counteract a horizontal push by a vertical reactionary force without a horizontal friction from the floor. Let’s go further to see how forward momentum works.
Recall that the spectrum of force transfer reflects the different degrees of flexibility and capability of the body in controlling the amount of incoming force getting into the body. The more it allows, the more force will be transferred to vertical. While the less is allowed, a significant portion of the incoming force has to be expelled right at the contacts.
So far the role of the body mass (hence momentum) is relatively passive – it is in the receiving mode to entertain the incoming force. At this point, there is an important property prevailing in the structure – all joints are still free, as if they are “lubricated”, prone to move or to be moved in any direction, despite the fact that they are at the same time sustaining the structure processing the force transfer.
The point-linked structure, formed by the lubricated joints, starts to move forward (initiated by the lower body centre, tapping into the vertical reactionary force). Once set in motion on the horizontal, the body “floats” on the knee level (the post Counterintuitive Stance: Stacking vs Rooting; Floating vs Leaning), where the lubricated knee joints are so smooth that they don’t pull the vertical alignment back and thus don’t consume its momentum (energy); the momentum is best preserved. In this way, the body mass becomes the power source fuelling all movements on the horizontal (fighting and blocking by arms, kicking, as well as stepping), without drawing (frictional) support from the floor. Put it the other way: the body mass does not just appear as a weight due to gravity (downward), but is also fully turned into a power engine to “propel” limbs (forward).
How would the floating body mass react when the push increases? Recall again that the body structure can react in two ways: 1) allows the increase to go into the body and transfers it to vertical; 2) does not allow the increase to go into the body but expels it right away at the contacts by converging and microscopic deflection. You can imagine that in reality the body mass reacts in a combination of the two ways, seldom just one. You can allow its initial increase into the body to be transferred to vertical down to the pelvis and the knees (not necessarily to the feet) so that the pusher feels being stopped by a solid something, and your vertical alignment immediately floats (in small extent) to “propel” your hands to expel, with converging and microscopic deflection on, any further increase from the pusher. If the floating is abrupt, the pusher will even be suddenly sent backward due to the impact generated by the accelerated body mass.
But for the sake of discussion, let’s imagine the scenarios of just one each separately.
Force transfer only: This is basically the scale demo situation. The initial pushing force has been transferred to vertical to be borne by the feet (two feet on floor in reality). Any increase in the push will be completely transferred in the same manner, until the arms cannot take up any more. This is the limit (maximum force transfer), beyond which the body structure will break.
Expulsion at contacts only: The initial pushing force (of acceptable magnitude) has been allowed to go into the body and be transferred. Any (intended) increase will be completely expelled right away at the contacts. This seems to suggest that the amount of force allowed is always the same, i.e. the initial pushing force. In reality, the strong converging and microscopic deflection in play actually affect the pusher in return – his body (muscles) is more tensed up and more engaged as seen in holding (or pressing) tighter and tighter at the contacts with you. This could result in his support for a portion of your body weight (downward) through the “tight” contacts. The force he is trying to exert on you turns out to have helped carry a part of your body. You have become lighter! In effect, your body and the pusher’s have been bound (at the contacts) into one dynamic structure, in which your weight can be “shifted” to be borne by the pusher’s body (one-way) but at your discretion only.
The scale demo had been so well received that a number of us applauded the magic (increase in weight) in front of Grandmaster Chu. He responded with a smile: “I can give it back to you and make myself lighter.” All surprised!