Unbalancing
Balance and unbalancing is an advanced topic. The principles require
an abstract understanding of momentum and inertia, as well as the motive
and structural support of an extended body. This can be studied as theory,
but is only effective if trained - as a lot of skills are involved.
Centre of Gravity
The key sensing principle in unbalancing is to detect and follow
the opponent's centre of gravity (COG), and its movement. For a motionless
body, the COG of a straight standing person is about two or three inches
above
the navel and inside the body, however, the opponent is normally
not straight standing - at the very least, their legs are bent somewhat.
In a front stance, crouch, or low back stance, the COG
is at about the location of the (lower) dan jun - ie, about two inches
below the navel. The front/back location varies a lot with leg position.
In Motion
In motion, the aggregate motion of the person may be considered as the
movement of the COG, although the limb (leg, usually) applying the main
motive force can often be ignored in this context - it is more of a 'part
of the ground', than of the person.
Gravity and Upward Reaction
Both limbs (legs) are applying vertical forces to resist gravity, and also may
(almost always do) apply horizontal forces and torques
which are partly mutually cancelled out, and partly produce
motion. To accelerate the body,
the main force acting on the COG comes from a push by the
foot/leg, from behind the COG. To decelerate, the main push is
from in front. The other foot
can pull to supply additional force, but this is always secondary.
The same applies to turning and spinning - where a net torque results.
The body will remain at
rest or in constant linear motion unless a force is applied
Non-rigid Bodies
Since the body is not rigid, different parts move with constrained
relative motion. The constraints come from the rigidity of the bones,
external forces, and intentional forces applied by the body's muscles.
Some forces will mainly re-arrange the alignment of the body, while
others will act on the COG.
Two Bodies
Interactions between two bodies, are best understood in terms
of the centre line between the bodies - ie, the line directly
between the COGs. Forces along this line are maximally effective
on the COG of the recipient. Forces delivered from above the line
(or downwards from below) are also pretty effective, but will tend
to squash downwards (or pull upwards) the recipient. Any force off-line
to the side will tend to spin or tip the recipient as well as move them.
Spinning and tipping are less useful in the self-defence context.
Likewise, the person delivering the force will receive minimal recoil
if their push is delivered from their COG,
and with the COG braced straight into
the ground (ie, using the reaction of the ground). Any force delivered
from off-line, to the side, will tend to spin the pusher - which can
be corrected dynamically via a set-up movement (go initially the opposite
way to which you expect to be counter-reacting), or which can be
corrected by a re-location of the COG (eg, lean), or some reactions
through the legs with the ground.
Essentially, the opponents are experiencing a two-body collision. If one
is highly skilled, the collision will maximally upset the other person,
with virtually no effect on the pusher. For a highly skilled person,
a push can be accepted without much effect - a combination of using rooting
and re-bounding to repulse the pusher. This requires good timing (and sensing),
and a fairly relaxed and alert body - at extremis, the counter-reaction is
of the same size as the pusher's effort, just smarter, better aligned, and
a little more sudden.
Training
This is tricky to understand as physics theory, but can be readily
learnt by the body. Simply work with a co-operative partner - trying
repeatedly to move them with gentle pushes. Learn the effect of smaller
pushes - the big ones will be trivial to understand in comparison. Then
try to turn the person by pushing off-line, but without a counter re-action
in your body.
Other practice includes pushing fixed object (like trees), 'testing' where
the receiver of the push sometimes stops resisting (so as not to learn
over-stepping), accepting and reversing pushes, push with follow-up footwork.
Importantly, don't lean.
Leverage
Lastly, you can apply a synthetic force, by simultaneously applying forces
and torques from more than one contact point. This may be the use of both
hands, or may include a pivot like a leg, hip or shoulder - judo style
unforced throws and reaps work, in part, in this way (see
throwing for the other factors in throws).
Throws resulting from
controlling
joints apply the leverage much more finely, and rely on angles of joints
- angles which the joints cannot exceed without much pain and damage.
These skills are also part of the techniques of throwing and restraining.
Here I wish to emphasise the momentum and interia aspects, rather than
the leading and controlling aspects. A good bump can often get
you out of trouble and also give unexpected opportunities.
Train hard. Train smart.
Tom Osborn - March 22 1996