Physical science, as it developed in the west, revolves around what can be compounded out of a few basic units, primarily mass, time, and distance. Velocity, for example, is simply distance divided by time (meters/second), and momentum is velocity multiplied by mass (kilograms*meters/second).
This approach became far more powerful with the advent of calculus, which addressed rates of change (differentiation) and accumulation (integration). Differentiation and integration are complimentary concepts.
It was through his invention of calculus that Newton was able to arrive at a theory of gravity (that the attraction between two objects varies proportionally to the inverse of the square of the distance between them, 1/r-squared), and combine that with momentum to determine that the planets trace out ellipses as they orbit the sun.
If you have a mathematical expression describing the position (in a single dimension) of an object over time, then velocity is the change in that position over time, and acceleration is the change in velocity over time. Another way of saying this is that velocity is the first derivative of position, and acceleration is the second. Actually computing the first derivative of the original expression will give you a new one which describes the instantaneous velocity of the object at any moment, and computing the first derivative of that will produce one that describes the instantaneous rate of change in that velocity at any moment, or the acceleration.
This first derivative of acceleration, which is to say the expression describing the instantaneous rate of change in acceleration, is variously referred to as jerk, jolt, surge, and lurch.
At this point I'm going to switch from physics to biology, to suggest that jerk is closely related to the effect produced by the firing of neurons to activate skeletal muscles. A single impulse produces a spasm, but little actual movement, whereas an escalating stream of impulses produces a progressive tightening of the muscle, accelerating whatever movement the muscle generates.
But the bodies of higher organisms can't operate through the activation of a single muscle. They make use of cyclical patterns involving many muscles, each of which will alternately contract and relax as it plays its part in the pattern. These patterns are imprinted within and coordinated by the cerebellum, which presents a simpler interface to the rest of the brain.
When you want to raise your arm, you just raise your arm, without having to think about which muscles are pulling on their tendon connections to your skeleton to accomplish this. When you want to run, you may think "left-right-left-right" and/or "faster, faster", but again you're not having to consciously juggle the hundreds or thousands of impulses per second that initiate and sustain the pattern; that's all being done automatically for you by your cerebellum.
The first time you do something new, you're likely to do it very slowly and deliberately, because your cerebellum can only estimate what pattern will work for the new action and your conscious mind is more directly involved to make sure that it stays on track. As the cerebellum gains experience, the conscious mind can safely leave the details to it and simply choose to perform or not perform the action, as well as when, in what direction, and how vigorously.
If you collect a sufficiently complete repertoire of available actions, that your cerebellum knows how to perform, you may find that you are able to string them together in novel combinations, and even to create new actions on the fly, to tie those sequences together. This is partly a matter of the higher brain coming to trust the ‘black box’ of the cerebellum, and to understand how to guide it.
At this point, within the range of the repertoire, the question ceases to be what can you do and becomes what will you do? How will you use it? And your response to that question is your intention.
To get back to the point, I see chi as being the degree of alignment between that intention and the pattern of neural activations the cerebellum produces. Someone whose ‘chi is very strong’ has a high degree of alignment, which is to say that what they intend and what they do are one and the same.
While the concept ‘chi’ is tightly interwoven with physical movement, similar degrees of alignment pertain to the use of speech and the cultivation of emotion. These might be termed truthfulness and respect.
Not the conclusion you were expecting?