How about the mass the screwjack is sitting on, though? I.e., in the transfer of forces to the car, the solid connection to the earth plays a role in the mass x acceleration component of the force equation. The mass of the earth is considerable. If you are "straightening out" a force that derives its support from the earth, let's say a punch for example, it affects the whole perspective of F = ma and brings into play some applicable thoughts about Impulse and momentum.
No one said it didn't. The mass the screwjack is sitting on (the earth) is moving, but so is everything else in this relative frame of reference. Relative momentum between the car, the earth, the jack and the driving motor or body is initially zero. The crank is turned by the oscillating driving of the inverted pendulum of the COM about its point of support on the ground. Even kneeling down by the tire wheel the torso has to oscillate as the arm turns the crank to turn the screw to raise the jack, ("which lay in the house that Jack built"). If the body oscillates as a resting reactive mass, the arm will wear out from fatigue because it is doing most of the work pushing on the body as much as it pushes on the crank -- if it oscillates as a tuned driving mass -- the arm muscles are not doing the bulk of the work, and the same impulse that is created in driving the crank, can drive the punch, and is seen in funetori undo, saya undo, ude furi, furitama, tekubifuri. The nature of this oscillating action is, as I comprehend the term, "KI."
The earth is large enough to be both a resting reactive mass (thrust base) and a passive driving mass (gravity), and thinking about those aspects in this way is entirely correct, but they are a special case of a more general principle. If I thrust at the earth to punch, and I miss -- I am launching my own mass off the ground (kuzushi). If I use an mechanically amplified oscillation, pivoting with gravity on that support and recovering with the earht's reactive mass rather than projecting thrust from it, I can more easily stop the action most anywhere at zero. The magnitude of the energy is derived from the difference in potential in separating the positive and negative phases of it. As long as keep them separated I create large magnitude action or potential action and as soon as I bring them together again they inherently restore a zero state. Sword work, working on precision in point, path and placement in strikes thrusts and nagashi in kumitachi, teaches this principle implicitly.