The governing principle from which all other fidelity criteria follow.
The first-principles requirement that establishes whether a simulation system can produce valid outputs at all. If motion does not originate from physics, no downstream fidelity criterion can be met.
Physics First: Simulation must be governed by real-time physical modeling of the system being represented. Motion, response, and feedback must originate from the underlying physics rather than from post-processed effects, approximations, or cosmetic movement.
Failure Consequence: If physics is not the source of motion, the system cannot reproduce correct behavior, regardless of how active, immersive, or visually convincing it appears.
In the real world, every vehicle behavior is a consequence of physical law. Torque, mass, inertia, friction, and aerodynamic load interact continuously to produce motion. No approximation of that output can substitute for the process that generates it.
A system that generates motion from post-processed effects or scripted responses will always produce outputs that are:
Physics First is the source layer. All downstream criteria (independent degrees of freedom, center-of-mass origin, temporal synchronization) are structural consequences of physics-governed motion. They cannot be met by a system that does not begin here.
A simulator may appear to move through three axes, produce visual changes, audio feedback, and physical displacement. None of these outputs establish that it operates from physics.
The structural test is not whether a system produces observable movement. The test is whether that movement originates from a mathematically valid model of the forces acting on the simulated system. If the motion source is an effect library, a tuning profile, or a motion-cueing algorithm applied over disconnected visuals, the Physics First criterion is not met.
Systems that approximate physics at the output layer cannot recover structural validity. The error is introduced at the source, before any cue is generated.
Observable motion does not confirm physical origin.
Motion is detected before visual confirmation. The vestibular system registers rotation at the center of mass before the eyes can report a change in heading. This sequence is not incidental. It is the order in which the physical world delivers information to the nervous system.
A simulator that cannot reproduce this sequence cannot train the perceptual responses that depend on it. Physics-governed motion is the only mechanism by which the correct timing relationship between felt motion and observed motion can be preserved.
The perceptual consequences of this sequence are examined in full on the yaw in simulation page.
Physics First establishes the source requirement. The next criteria define the structural consequences of physics-governed motion.