Physics model picker
Three inputs. The question you are asking, how accurate the answer must be, and a few dimensionless numbers. The page then names a model. It does not prove that every omitted effect is negligible.
What the sliders mean
| Criterion | What it answers | How to read it |
|---|---|---|
| v/c | Does this kinematic quantity need special relativity? | A representative low-speed correction is about ½(v/c)². The coefficient depends on the observable. |
| S/ℏ | Is a semiclassical trajectory still usable? | Useful for motion and collision estimates. It does not decide color, coherence, or quantum statistics. |
| Re | Which drag law? | Re ≪ 1 is the Stokes regime. Re < 1 is only the low-Reynolds side. Around 10³ and above, quadratic drag is the usual fit. Between them, use an empirical Cd(Re). |
| (v/vt)² | Does drag matter for this answer? | Compare drag with weight. A dust grain can have tiny Re and still be drag-dominated. |
| N | Do finite-sample fluctuations affect the answer? | A typical relative fluctuation is about 1/√N. Large N does not by itself rule out quantum degeneracy. |
| De | Does the material act like an elastic solid or a fluid on this timescale? | Only for collision and deformation. It does not by itself prove a rigid body. |
The live picker, including the Chinese recommendations, is the copy tied to the criteria engine.