Verified instrument · Tier 1 · 3D

Dzhanibekov Effect

Spin a body about each of its three principal axes: two spins are stable, the middle one flips over and over. Energy and angular momentum conserved to machine precision; the flip period is verified against the Jacobi-elliptic closed form.

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→ L angular momentum (world frame, fixed) · → ω angular velocity (tumbles)

What to notice

  1. Start on the intermediate axis: the body flips 180° at regular intervals with nothing touching it.
  2. Watch the L arrow: it never moves. Angular momentum is exactly conserved in the world frame while the body tumbles around it.
  3. Switch to the major or minor axis: same body, same conservation laws — but the spin stays locked. Stability is a property of the axis.
  4. Shrink the perturbation: flips become rarer (the period diverges as ε → 0). A perfectly aimed spin would never flip; perfection does not exist.

What "verified" means here

This instrument's physics kernel is covered by assertion classes V1, V2, V5, V6 run on every commit — and its aha-fact is itself a named test:

⚑ A body spun about its intermediate axis flips periodically while E and L stay perfectly conserved — stability belongs to the axis, not to the conservation laws.