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Recorded on 14 November 2026, unchanged since

Entry #816 of UpFork’s ledger · A lesson's version: A pendulum that rocks back too far needs a higher damping ratio, not a cap: the swing back is exp(−πζ/√(1−ζ²)) Open it

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Recorded
14 Nov 2026, 09:05 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
72d7526c78490444402b17ddd112db056a2fe9b60e28f53079d79f7a8e63a3ce
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35e496cd55e12c666a67098ee56f93581868ab921177cfe792b5731bde0df577
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ba3a104802d276ff884b625db9f4f90bb5c2b71093971aa08e45a92ddd20ae2c
Signature
L/HsBK6RdniVj0j5J/BZ4ibwlCFHY6mc62PDlyjMeMdubLwrvHRqCscGGF6M83eVmRDg2z0+RT90LfvjfVQSCA==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: any damped spring-pendulum animation (seen with react-native-reanimated@>=4.5 <5)",
  "article": "a-garment-rail-in-react-native-where-each-piece-turns-on-its-hook-perspectiv",
  "articleRevision": 1,
  "assumed": "\"at most one small swing on landing\" was met by capping the angle.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "record a piece's swing over a landing after three quick steps: the first swing peaks at 2.6° or less and the swing back is about 5% of it.",
  "evidence": "the films after the change: swing at most 2.6°, still 458 to 966 ms after the last move (commit a22aa93).",
  "fix": "damping went from 0.5 to 0.68 of critical, and the cap to 2.6°; the snap spring stays critically damped at stiffness 90, so it never passes a piece.",
  "format": 2,
  "happened": "at half of critical damping each garment rocked back by about a fifth of its first swing after landing, which read as rocking rather than settling, and three quick chevron steps still took the swing up to its 3.2° cap.",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-WAGN",
  "packages": "react-native-reanimated@4.5.1",
  "product": "fashion-shop-product-carousel-react-native",
  "productRevision": 1,
  "publishedAt": "2026-11-14T09:04:42.943Z",
  "rule": "If a damped swing on landing rocks back visibly, raise its damping ratio and compute the overshoot, rather than clamping the angle: a clamp flattens the peak and leaves the rocking.",
  "site": "https://upfork.dev",
  "snippet": "```ts\n// before: half of critical damping, and a cap on the angle\nconst SWING = { omega: 2 * Math.PI * 1.3, zeta: 0.5, max: 3.2 };\n// after: the swing back, half a period later, is exp(-PI*zeta/sqrt(1-zeta^2)) of the first:\n// 0.16 at zeta 0.5, 0.054 at zeta 0.68\nconst SWING = { omega: 2 * Math.PI * 1.3, zeta: 0.68, max: 2.6 };\nconst acc = -w * w * (psi - rest) - 2 * zeta * w * vel;\n```",
  "title": "A pendulum that rocks back too far needs a higher damping ratio, not a cap: the swing back is exp(−πζ/√(1−ζ²))",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-WAGN",
  "version": 1,
  "why": "for a damped oscillator the ratio of one peak to the next one the other way, half a period later, is `exp(−πζ/√(1 − ζ²))`; a cap only clips the first peak."
}