Topic Brief: Moments Rods on Two Pivots

Provenance: written 2026-09-29. Primary source: research/veridian/WME01-verified-facts.md §1 (spec text), §4 topic 6 "Moments," §6 and §9's moments-lesson audit entry (lines 224–232) — searched and re-read for this topic this session. Cross-checked against content/veridian/curriculum/wme01/moments-rods-on-two-pivots.ts (read in full, so this brief does not repeat its worked chain, diagram, or marked-solution), content/veridian/technique-hub/wme01/codex-deep-dive-moments-rods-on-two-pivots.md (read in full — its §1 model, §2 sub-case catalogue A–E, and §4 synthesis table are the per-case mechanism and worked detail; this brief does a different, narrower job, described below), content/veridian/technique-hub/wme01/forge-exam-technique-guide.md (read, for the two real mark-by-mark tables covering Jan 2025 and Jun 2025 in full), content/veridian/technique-hub/wme01/signal-frequency-and-boundaries.md (read, for its own topic-frequency line on 6.1), and content/veridian/question-bank/wme01.ts (grepped for "moment/pivot/tilt" — no hits, nothing to cross-check there). No new primary-source PDF was fetched for this pass.

#SIGNAL Topic Master Brief · Moments — Rods on Two Pivots

#WME01 (Mechanics 1), spec item 6.1

What this document is for, and what it isn't. CODEX's deep-dive already builds the physical model and works through five named sub-cases (A–E) with real numbers where the archive allows it. This brief doesn't re-derive any of that. It answers a narrower, different question: across every series this course has actually checked, how often has this topic shown up, at what mark weight, in what paper position, and under what recurring angle — the roll-up a student revising the topic actually wants, not the method.

#1. Every real series confirmed testing this topic

Confirmed in 6 of the 17 series this course has reviewed a genuine primary source for:

• Jan 2020, Q2 — rod held by two tensions (not resting on supports); a misread "20 N more than" relationship between the two tensions.
• Jan 2023, Q4 — non-uniform rod, weight W and centre-of-mass position x both unknown, solved from two separate "about to tilt" conditions.
• Jun 2024, Q4 — uniform rod on two supports; efficient pivot choice explicitly rewarded by the mark scheme.
• Oct 2023, Q1 — pivot choice confirmed as an efficiency point independently of the tilting-trap wording above.
• Jan 2025, Q4 (10 marks) — multi-part question; a support's tension and an attached particle from an earlier part wrongly carried forward into a later "point of tilting" condition.
• Jun 2025, Q5 (6 marks) — tagged only as "a rod carrying several unknown forces at once"; not deep-mined beyond that tag.

That is 6 named series out of 17, not 6 of some larger unchecked total — the other 11 simply were never mined topic-by-topic for this spec point one way or the other.

#2. The real mark-tariff pattern

Only two series have a captured, real mark total for their moments question, because only Jan 2025 and Jun 2025 were mark-mapped question-by-question in full: Jan 2025 Q4 = 10 of 75 marks (≈12 minutes at the paper's own 1.2-min-per-mark rate); Jun 2025 Q5 = 6 of 75 marks (≈7.2 minutes). No single mark total for the Jan 2023, Jun 2024, Oct 2023, or Jan 2020 moments questions was captured as a number anywhere in this course's own research, so none is invented here — 2 of 6 series checked this way, not 6.

Paper position is the more consistent finding. Across the 6 confirmed instances, the question number is Q1 (Oct 2023, of 7 questions), Q2 (Jan 2020), Q4 (Jan 2023, Jun 2024, and Jan 2025, each out of 7 or 8), and Q5 (Jun 2025, of 8). In none of the 6 is it the paper's final question, and in 5 of 6 it sits in the middle third of the paper rather than opening it. This is a real contrast with spec item 4.2 (connected particles/pulleys), which this course's own FORGE and SIGNAL documents confirm sits last and heaviest in both fully mapped series — moments does not show that pattern in any series checked.

#3. The recurring context/angle types, by count

• "About to tilt"/"point of tilting," with the efficient single-pivot method rewarded and a wrong-reaction-zeroed error penalised — 3 of 6 series (Jan 2023, Jun 2024, Oct 2023).
• The rod's own weight and centre-of-mass position both unknown, requiring two tilting conditions solved together — 1 of 6 series (Jan 2023 — the same series as above; it supplies both angles at once).
• Rod held up by tension(s) rather than resting on supports — 1 of 6 series (Jan 2020).
• A multi-part question where a force established earlier (a tension, an attached particle) must be dropped once a later part's physical scenario changes — 1 of 6 series (Jan 2025).
• Tagged only, no worked detail recovered — 1 of 6 series (Jun 2025).

No sub-angle above reaches this course's own 3-series bar for calling it a standing convention on its own; only the first (pivot-choice efficiency) does, and it already carries that status in CODEX and the lesson file.

#4. What the archive does not confirm

No series in this archive was found testing a plain rod-on-two-supports moments question with every quantity given and nothing to eliminate — every real instance found has at least one twist (a tilting condition, an unknown rod weight, tensions instead of reactions, or a stale carried-forward force). Whether that reflects how Pearson actually writes this question type, or simply which series this course has deep-mined, is not something the archive can settle — recorded here rather than guessed at.

#5. If this topic appears — what to expect

Expect a mid-paper question, not the paper's opener or its final, heaviest one — 5 of 6 confirmed instances sit in the paper's middle third. Expect it to cost roughly 6–10 marks where a real total exists (2 of 6 series), and budget accordingly rather than assuming a fixed weight. Expect a twist rather than a plain "find both reactions" ask: most likely an "about to tilt" condition naming one pivot (remember the zeroed reaction belongs to the other support), and — in a multi-part question — check every force named in an earlier part is still physically present before taking moments in a later one. Draw a diagram: January 2025's own report on this exact question states unsuccessful candidates "would have benefited by drawing diagrams."

#Sources

research/veridian/WME01-verified-facts.md §1, §4 (topic 6), §6, §9 (lines 224–232). content/veridian/technique-hub/wme01/codex-deep-dive-moments-rods-on-two-pivots.md §2, §4. content/veridian/technique-hub/wme01/forge-exam-technique-guide.md (Jan/Jun 2025 mark-by-mark tables, §1's diagram-advice quotation, and its Case-E-adjacent trap-digest entry). content/veridian/technique-hub/wme01/signal-frequency-and-boundaries.md §1. content/veridian/curriculum/wme01/moments-rods-on-two-pivots.ts (read in full; its worked chain and marked-solution are not repeated here). content/veridian/question-bank/wme01.ts (confirmed no existing item on this topic, so nothing to cross-check against).