Skill: write-like-james @ b0fa825 · the build: write-lesson, write-mcqs, write-video-script, review-lesson (two blind reads and a re-read), review-figures, review-accuracy @ b0fa825
Topic 1 "Why sliding things stop" — your read (2 October 2026)
Skim first
The lessons in teaching order, each with its one rule sentence; then the intro script; then the question types. The review page follows.
The lessons and their rules
| Lesson | Atom | Rule sentence |
|---|---|---|
| L01 Spot the friction | FOR4-001 | Two surfaces rub. A force pushes against the sliding. That force is called friction. |
| L02 Why sliding things stop | FOR4-002 | A moving thing does not stop by itself. Friction pushes against the sliding thing. So the sliding thing slows down and stops. |
| L03 Which surface lets it slide farther? | FOR4-003 | A smoother surface has less friction. So the same thing slides farther on it. |
| L04 Helpful friction, unhelpful friction | FOR4-005 | Helpful when you want the grip. Helpful when you want the slowing. Unhelpful when you want the sliding. |
The intro script (101 words, about 50 s)
Here's Elena on a winter morning, with her sled on the grass by the park gate. She pulls hard, but the sled hardly moves. Then she reaches the snow. The same sled glides on and on, and she has to run to keep up. The sled is the same, and Elena is the same. So what is different about the snow and the grass? To find out, we will see what happens where a sled rubs the ground, why moving things stop, and which surfaces let things slide farther. Okay, so are you ready to find out why sliding things stop?
The question types (from TYPES_G4T01.md)
- Type 1: Where does friction act (or where do two surfaces rub): a described scene; four places, one the rubbing contact, one "nowhere" (true only when the thing touches nothing).
- Type 2: Name the force: a definition or a rubbing scene; four force words (weight, friction, a pull, speed); hard form — type the name from the definition, the stopping rule, or a chain of scenes.
- Type 3: In which direction does friction push: the sliding direction stated; four directions.
- Type 4: What stopped it / what happens next: a thing let go of; four causes, or four outcomes.
- Type 5: Why it keeps going / why it stopped: reasons as options; the FOR-01 ("ran out") and FOR-02 ("something must still push it") corrections among them; a claim with the verdict fixed.
- Type 6: Which surface: farthest, most friction, sooner, or more friction than a named surface, from four options after the same push; distances as evidence of friction; hard — four distances to order, or four surfaces against a fifth.
- Type 7: The reason for a distance difference, or a change that would lower friction: FOR-12 ("pushed harder") as a distractor; hard — the FOR-12 claim judged by its reason.
- Type 8: Helpful or unhelpful: four scenes, pick the odd one; who wants more friction. (v2: the sort is never typed — a typed verdict is an MCQ in disguise.)
- Type 9: Why friction helps here (the grip or the slowing wanted), what a change did to the friction, or which change would help where the sliding is wanted; a claim about friction judged by its reason (FOR-08).
- Type 10: Select the set (multi-select). Retired in v2: both set items were split into single-answer MCQs (PP-47; the helpful-places set cut), so the bank holds no multi-select.
Grade 4's first topic, and the first built with no blueprint gate. Four lessons: where two surfaces rub there is a force against the sliding, called friction; a sliding or rolling thing stops because friction pushes against it, not because its push runs out; a smoother surface has less friction, so the same thing slides farther; friction is helpful when you want the grip or the slowing, and unhelpful when you want the sliding. Every key has been agreed by two cold readers and every changed item re-read; a non-author figure review and a guidance-and-accuracy review are applied. Pictures of real things and children are placeholders until you answer question 1.
The two that unblock the videos and the pictures
1. Does the friction arrow's tail sit at the rubbing surface, or at the object's centre as Grade 3 draws every force?
Grade 3's register puts a force arrow's tail at the centre of the object the force acts on. Friction's atom is about WHERE the force acts: where the two surfaces rub.
The drawings put the tail at the contact, pointing against the sliding, with a glow on the rubbing surfaces. One line in the register would record friction as the one exception.
Recommendation: at the rubbing surface, for friction only.
At the surface / at the object's centre
2. Does Grade 4's first video batch go to the Peps pipeline now?
Six videos: the topic intro, four lessons (L04 is marked "could do without a video"; it is scripted) and the summary. The batch is built and passes the brief checker. The Physics opening video ("Before we start") goes in the strand-intro batch, as Grade 3's did. Your rule from Grade 3 says your script review is the cue, and this is the first Grade 4 batch, so I am asking once.
Recommendation: send all six.
Send all six / send without L04 / wait
The lessons
3. L01 Spot the friction — Elena pushes a box of books across the classroom floor; it is hard work, and when she stops pushing the box slides a little and stops. Where the box's bottom rubs the floor, a force pushes against the sliding: friction. A thrown ball touches nothing, so no surfaces rub. page
4. L02 Why sliding things stop — Carmen rolls a ball across the grass and lets go; it slows and stops with nobody touching it. A moving thing does not stop by itself: friction where the ball rubs the grass pushed against the rolling. The ball did not run out of push. On the smooth hall floor the same ball rolls much farther. page
5. L03 Which surface lets it slide farther? — Darnell gives a toy car the same push on the wooden floor and on the carpet. The carpet is rough, so there is more friction and the car stops sooner; the wood is smooth, so there is less friction and the same push takes the car farther. More friction means a stronger push against the sliding. page
6. L04 Helpful friction, unhelpful friction — Reed's foot slides out from under him on an icy path; on the dry path his shoe grips. Friction under the shoe lets him push off; in a squeaky hinge it is unhelpful; a bike brake and a match use it to slow and to light. Friction is the same force in every case. page
Applied without asking
Your rulings in force: no blueprint gate (Topics 1 to 3 keep the blueprints already written); summary video before the mixed practice; "friction" recognised before it is typed; the three Grade 3 retrieval items in the practice (a push or pull can stop things; balanced forces; a stronger push makes a bigger change); the air left out, named once as a simplification; airborne cases ask "do two surfaces rub?"; the reviewer's L04 rule change ("the grip or the slowing", because the brake and the match slide); the bank at 50 items, 14 / 11 / 13 / 12 per atom, every hard item carrying its "hard because"; photo and cartoon placeholders with briefs for David's pack (12), svg by code for everything exact.
Also on the site
Topic intro and poll · summary and three questions · mixed practice · the PP100 bank · the blueprint · the type sheet
After you answer
1 → nothing changes on the page either way (the drawings are built as recommended; "centre" means one helper function and a re-render of seven figures), and the picture pass starts. 2 → the batch goes the same turn (the opening video with it); after this one, every Grade 4 topic's batch goes the turn its text is clean, as your rule says.