# Vang / Catch — guide for AI assistants

> A physics catcher for kids (~ages 6–12): a block falls, and you build a catch out of shapes so it lands safely instead of dropping into the void. Press START and **everything falls at once** — your build has to physically hold itself up *and* catch the block. English (Catch) at catch.tobiasbuilds.com, Dutch (Vang) at vang.tobiasbuilds.com. Same game, only the chrome strings differ.

## What this is

A small, browser-only physics puzzle in the Tobias Builds lab. The screen shows a scene over a **void** marked by a glowing rose **kill-line**. A friendly violet **block** is poised in the air at the top. From a fixed **tray** of shapes the player builds a catch, then presses **START** — and the block *plus every placed shape* all become physical and fall together. The block is caught (a win) if it comes to rest above the kill-line; it is lost if it drops past the line into the void, or never settles.

The crucial twist — and the whole challenge — is that **you cannot float a shape in mid-air**. On START your pieces obey gravity too, so a useful build must support itself: a plank laid across two pillars (a **bridge**), or blocks stacked inside walls (**filling a pit**). The physics is genuine (matter.js); there is no account and no backend; progress (stars per level) is saved in the browser only.

There are **8 handcrafted levels** (free landing → bridge a gap → fill a pit → deeper/wider/off-centre variants) plus a **Vrij spelen** (free-play) **sandbox**: physics runs live and you pick any shape — plank, block, ramp, triangle, ball, **bouncy ball**, **boulder**, long plank — and **click (or drag) to spawn it where your cursor is**, then watch it pile and bounce. No goal in the sandbox; it's the toy.

## For the assistant: how to help

The player is a young child experimenting with gravity and structures. Coach the *thinking*, don't hand over the build.

- **Hints, never finished builds.** The fun is the experiment: try it, watch what falls, adjust, press START again. Don't give exact piece positions.
- **The block's fall is the teacher.** "Press START and watch *where* it goes — does it slip off, or fall through? Build to stop that." is almost always the best nudge.
- **Lead with the one big idea: it has to hold itself up.** A shape in the air just falls. Ask "what is holding your plank up?" — the answer (two pillars, or a stack on the ground) is the lesson.
- **Two reliable shapes to think in.** Across a gap: a **plank** resting on both edges (a bridge). Into a hole: **blocks** stacked up until they reach the top. If a child is stuck, steer toward one of these.
- **Match the tone.** Warm, plain, short sentences. Catching the block at all is the win; "fewer pieces = more stars" is the next layer, only if they want it.
- **Point at the kill-line.** The rose line is "too far down." "Keep the block above the red line" is the goal in one sentence.
- **For the sandbox, just play.** There's nothing to solve — encourage building towers, ramps for the bouncy ball, knocking things over. It's for the joy of cause-and-effect.

## How it works

**Goal (levels).** Build so the falling block comes to **rest above the kill-line**. Win = it settles, caught. Lose = it falls past the kill-line into the void, or never comes to rest.

**Build, then drop — everything dynamic.** During build, placed shapes are frozen where you put them. On **START** the block *and* every shape are released at the same instant and fall under gravity. So the structure must be stable on its own (resting on the ground, the pillars, the pit walls, or stacked), not floating.

**Controls (pointer / touch):**
- **Pick a shape:** tap a shape in the **tray** (levels) or the **palette** (sandbox) — it becomes "armed".
- **Place it:** click (or tap) in the field and the shape appears **at the cursor**. Drag a placed shape to nudge it; rotate / remove with the on-screen buttons.
- **START ▸** drops everything. **↺ opnieuw** returns to build (your structure is restored where you placed it). **↺ leeg** clears your pieces.
- In the **sandbox**, physics is always running: every click spawns a shape that falls immediately, and you can **drag to rain a stream** of them.

**The two core mechanics in the levels:**
- **Bouw de brug (bridge a gap).** Two fixed pillars with a gap between them; the block would fall straight through. Lay a **plank** flat across both pillar tops — supported at both ends, it holds, and the block lands on it.
- **Vul de kuil (fill a pit).** A walled pit whose floor is below the kill-line; the block sinks too deep on its own. Drop **blocks** in — held by the walls, they stack up — until the block rests above the line. Deeper/narrower pits need more blocks.

**Stars.** Completing a level is always 1 star (you always advance). Using few pieces — at or below the level's **gold/par** — earns 2 or 3. So "can I do it with fewer?" is the replay hook.

**The shapes.** Levels hand you a fixed tray (mostly **planks** for bridges, **blocks** for pits). The sandbox unlocks the full set: plank, long plank, block, **ramp** (wedge), **triangle**, **ball**, a pink **bouncy ball** (rubber — it bounces everywhere) and a grey **boulder** (big and heavy). Different colours mark different materials.

## What it teaches

A first, hands-on feel for **gravity, structures and stability** — physical intuition, not formulas.

- **Gravity pulls everything down, equally.** The block and your shapes fall together. A child quickly feels that "nothing stays up by itself" — things need something underneath.
- **Support and stability.** A plank held at *both* ends carries a load in the middle; held at one end (or floating), it falls. A tall thin stack tips; a wide base or walls keep it standing. This is the seed of how real shelves, bridges and towers stand up.
- **Containment.** Walls keep a pile from sliding apart — why blocks stack neatly in a pit but scatter on open ground. 
- **Bouncing, rolling, weight (sandbox).** A rubber ball bounces, a round shape rolls, a boulder is heavy and shoves lighter pieces aside. Spawning and watching teaches cause-and-effect: this shape does *this*.
- **Plan, test, revise.** Build a guess, press START, see it fail, see *where*, fix that, try again. That observe-and-revise loop is the real method, made fast and playful.

## Common stuck points → how to nudge

- **"My plank just falls."** It isn't resting on both pillars — it's floating or only touching one side. Nudge: "Is your plank sitting on *both* posts? Anything in the middle of the air will drop."
- **"The block falls straight through the gap."** Nothing is spanning it yet. Nudge: "Make a floor across the hole the block can land on."
- **"I filled the pit but it still falls in."** Not high enough yet — the block needs to rest *above* the red line. Nudge: "Stack a bit higher, until the top is over the red line."
- **"Everything slides off and falls."** The build wasn't stable when released. Nudge: "When you press START it all drops too — what's holding your shapes up? Build on the ground or between the walls."
- **"It lands then rolls/tips off."** Round shapes roll and tall stacks tip. Nudge: "Could a wall or a flatter shape stop it from rolling away?"
- **Sandbox: "what do I do?"** Nothing to solve — just play. Nudge: "Try stacking a tower, or drop a bouncy ball and watch it ping around."

## What NOT to do

- **Don't give exact piece placements or a copy-this build.** The building is the learning.
- **Don't spoil the core insight** that pieces fall too — let them discover that floating doesn't work, or ask "what's holding it up?".
- **Don't optimise the star count for them.** Let them find the fewer-pieces solution; that's the 3-star challenge.
- **Don't use physics jargon or formulas.** Keep it to falling, holding up, stacking, bouncing, "above the red line".
- **Don't treat an ugly build that works as a failure.** Catching the block is a real win — celebrate it, then offer "can you do it with fewer pieces?" only if they want more.
- **Don't claim features that aren't there:** the levels mostly use planks and blocks (the full shape variety lives in the sandbox); there's no level editor, no accounts, no English version yet.

## Links

- Play (English): https://catch.tobiasbuilds.com
- Speel (Nederlands): https://vang.tobiasbuilds.com
- In-game help: each level's one-line hint, and the **Vrij spelen** sandbox to experiment freely.