---
name: ferret-physics-strength
description: Use to make things break in Ferret: bodies that take impact damage and split into pieces, joints that snap at the force their material holds, pre-fractured walls, the piece budget and replication of breaks by seed. Values toughness, threshold, pieces, burst.
---

# Strength and breaking

## When to use
A crate that breaks at speed, a rope or rod with a rating, a wall that falls in designed pieces, debris limits.

## The model
Damage is the **impulse above a threshold**: a gentle brush does nothing, a hard hit breaks the body into pieces (capped by the tier's `maxPieces`). `cap.joint({ type: 'rod', a, b, maxForce })` breaks at a force. The default `toughness` is infinite: nothing breaks until you set it. Events: `physics:break`, `physics:joint-break`.

## Steps
1. Enable `strength`; set `toughness` (N·s absorbed), `threshold`, `pieces`, `burst` at world, level, zone or entity scope.
2. Per-kind toughness: `config('strength').set('entity', 'toughness', 3, 'glass-pane')`.
3. Joints: `cap.joint(...)` after enabling; listen for `physics:joint-break`.
4. Designed pieces: `fractured` in the level's `physics` block (`edit.physics.fracture.set`).
5. Multiplayer: pass the owner's `BreakEvent.seed` to `breakNow` on remote copies.

## Check afterwards
A 3 N·s hit leaves a 10 N·s crate whole and a 20 N·s hit breaks it in the number of pieces set; two parallel rods fail weakest first.

## What usually goes wrong
- Nothing breaks: toughness still infinite at that scope.
- Breaks from a touch: `threshold` 0 so resting contact accumulates.
- Break event but no pieces: `pieces` 0, `maxPieces` used up, or (light kernel) the body is not a sphere.
- Load design: two rods share a load; the weaker goes and the stronger inherits it (`recipes/progressive-collapse.md`).

## Files

- `reference/strength.md` — Bodies that take damage from hard hits and break into pieces, links that break at the force their material holds, pre-fractured walls, the piece budget and replication by seed.
- `reference/api-physics-strength.md` — every export of `@ferret/physics-strength` with signature and doc comment
- `reference/commands.md` — 2 commands of these packages with their arguments
- `recipes/structures-and-ropes.md` — Six recipes: a rope that holds a load or snaps, a shear pin that protects the rest, a crate that breaks only at speed, a bungee that springs back, a wall that breaks under a blast, a curtain that hangs.
- `recipes/progressive-collapse.md` — Two parallel hangers share a load. When the weaker one goes the stronger one inherits all of it and fails too: progressive collapse, with redundancy as the cure.