roblox-physics git:20261015.f9f74c2A

Immutable. This exact content never changes and is served at /api/v1/blob/fe6f9a07e6520d78.

---
name: roblox-physics
description: "Use when building or fixing Roblox physics: vehicles, ragdolls, projectiles, elevators, constraints, forces, network ownership."
when_to_use: "Also when parts fling, jitter, fall through floors or desync, and when tuning projectile or knockback feel."
last_reviewed: 2026-10-14
sources:
  - https://devforum.roblox.com/t/cframe-operations-for-the-rest-of-us/3546477
  - https://raw.githubusercontent.com/Roblox/creator-docs/main/content/en-us/physics/mechanical-constraints.md
  - original
  - https://raw.githubusercontent.com/Roblox/creator-docs/main/content/en-us/reference/engine/classes/Humanoid.yaml
  - https://raw.githubusercontent.com/Roblox/creator-docs/main/content/en-us/reference/engine/classes/WorldRoot.yaml
---

# Roblox Physics

## When to Load

Use this skill when building physics-driven gameplay: vehicles, ragdolls, projectiles, mechanical contraptions, elevators, swinging platforms, or anything using constraints and forces.

## Quick Reference

### Constraint Types
**Mechanical:** `HingeConstraint`, `PrismaticConstraint`, `CylindricalConstraint`, `BallSocketConstraint`, `UniversalConstraint`, `WeldConstraint`/`RigidConstraint`
**Motion:** `AlignPosition`, `AlignOrientation`, `LinearVelocity`, `AngularVelocity`, `VectorForce`, `Torque`
**Spring/Rope:** `SpringConstraint`, `RopeConstraint`, `RodConstraint`

### Attachment Pattern
Constraints connect via `Attachment` objects. Create one on each part, set `Attachment0`/`Attachment1`, and parent the constraint to part0. Actuator types include `None`, `Motor`, and `Servo`.

### Vehicles
Vehicles: use motorized `HingeConstraint` wheels, `SpringConstraint` suspension, servo steering, and `CustomPhysicalProperties` for friction tuning.

### Ragdoll
Track the joints and instances each ragdoll changes; recover only owned state, and coordinate overlapping effects before restoring movement. `BallSocketConstraint` recipe: full.md.

### Authority and Network Ownership
Classic projects: automatic ownership can give an unanchored assembly to a nearby player. `SetNetworkOwner(nil)` keeps it server-owned; `SetNetworkOwner(player)` gives a player simulation ownership. Treat player-owned physics as untrusted and validate gameplay outcomes.

Server Authority: set `Workspace.AuthorityMode = Server` with its required settings. Core objects can remain server-owned while prediction keeps controls responsive, so the classic secure-but-laggy trade-off does not apply. `SetNetworkOwner()` is not a substitute.

**Rule:** choose the model first. Keep NPC and gameplay-critical objects authoritative; give client ownership to non-critical physics only when the resulting behavior is acceptable and tested.

### Common Gotchas
- Constraints do nothing on Anchored parts
- Both Attachment0 AND Attachment1 required (missing one = silent fail)
- Over-constraining = jitter. Tune mass with `CustomPhysicalProperties`
- Use Raycast for hitscan, `Touched` only for slow physics projectiles
- Always set a lifetime on physics projectiles
See `references/full.md` for recipes, API details, and checks.