---
name: roblox-physics
description: "Use when building Roblox vehicles, ragdolls, projectiles, elevators, constraints, forces, or other physics-driven gameplay."
last_reviewed: 2026-07-13
sources:
  - https://raw.githubusercontent.com/Roblox/creator-docs/main/content/en-us/physics/mechanical-constraints.md
  - https://raw.githubusercontent.com/Roblox/creator-docs/main/content/en-us/physics/mover-constraints.md
  - https://create.roblox.com/docs/projects/server-authority
---

## 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
Replace Motor6Ds with `BallSocketConstraint`: create Attachments from motor.C0/C1, set `LimitsEnabled=true`, `UpperAngle=45`. Keep Root Motor6D for HRP. Set humanoid state to `Physics`. Re-enable motors to recover.

### 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 lifetime on physics projectiles (forgotten ones kill perf)
**Need more detail?** Load `references/full.md` for the complete reference with code examples, API tables, and edge cases.