Game Physics & Collision Systems is the layer of a game engine that turns raw positions and velocities into believable motion, impacts, and stacking, sitting beneath animation and gameplay code in engines from Unity and Unreal to Godot and custom C++ frameworks. It matters because a physically convincing world is what lets a player trust that a thrown grenade rolls the way it should or that a stack of crates topples believably instead of floating or jittering; get it wrong and the illusion breaks immediately. The core insight to keep in mind while scanning these tables is that the pipeline is a strict sequence: broad phase narrows millions of possible pairs down to a handful of candidates, narrow phase decides exactly how those pairs touch, and only then does a constraint solver turn that contact information into forces bodies actually feel — mixing these stages up, or skipping continuous detection for fast objects, is where nearly every physics bug in shipped games originates. This sheet assumes you already know your engine's vector and transform math; it focuses purely on rigid-body dynamics, the two-phase collision pipeline, and the constraints and joints that hold a simulated world together.
What This Cheat Sheet Covers
This topic spans 15 focused tables and 109 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
A jump-to index of every table row in this cheat sheet.
An interactive map of every table and concept in this topic.
Table 1: Foundational Rigid Body Concepts
Every physics engine simulates the same handful of building blocks underneath very different APIs; knowing these terms makes every other table in this sheet easier to read.
| Concept | Example | Description |
|---|---|---|
position, orientation, mass, shape | A solid that cannot deform; the standard abstraction game engines simulate for stones, crates, and vehicles. | |
F = ma | • Inertia: no force, no change in velocity • Force = mass × acceleration • Every action has an equal, opposite reaction | |
$a = F/m$ | Net force divided by mass gives acceleration; heavier bodies accelerate less under the same applied force. | |
$\tau = \mathbf{r} \times \mathbf{f}$ | Rotational analogue of force: the cross product of the offset from the center of mass and the applied force. | |
Rigidbody.isKinematic = true | • Dynamic: driven by forces and collisions • Kinematic: moved by code, ignores forces but still pushes dynamic bodies • Static: never moves |