What Game Engine Physics Can and Can’t Do for Indie Devs

Unity, Unreal, Godot—they all ship with physics engines. Rigid bodies, collisions, joints, and sometimes cloth and soft bodies. For indie devs, that’s a lot of power out of the box. But physics engines have limits. Knowing what they can and can’t do saves you from fighting the wrong battles—and from building systems the engine wasn’t designed for.

What physics engines handle well

Rigid body dynamics are the core strength. Objects with mass, velocity, and collisions—blocks falling, balls bouncing, characters ragdolling. The engine handles integration, collision detection, and response. You configure mass, friction, restitution (bounciness), and constraints. For platformers, puzzle games, vehicle sims, and anything with physical objects bumping into each other, the built-in physics is usually sufficient.

Constraints—joints, hinges, ropes—let you build complex structures: ragdolls, vehicles, destructible objects. Revolute joints, prismatic joints, fixed joints, and distance constraints give you a lot of flexibility. Many indie games ship without ever touching custom physics.

Where physics engines struggle

Determinism is hard. Different platforms, different frame rates, and floating-point rounding can produce different results on different machines. For single-player, that’s rarely a problem. For multiplayer, it’s a nightmare. Networked physics typically requires either authoritative server simulation, deterministic lockstep, or carefully designed prediction and reconciliation. The engine won’t solve that for you.

Performance at scale is another limit. Thousands of rigid bodies with complex collisions can tank frame rate. Broad-phase optimization helps, but there’s a ceiling. Games that need massive destruction or huge numbers of simulated objects often use simplified or custom systems—LOD for physics, reduced precision, or spatial partitioning.

Soft bodies, cloth, and fluids are supported in some engines but are computationally expensive. Indie projects often avoid them or use pre-baked simulations. Real-time cloth on every character is a luxury; pre-animated or simplified cloth is the norm for small teams.

What physics engines can’t do

They won’t design your game feel for you. Physics parameters—mass, friction, restitution—affect how movement feels, but tuning is manual. A platformer’s jump feel comes from tweaking gravity, jump force, and coyote time—not from “realistic” physics. The engine provides the simulation; you provide the design.

They won’t handle gameplay logic. Collision callbacks tell you something hit something else; they don’t tell you what that means for your game. Damage, scoring, state changes—that’s your code. The physics engine is a black box for simulation; you wire it to your game logic.

They won’t guarantee stability. Complex constraint systems can explode—objects flying off, jittering, or tunneling through geometry. Stabilization techniques exist, but weird edge cases happen. Testing and iteration are essential. Sometimes the right move is to simplify: fewer joints, simpler geometry, or a different approach entirely.

When to build custom

Most indies should stick with the built-in physics. The ROI on custom physics is low unless you have a specific need: deterministic multiplayer, extreme scale, or a mechanic the engine doesn’t support. If the built-in system gets you 80% of the way, ship with it and iterate. Custom physics is a rabbit hole.

When you do need custom—arcade racing with fake physics, a specific destruction system, or 2D physics with different rules—consider hybrid approaches. Use the engine for some things and custom code for others. Offload expensive simulations to a lower frequency or a separate thread. The goal isn’t purity; it’s shipping a game that feels right.

The bottom line

Game engine physics are powerful and underused by many indies. They’re also not magic. Understand their strengths—rigid bodies, constraints, collision—and their limits—determinism, scale, feel. Use what the engine gives you; customize only when you have a clear reason. The best physics are the ones players don’t notice—they just feel right.