A Dev’s Guide to Game Physics

Have you ever played a game and marveled at the way a tower crumbles realistically, how a car drifts perfectly around a corner, or how a character’s cape billows in the wind? As a budding game developer, you might see these moments and feel a mix of awe and intimidation. You might think you need an advanced degree in mathematics and physics to even attempt such effects, leaving you stuck and wondering how to bring that level of dynamic realism to your own projects.

The great news is that you don’t have to code these complex interactions from scratch. The solution and the secret weapon behind most modern games is a powerful tool known as a physics engine. This is the invisible workhorse that simulates the laws of physics within your game world, handling all the complex calculations for you. By understanding what a physics engine is and how it works, you can unlock a new level of interactivity and immersion, allowing you to focus on what matters most creating a fun and engaging experience for your players.

What a Physics Engine Actually Does

At its core, a physics engine is a specialized software component that simulates physical systems. In game development, this means it automatically calculates the effects of forces like gravity, friction, and momentum on the objects within your game. Instead of you having to manually write code to determine how fast an object should fall, how it should bounce off a wall, or how two colliding cars should react, the physics engine takes care of it based on the properties you define. It is the bridge between your creative vision and a believable, dynamic world that reacts to the player’s actions.

The two most fundamental tasks of any physics engine are collision detection and physics simulation, also known as the dynamics response. Collision detection is the process of figuring out when two or more objects in the game world are touching or overlapping. This could be a player character touching the floor, a bullet hitting an enemy, or a car bumping into a guardrail. Once a collision is detected, the dynamics simulation kicks in. This part of the engine calculates the appropriate reaction. It looks at properties like the objects’ mass, velocity, and bounciness to determine how they should move, rotate, or deform as a result of the impact, creating the realistic interactions we expect to see.

Key Physics Concepts Rigid and Soft Bodies

To effectively use a physics engine, you need to understand the main types of objects it can simulate. The vast majority of physical interactions in games involve rigid bodies, but understanding their counterpart, soft bodies, is key to creating truly next-level realism. These two concepts form the foundation of how you will build and define the interactive elements of your world.

Rigid Body Dynamics The Foundation of Game Physics

A rigid body is an object that does not change its shape or deform when it collides with other objects. Think of a bowling ball, a brick, a sword, or a wooden crate. In a game engine like Unity or Unreal Engine, when you want an object to be affected by gravity and to collide with things, you typically add a “Rigidbody” component to it. This tells the physics engine to start managing its movement and interactions. This is the bread and butter of game physics.

Once an object is designated as a rigid body, you can then fine-tune its physical behavior by adjusting its properties. You can change its mass to make it feel heavy or light, adjust its drag to control how much air resistance affects it, and set its friction to make it slide easily or stop quickly. Another key property is “restitution,” which controls its bounciness. A rubber ball would have a high restitution value, while a block of concrete would have a very low one. By playing with these simple parameters, you can create a huge variety of believable physical behaviors without writing a single line of complex math.

Soft Body Dynamics The Next Level of Realism

Soft body dynamics, on the other hand, simulate objects that can bend, deform, and squash when forces are applied to them. This is how developers create realistic cloth physics for flags and clothing, squishy characters made of jelly, or car bodies that dent and crumple on impact. These simulations are far more complex and computationally expensive than rigid body physics because the engine has to track the position of many interconnected points within a single object, rather than just the object as a whole.

Because of this increased performance cost, soft body physics are often used more sparingly and for key visual effects that greatly enhance player immersion. A character’s hair flowing as they run, a flag tearing in an explosion, or the satisfying wobble of a gelatinous cube enemy are all products of soft body simulation. While you may not use it for every object, knowing that this tool is available for specific, high-impact moments can help you add a layer of polish and life to your game that makes it feel truly dynamic and advanced.

Choosing Your Physics Engine Built In vs Standalone

For developers starting today, the choice of a physics engine is simpler than ever. The vast majority of popular game engines come with a powerful and highly optimized physics engine built right in. Unity has its own robust physics system, while Unreal Engine famously integrates a version of NVIDIA’s PhysX engine. These integrated solutions are tightly woven into the engine’s workflow, making it incredibly easy to add physical properties to objects and get predictable results. For nearly all indie and even AAA projects, the built-in physics engine is the perfect choice.

In some specific cases, a developer might opt for a standalone physics engine. Libraries like Havok (used in many AAA titles) or Box2D (a popular choice for 2D games) can be licensed and integrated into a custom-built game engine. This path offers more control but requires significant engineering effort. For anyone learning game development or working within an established engine like Unity, Unreal, or Godot, you can rest assured that the physics tools provided are more than capable of creating incredible, dynamic experiences. Your focus should be less on finding an engine and more on learning to master the powerful one you already have at your fingertips.