Interactivity in Unreal Engine relies heavily on collision and physics systems. Day 20 introduces you to collision channels, trace responses, and how objects interact physically in the engine.

You’ll start by learning about collision presets: Block, Overlap, and Ignore—and how to assign them to different components. Using trace channels, you’ll enable features like line-of-sight detection, bullet traces, or interactable object highlights.

Next, you’ll explore physics simulation—applying gravity, bounce, force, and friction. You’ll simulate a realistic environment where balls roll, crates fall, and glass shatters. Using the Physics Constraint component, you can also build chain-like behavior or hinges for doors.

Blueprints will help you apply force or torque based on user input—like pushing objects or using physics handles to drag them around (à la Half-Life: Alyx or Portal).

You’ll also build a trigger box system—enter the zone, and it activates a trap or opens a gate. This blends collision logic with gameplay mechanics.

By the end of the day, you’ll understand how to use physics to add realism and how collisions can drive complex game interactions.