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Physics is the natural science that involves the study of matter and its motion through space and time."

-- Wikipedia

In Unreal Engine 4, physics are simulated using the PhysX 3.3 physics engine. All physics driven motion (physics bodies that are falling or have a force applied to them) and collisions (physics bodies interacting with each other) are managed by PhysX.Having physics in your game will help improve the immersion value of every scene, as it helps players believe that they are interacting with the scene and that the scene is responding back in some way or another.