The document discusses the new features of PhysX 3.3 in Unity 5.0, including a rewritten SDK with improved multithreading and new subsystems for vehicles and cloth. It provides overviews of the Rigidbody component, Cloth component, and new WheelCollider. Performance is improved through multithreading and faster algorithms. While PhysX 3.3 is not fully compatible with previous versions, Unity 5.0 physics is now twice as fast and supports more modern platforms and CPUs.