A procedural Rube-Goldberg marble course — ramps, helical spirals, a narrowing funnel and a torque-driven see-saw. Each marble tracks an arc-length position along two CatmullRomCurve3 tube paths; its speed each frame is integrated from the local track slope (gravity along the tangent) minus a velocity-proportional friction term, so acceleration and braking emerge from geometry rather than scripted animation.