Centripetal force in loops
Loops are engineered so the track pushes you into the seat — not so you “hold on by gravity.”
In a vertical loop, the train is always changing direction. Your body wants to travel straight; the seat and restraint provide centripetal force toward the center of the curve.
Well-shaped loops enter with enough speed that positive G keeps you seated through the top — early rough loops were tear-shaped partly because designers were still learning optimal radii and transitions.
Heartline elements rotate the train around your chest instead of the track center — different force paths, often smoother head feel.
If a loop feels rough, it may be transition geometry (how quickly curvature changes), not just “too much speed.”