The brain becomes useless if the heart pauses > 5 sec.
The heart becomes useless if venous return stops.
No venous return, no cardiac output.
Venous return by motor activity including breathing.
Motor activity is under gravitational influence.
An assumption of frictionless slide is not going well with a cycloid.
A cycloid has a contact point on the ground & friction makes the bead/ball rotate.
G pulling w/ friction rotates bead/ball.
Quicker initial rotation (accel) by front void under G makes brachistochrone curve.