Forces That Make a Roller Coaster Loop

A roller coaster navigates a vertical loop through the interplay of two forces:

1. Gravity (Weight): Acts downward through the train's center of mass.
2. Centripetal Force: Directed toward the center of the curved track, provided by the normal force from the rails.

At the loop's top, gravity and centripetal force both point downward; their sum provides the necessary centripetal acceleration. If speed is sufficient, the train stays on track. As it descends, gravity exceeds the required centripetal force, accelerating the train. At the bottom, the normal force (centripetal) exceeds gravity, decelerating the train. This cycle repeats through each inversion.