Centripetal Forces

On a looping coaster, the general rules of centripetal force are in operation because the train is making a turn at every point during the loop. The force that makes the train turn through the loop is centripetal force. As the train starts the loop, gravity and momentum are pulling the train out of the loop, so the structure of the track provides the "seat force" that moves the train through the loop-- the centripetal force. On its upward climb, the train reaches a point where gravity is no longer pulling it out the loop and thereafter it is acting as part of the centripetal force pulling the train toward the center of the circle