Usually a roller coaster represents constrained fall. The track holds back the train's path, so it won't use the same trajectory as it would if the track wasn't there. Some of the simplest examples of constrained fall are represented by Galileo's inclined planes. The constrained fall is different from the parabolic fall in that the inclined plane provides part support for something falling down, which prevents it from falling as fast as it normally would. The main rule of falling down an inclined plane is that the falling object will accelerate faster the steeper the plane is. When the plane is vertical all of the way the object will be in free fall, which is the fastest gravitational acceleration.
