
Originally Posted by
CEC
Newton's laws contain the principle of inertia; that a moving body, if unaffected by any forces, will travel in a straight line. A coaster train is affected by forces along its run (the force of gravity, as well as the supporting force of the track), but if it is travelling along a straight-away, none of the forces will be directed towards either side. The riders, too, will not experience any forces to either side. On the other hand, if the train hits a curve, it will tend to want to go forward. The track has to exert a sideways force on the train to divert it from its path. The train, in turn, exerts a force on the riders. As they continue to try to go straight, they get pinned to the side of the car. Though they feel themselves being forced toward the outside of the curve (an effect commonly referred to as centrifugal force), the force that is exerted on them is actually towards the inside (centripetal force), because that is the direction in which they are turning. As with forces directed vertically, lateral forces can be measured in terms of Gs. A 1-G lateral force would be equivalent to your lying on your side.
Several factors affect the strength of lateral G forces: the speed of the train, the tightness of the curve, and the amount of banking. The faster the train goes through the curve, the greater the force required to keep it on the track. Similarly, the tighter the curve, the more force is exerted on the train. For example, the train going through the helix section of the Kennywood Thunderbolt is moving quite fast, because it has just come off a substantial drop. This explains its legendary lateral Gs. On some coasters, the curve may also contain a drop. In this case, the train speeds up through the curve, and the G forces get stronger. The Riverview Bobs contained two dropping turns of this sort with little banking. Pictures show the riders pinned to the outside of the car, as one would expect.