Sliding Friction

When the track is curved upward, the load wheels will roll smoothly, but the guide wheels will be sliding somewhat, in addition to rolling. This is caused by the curvature in the track. Similarly, when the coaster is navigating a flat turn, the guide wheels will roll smoothly, but the load wheels may slide. This sliding friction can be modeled as Coulomb friction, and varies linearly with the force exerted on the sliding wheel normal to the direction of the sliding. This force should only be considered for the wheels which are sliding.