I don't really understand how the centripetal force arises from driving on a banked curve. There are three forces acting on a car in circular motion on a banked curve: normal force, gravity, and applied force. Let's assume that there is no friction, and that somehow the car is already at a constant speed. In this case, there are only two forces; gravity and the normal force. Essentially, what allows the normal force to keep the car moving on the ramp? Assuming no friction, gravity will always pull the car down the ramp if its velocity is zero. However, when it's greater than some threshold, the car maintains its motion on the ramp. How does this work? Why does changing the velocity change your ability to stay on the ramp in constant motion? Why doesn't gravity just pull down in every case?