Which of the following statements is physics-based and describes the forces acting on a vehicle negotiating a curved path?

1. The centripetal force acts radially outward from the center of curvature.
2. The centrifugal force is a real action-reaction pair force experienced by an external observer.
3. The centripetal force acts radially inward toward the center of curvature to keep the vehicle in a circular path.
4. The vehicle does not require any frictional force if it is traveling on an unbanked curve.