# Reference frame and centrifugal force

Imagine you are on a theme park ride in which you sit in a car and are spun around in a circle, basically like a giant centrifuge.

An observer from the outside would say that there is no centrifugal force acting on the person in the car, only centripetal. However, for the person in the car, there is the force pulling them inwards (centripetal), and its reaction force pushing outwards against the side of the car (centrifugal). However, from this point of observation, the person in the car is stationary and everything else is moving around him.

Does this not mean that there is no circular motion in this frame of reference, and therefore the reaction force is not centrifugal, as there is no circle centre? Basically, I am confused as to why a fictitious centrifugal force will show up in a frame of reference where circular motion is not occurring.

• possible duplicate of Centripetal force in frame of reference of body moving In a circle Apr 22, 2014 at 15:27
• The answer to that question refers to the forces as centripetal/centrifugal. What I am asking is why are the forces called this? 'Centrifugal' force implies a force acting away from the circle centre, yet in this frame of reference there is no circular motion and no circle centre, but it (the reaction force) is still called centrifugal force. Why is this so? Apr 22, 2014 at 15:50
• Your comment here appears to be entirely different from the question itself, then. Apr 22, 2014 at 15:52
• The reason circular motion is not occurring in that frame of reference is because the fictitious centrifugal force was introduced, otherwise there would just be centripetal force and there would be circular motion. If it still doesn't make sense, that's good. This is meant to show that classical newtonian physics does not always apply to a frame undergoing constant acceleration
– Jim
Apr 22, 2014 at 23:50