Could centrifugal force be appropriately described as motion (inertia)--rather than an (imaginary) force? Could such a change of perspective eliminate much of the common confusion?
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$\begingroup$ This is correct and is actually the consensus in Newtonian Mechanics: Centrifugal Force is the the name given to the spontaneous acceleration experimented by bodies as measured within a specific type of non-inertial reference frames. Those frames being rotating when observed from some inertial reference frame. $\endgroup$– rmhleoJan 26, 2016 at 15:04
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$\begingroup$ There is nothing "imaginary" about centripetal forces. Ultracentrifuges with up to 2000000g of acceleration are commercially available and the mechanical construction of these machines requires enormous care for the real forces that are being generated by their very fast spinning innards. The confusion you mention arises about fictitious force. i.e. the seemingly weird movement of inertially moving bodies when seen from non-inertial coordinate systems. Motion of bodies in a circle requires a real force, not a fictitious one. $\endgroup$– CuriousOneJan 26, 2016 at 16:20
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2 Answers
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It is indeed like this. Centrifugal force is the virtual force experienced in a non inertial frame that is rotating, the reason why we always hear about it and rarely about its "real" counterpart, centripetal force, is because we tend to set our mind in the simplest referential frame to interpret. So if we are in a car or in a bus and it turns, ore even if we are just looking at it from the outside, we will instinctively put ourselves in the bus frame, where thing will accelerate toward the direction opposed the center of the curve so if we want to apply Newton laws in our referential frame we have to suppose a force directed that way, centrifugal force indeed. If we analyze the same thing from an inertial frame than we see that things are just going straight and the bus is accelerating in the other direction.
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This is a big source of confusion, and from a pedagogical standpoint, I'm a fan of trying to eliminate the terms "centripetal force" and "centrifugal force" wherever possible. In the classroom, I try to emphasize that "centripetal" and "centrifugal" are just directions (towards and away from the center of a circle respectively) just like "up," "down," "East," and "Into The Page."
We don't talk about an "up force" or an "east force," -- we say "the ball feels a net force in the upward direction." Similarly, I try to get people to think about what's behind the centripetal or centrifugal forces. There's always a reason for the force (gravity, rocket engines, etc.) and if not, it becomes clear that the force doesn't really exist.
Here's an example of what I'd want a student to be able to say: As a car goes around a curve, there is a friction force by the car seat on the passenger's back, and rear end pointed in the centripetal direction. This force keeps the passenger accelerating into the curve. Meanwhile, the passenger feels as though something is pushing her in the centrifugal direction. On closer examination though, she realizes that there is no force pushing her outward, so she realizes that this is just a consequence of Newton's First Law, which says that her body would prefer to continue in a straight line.
If I ruled the world, I would get rid of the words centrifugal and centripetal and fictitious force because they are clumsy, and easily described by more common words/concepts. Of course I don't, so I still talk about them!
