Junior Member
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Oh boy, I get to do a science lesson!
Ok, "centripetal force is the correct term."
Not really. Let's start with the basics. Centripetal means "tends toward the center" and centrifugal means "flees from the center." Centripetal forces act to keep an object on a circular path. They have to counteract inertia, hence an acceleration towards the center of the circle.
The distinction comes from talking about what reference frames you're in. We're all used to inertial reference frames. If you're in an elevator that's moving and you treat the elevator as stationary, all the math still works. It just has to be adjusted. For example, normal gravitational acceleration near the Earth is 9.8m/s^2. If the elevator is moving accelerating downwards at 9.8m/s^2, things will appear weightless relative to the elevator. Newton's first law is sort of a crude explanation of reference frames.
The trouble arises when talking about non-inertial reference frames (such as a reference frame that is rotating). When working with these, the math doesn't quite work. To account for the happenings in these frames, you need to introduce the so-called fictitious forces. Examples are the Coriolis force and, indeed, the centrifugal force. It's a misnomer to just refer to the centrifugal force as a force. It depends on what reference frame you're in. However, in all inertial reference frames, it doesn't exist. So it's much simpler to call it a "centrifugal effect" or something.
To re-explain that, remember that an object will remain at a constant velocity when the net force on the object is zero. If you're in a rotating reference frame, you feel yourself being thrown outward. If you're in a car, for example, you're being thrown against the car door around a curve. The centripetal force is the normal force from the door, and maybe friction from the seat, etc. So, in this reference frame, it seems the net force is towards the center. This is where the fictitious force has to be introduced to make the math easier. In reality, though, the reference frame itself is rotating through two or more dimensions. And in all other inertial reference frames, the centrifugal force does not exist. Rather, these centrifugal effects are caused by the centripetal (center-seeking) force constantly accelerating you toward the center (and changing your direction at every moment).
Another interesting thing to note is that the fictitious centrifugal force pushes outward from the center of the circle. SUppose you're swinging a ball on a string. At any given moment, the string is providing centripetal force, and the ball feels a centrifugal effect. Intuitively, if you let the ball go, it would go exactly opposite the centripetal force. Not so, because the centrifugal force is not actually a real force. The ball would go tangential to the path it's on, due to inertia.
Again, it's all about the reference frames. If you're working in a non-inertial reference frame, the math works easier when you introduce the fictitious forces. Otherwise, they are due to Newton's laws and kinematics. There is no such thing as a real centrifugal force. But it's not exactly wrong to call it such, because it does exist in a mathematical form under certain conditions. And MIT scientist would completely understand the distinction, but it's just convention.
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