Why is Centrifugal force “not real”? I remember my physics teacher in high school pushing that idea and understanding why back then, but I do not remember now. I also forgot so much about physics in general that a simple would be much appreciated!
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Centrifugal force absolutely *is* real. It’s just fictitious, because it’s not real *in an inertial reference frame*.
Let me ELI5: let’s say you, a 5-year-old, hold on to a rope, and I swing that rope around and spin you. (I think I can still do that to my 5-year-old, but she’s getting a bit too big now. Anyway.) What will that feel like *to you*? You’ll want to hold on tight, because if you let go, you’ll *shoot* off. That’s a force pushing you *away* from the center — centrifugal. What will that feel like to *me*? Well, I’m spinning you, so I’m actually pulling you towards me at the center — I’m exerting a centripetal force. When you’re spinning, what you actually want to do is travel in a straight line, so I have to pull you into me so that you turn around the circle instead.
For me, I’m standing still in a frame that’s moving at constant velocity — in this case, velocity 0 relative to the ground — and I’m *exerting*, with my arms, a centripetal force to pull you in and keep you from traveling in a straight line. You are moving around in a circle, so what you feel is a force pushing you *out* of the circle, and if you let go, you’ll go flying off out of the circle (which to me looks like you traveling in a straight line).
If we think only about frames of reference moving at constant velocity — what we call inertial frames — then there is no centrifugal force; it’s fictitious. But when we talk about frames that are *not* moving at constant velocity, like frames going around in circles or otherwise accelerating, you *do* feel a centrifugal force. You do actually feel it; it’s real to you. But what you’re really feeling is the acceleration of the frame itself. We call it a fictitious force because it doesn’t exist in an inertial frame. Other fictitious forces are the Coriolis force (which pushes you in fairly weird ways), the azimuthal force (has to do with acceleration of rotation, very complicated), and the good ol’ linear acceleration force, which is the force that pushes you forward into your seatbelt when your mommy brakes the car really hard. These are all forces that you feel not because something is applying that force on you but because of how you’re moving.
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