this post was submitted on 05 Nov 2025
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Explain Like I'm Five

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How is centrifugal force a ficticious force? (lemmy.world)
submitted 1 month ago by ComicalMayhem@lemmy.world to c/explainlikeimfive@lemmy.world
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I understand that in order for an object to maintain circular motion, its velocity vector must be travelling perpendicular to its position vector and constantly changing inwards, hence an acceleration towards the center of the circle. I know that the acceleration towards the center is typically caused by other forces, like tension on a string, and that these are called centripetal forces I believe? However, objects in circular motion tend to want to be away from the center instead of towards. A bucket of water tied to a string and twirled around in a circle will result in the water staying in the bucket: if the water is exhibiting circular motion, would it not thusly be accelerating inward, and thus escaping the bucket? I've heard that it's a difference of frame of reference, but even looking from out to in, I can't see how the water would be accelerating inward and yet remain in the bucket without support. Would there not be some force pushing the water into the bucket? And yet, centrifugal force is considered a fictitious force. I don't understand. I know I understand some level of physics but please explain it like I'm 5 because I can't seem to actually understand this.

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[–] sp3ctr4l@lemmy.dbzer0.com 0 points 1 month ago* (last edited 1 month ago)

'Fictious force' is a poorly phrased term, maybe you could say its a misnomer.

Its more like an emergent, or secondary force, as opposed to a fundamental or primary force.

It isn't 'fictitious', as in, wholly not real, its more like 'contingent'... these rules well describe many realistic and common scenarios and their behavior, but they're not perfectly universal, they require common, but not strictly universally present conditions.

Like uh, lift, drag, acting on an aircraft wing... those are also not literally fundamental, base level forces of the entire universe... but they are functionally real forces, in a certain context, in certain conditions.

Now put a bunch of small wings on a stick, spin it real fast, we tend to call that a propeller or a helicopter... maybe a jet intake turbofan... and you will find that the 'fictitious force' of the centrifugal effect, well, it becomes a pretty reasonable and also relevant rule to understand, if you don't want your thing that's spinning really fast to literally rip itself apart.

Other examples of this might be the 'Van der Waals force'... again, a reasonably real thing, in certain contexts... but not wholly fundamentally real, in literally all contexts.

Casimir force / pressure / effect might be another one.

Turns out that the ambient background of quantum foam potentialities can actually create measurable physical pressure differentials at very, very small scales.

... that one kinda actually is inherent to all reality.

But its basically just never relevant to anything beyond nano engineering.

???