Uncle Hyena (unclehyena) wrote,
Uncle Hyena

Centrifugal Fiction

I have just finished Andy Weir's "The Martian" (GREAT movie, even better book), and was disapponted to learn that Mr. Weir suffers from the "Fictitious Force Fallacy". One can't have everything.

At some point during the study of physics, the student inevitably encounters the idea that centrifugal force is a "fictitious" force. Some students come away from this lesson with the impression that they must never again speak of centrifugal force, but instead refer only to centripetal force. This is always awkward and usually wrong.

The problem begins with the fact that, when a physicist refers to centrifugal force as a "fictitious" force, he is using the word "fictitious" in a technical and non-intuitive fashion. The label derives from the fact that, at some point in the wild days before Isaac Newton, centrifugal force was regarded as a thing unto itself, and not just a known property of matter reacting to special circumstances. In that sense, and that sense only, centrifugal force is a fiction. This will not prevent it from rolling your car if you take a turn too fast.

Consider the following:

One: John was smashed against the wall by centripetal force. This is a nice, straightforward sentence (It's passive voice, but live with it. Really.) It is also BAD physics, but exactly the sort of thing that people who suffer from the Fictitious Force Fallacy tend to write.

Two: John was smashed against the wall by centrifugal force. This is grammatically identical to the first sentence, and better physics. It isn't as precise as it could be; see below.

Three: John was smashed against the wall by the centrifugal effect of the station's motion. This is bad writing, but a bit more accurate than #2, above.

Four: John was smashed against the wall by his inertia reacting against the centripetal force supplied by the station's wall. This is good physics and awful writing.

Takeway: Centrifugal force is the inverse of centripetal force, and is far easier for the human brain to understand than the pedantic details.

Uncle Hyena
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