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Here’s a random memory triggered by an unrelated Facebook post I read.

When I was a physics major, one of my professors, referencing a carnival ride, actually said, “Centrifugal force doesn’t exist. What you’re experiencing is centripetal force pushing you in.”

I responded, “But if centripetal force exists, doesn’t Newton’s Third Law of Motion demand that centrifugal force also exist? Wouldn’t that be the force your body exerts back on the wall?”

Boy, was he pissed. Of course he knew that the “reactive centrifugal force” existed. This is the force that you exert on the wall in reaction to the wall pushing you towards the center. It’s a very real force. However, even back then, I was killing people for linguistic imprecision. I couldn’t help it. It was a legitimate question brought on by a quirk in how physicists label these topics.

“Centrifugal force” is used differently from “reactive centrifugal force,” which is stupid. All forces have a reactive counterforce, so why qualify it as “reactive”? Unfortunately, that’s the linguistic convention, but when you say “centrifugal force doesn’t exist,” it misleads people who otherwise have a grasp on what you’re teaching. Physics professors should make it clear that there is an outward force, but we experience a misperception that this outward force is acting on us. In fact, the outward force is acting on the wall (or whatever is forcing you to take a curved path). Without “reactive” modifying it, “centrifugal force” refers to the misperception rather than the very real force.

If you want more details on the physics, here’s a relatively short lecture on this topic (about 12-1/2 minutes), though it doesn’t discuss the issue I’m raising here. In fact, it makes the same mistake. I originally provided a paragraph explaining some concepts the lecture takes for granted, but that paragraph would probably have made things worse. 🙂

You may have expected this to be about science, or language, but it was really about me being a pain in the ass.

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