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The Dzhanibekov Effect: If You Are an Old-Timey Scientific American, You Will Like this Video
For years, the subtype of Homo americanus called “scientific American” was a market demographic big enough, rich enough, and loose enough with a buck to support the eponymous magazine.
(Note: Sadly, the magazine died about two decades ago, and was absorbed by the propaganda forces of the proggy church, which deceitfully maintained the name, in accordance with their doctrine.)
If you are one of those fanatically dedicated amateurs, I guarantee you will love this video, or your money back.
The unwritten Code of Conduct might require me to give you, the reader, some content, not just a link to the content.
Here, then. It involves a mysterious physical phenomenon: some spinning objects sometimes suddenly flip over and start spinning in the opposite direction!
I could also give you this content: the USSR came up with a theory about it and tried to keep it secret for years!
But that’s all I can say. If you are one of US, and not one of THEM, you will watch the video, and then share your thoughts with me, because I am one of you.
Published in General
Related to this topic is the tippe top, which also behaves in an unexpected manner.
Two prominent physicists of the 20th century (Wolfgang Pauli and Niels Bohr) at a conference trying to figure out how it works:
Doc,
First, thanks for the historical correction. You should find the Euler paper and then write to Veritasium with the correct info.
But re the above comment, do you think you could create an intuitive derivation of what determines that rate? (It would have to be an ordinal explanation, I guess? since a cardinal explanation would be mathematical by definition.)
Just now, I began the thought experiment. I am imagining one of the lighter masses, in its own frame of reference. It is stationary at first. Then it experiences an upward impulse. That would give it an upward velocity, and also an increasing (unexplained) centrifugal force.
Okay, well, that’s as far as I got! You can take it from here.
That depends on how fast Guam is spinning, doesn’t it?
Earth is already rotating about its axis with the greatest moment of inertia, and hence the lowest kinetic energy. No matter how much kinetic energy Earth sheds, it will continue to rotate about that axis.
That’s it! Good job.
I think this is the first half of an intuitive explanation:
If the object’s rotation is purely and precisely balanced about any axis, and the distribution of mass (the “moment of inertia”) is also perfectly balanced about that axis, then the rotation will continue unchanged forever. The least push away from that equilibrium will produce some force about the other axes. (There’s more than one line thru this object that has a balanced distribution of mass around it.)
That was my “short answer” comment. These things happen because the model requires perfection which neither man nor nature (and man is part of nature) can produce.
But haven’t the magnetic poles flipped occasionally?
Yes. In fact, the video introduces the question, could the Effect be somehow related to the poles flipping in the past? It only goes on to say that there is no possibility of this phenomenon flipping the spin axis. It never really addresses your question directly.
Well the liquid core could be less stable on that axis.
At first I thought the size of the perturbation would be critical but changed my mind after considering that the initial growth in the flipping motion is exponential, so the size of the initial nudge doesn’t matter much. Recall that there has to be a slight (inevitable) deviation from main rotation axis.
The only natural timescale in this problem is the rotation period of the object; the faster it spins, the faster it will flip over. One could test this theory by starting the thing off at different spin rates: easier to test in microgravity than here on Earth. A frame-by-frame analysis of the video embedded in the OP seems to support this as the spinning thingie slows down a little from air resistance. Too bad it didn’t go a bit longer.
Undoubtedly, everyone else has already lost interest in this trivial point.
I guess I don’t find it particularly fascinating because, as my comment early on, it’s just because neither nature or people (part of nature) can make anything geometrically perfect, or cause it to spin perfectly. I suppose it might complicate matters some for certain engineering fields, but I expect they’ve been aware of that for quite a while. (Although such things do still crop up on occasion, such as the infamous library that was constructed without taking into account the weight of the books it was supposed to contain.)
That’s more complicated on two counts – there’s fluid involved, not just a solid body, plus magentism. I didn’t think the core is supposed to physically flip during a pole reversal but … maybe it has to.
How perfect would it have to be, to avoid the middle axis instability? It’d have to be perfect at least all the way to the classical limit. It’s not that nature can’t make anything that regular, it’s just that’s not how nature works.
Boy, the math on this is a horror. I wonder if Lagrangian mechanics is actually not the way to do this.
The point is, it would have to be PERFECT. Otherwise, eventually, it’s going to go off-kilter. Although if you get something really close, it might theoretically take years, centuries, even eons for it to happen. And most people would be satisfied with that.
My point is, there’s no such thing in any field anywhere, as that notion of perfect. It’s not even an abstraction, even if you capitalize it.
That was part of my point too, it’s always going to happen in the real world, so being somehow surprised by that, or spending more than a second on a theory that’s never going to play out, seems useless.
Your logic is easier to work out and fix than the intermediate axis theorem, so I’ll stick with it a little longer. Let me rephrase: you are uninterested in the phenomenon because it conforms to nature. Is that correct?
Well, uninterested may not be quite right. Unsurprised may be more accurate. I don’t get why people think this is so amazing when it’s really just because nothing people make, and nothing in nature either, has the perfection for that to NOT happen, eventually. And anyone who has ever ridden a bicycle should know better too. It’s like how you turn too sharply, and then try to turn back, and then wobble wobble, back and forth, and then BAM! The same thing can happen with cars and other vehicles too, of course, but it seems less common.
But that’s not so. Almost nothing behaves like this, at least on scales that humans in a gravity well get to observe. Many many things are not perfect. Almost nothing demonstrates the intermediate axis phenomenon.
But the intermediate axis phenomenon will exist for any natural or human-made object that is capable of it, because nothing nature or humans (part of nature) make will be perfect so that it WOULDN’T happen.
Seriously, this “amazement” strikes me as like being “amazed” that something falls when you let go of it.
“If I let go of a hammer on a planet that has a positive gravity, I need not see it fall to know that it has in fact fallen.” – Spock
Well, I know classical physics ok, and I’m comfortable with physically manipulating things, and I find it amazing. But then I’m surprised when I hold a spinning bicycle wheel and try to turn either me or it. The cross product isn’t intuitive unless one can see what transmits the force.
Wow.
I don’t know why the rotation flips, I just know under what conditions it flips. I’ve never had an intuitive sense of computational physics — nor an intuitive sense of anything mathematical, in fact, other than the basic concepts of and differences between simple and complex dynamic systems.
But the thought of a stable rotation around an extreme axis reminds me of a super-cooled fluid, poised to change state at the slightest disruption.
I think the main point is, once the rotation becomes unstable, it HAS TO flip.
Barfly and kedavis,
I am kind of in the middle of the road on this.
I would be amazed if it did NOT fall.
I would be amazed if that were NOT true.
Unlike kedavis, but like most people, I don’t find it intuitively obvious that the behaviors 3.1 through 1.4 must result from #2, with the given axis being the intermediate axis.
kedavis, I have been wondering if it is also intuitively obvious to you that the wingnut would NOT act this way if you chose any other axis.
It was while having gyroscopic torque explained to me as a young man that I first realized that, as much as I enjoy the subject, I don’t get a lot of physics. I still find forces exerted in unexpected directions unsettling.
We all take gravity and magnetism for granted: they’re fields with which we’re familiar, only really amazing when you pause to think about them. And the thought that we are likely actually composed of fields, that there is very little that’s physically “real” in the world around us — i.e., that it’s mostly empty space, that the particles that make it up have a chimerical quality — is itself unsettling. To me, anyway.
Me too. When I see an everyday phenomenon like that of a gyroscope that I do not have an intuitive understanding of, it is like going through life with a splinter in my heel. I have to get rid of it, and the urgency does not go away for days and weeks and months. It will wake me up in the middle of the night.
I have to understand it. “Understand it” means to break it down into simple patterns that are already intuitive to me, like gravity. I have to see the behavior of the spinning racquet as merely another specific example of a certain kind of cause having a single possible effect.
I hated high school physics each time new topic came up. The teacher would think he was explaining it by writing symbols on the board, and then applying symbolic (algebraic) transformations to it like “moving X to the right side of the equation”. Big time splinter.
I got an F in physics once on my report card.
Even in the Veritasium video it happens: “it changes axis of rotation because both energy and angular momentum have to be conserved”. That favorite “explanation” of the schoolmar’ms of physics is more like a splinter in my eyeball!
I had to work through mechanistically, “what does it mean for the axis to change because the kinetic energy decreased?”
The reason I excel at Austrian economics is that all the mystical nonsense of modern “mathematical” economics thinking, and claiming that calculated aggregates of real facts, like “inflation” and “unemployment”, can be causes or effects, is discarded.
Your mind starts at the very beginning, with nothing but intuitively obvious facts, and it proceeds logically, common-sensically from there, until finally all economic phenomena are understood by a single unified theory. Not one theory for individual prices and another for “general price level”.
Don’t take all that too seriously. QFT and GR aren’t reality, they’re just models.
That could be true. But I’m not confident that that is true.