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Desc:Funny how simply rigid bodies spinning can still be hard to understand sometimes
Category:Science & Technology
Tags:physics
Submitted:Mr. Purple Cat Esq.
Date:04/17/17
Views:658
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Comment count is 8
Bort
I think the same effect can be seen with books too. Take a normal rectangle-shaped book. There are three basic axes of rotation: the one that goes top to bottom, the one that goes left to right, and the one that goes front to back. If you toss the book in the air and spin it along the top-to-bottom or front-to-back axes, it wobbles in the air a tiny bit; but if you try to spin it along the left-to-right axis, it's going to spin all unpredictably.

It's been 30 years since I did the math on this, but the basic deal is, on the largest and smallest moments of inertia*, any small motion on the other axes results in a sine-wave wobble; while on the middle moment of inertia*, those small motions throw the whole system increasingly out of whack.


*: Moment of inertia: think of it like the cross-section as the book rotates. Like for the left-to-right axis, look at the spine of the book. You get the smallest cross section with the top-to-bottom axis -- look down at the top surface of the book -- while you get the biggest cross section with the front-to-back axis, looking at the front of the book like a normal person.
15th
I dunno, man, I typed "spinning book" into Chegg and nothing came up.

Mr. Purple Cat Esq.
You may find this interesting

https://mathoverflow.net/questions/81960/the-dzhanibekov-effec t-an-exercise-in-mechanics-or-fiction-explain-mathemat

Oscar Wildcat
It's not a bad example of how seemingly unfathomable quantum mechanical effects ( like a particle with two discrete spin states ) can have a real classical analog. I take heart from the fact that younger researchers are pursuing this idea and coming to some interesting physical systems that display most of the previously thought incomprehensible quantum effects. Google around on the term "quantum realism" for more information.

Old_Zircon
I read a book about quantum realism a few years ago, but the guy who wrote it taught at Brigham Young University so I didn't really know how seriously to take it.

Oscar Wildcat
Depends what the book said, but about the general idea, quite serious. The system most studied is a drop being bounced above a liquid surface. The resulting wave/particle interacts with other drops and the environment just as individual quanta do. It's a physical analog to the De Broglie pilot wave.

Hazelnut
Iunno, I googled it a bit and it seems to be this one Brian Whitworth guy who sounds pretty Time Cube to me:

"the big bang should have made equal amounts of matter and anti-matter, so where are the anti-stars, anti-planets and anti-meteors? The current answer is that somehow matter overcame anti-matter, i.e. yet another “miracle”. Now consider a simpler option. All processing sets a sequence of values that by definition can be reversed, so any matter made by processing must have an anti-matter version. Why then are there no anti-matter stars? If our universe began from one photon, it had to choose to move up or down with respect to space. In our case it went first up and the other photons followed suit so light collided into an electron bump. If it had gone first-down light would have collided into anti-electron dimple. This initial choice made our universe matter and from then on anti-matter was a path not taken. So the anti-matter physics is trying to explain never was and no physical reason for this will ever be found."

I mean, first of all they've made antimatter in the lab, and second he's not capitalizing Big Bang. So I think probably crazy person.

Oscar Wildcat
Yes, well that is crazy nonsense, of which there is no end of.

Here is what I am talking about. Pilot waves for dummies.

https://www.youtube.com/watch?v=WIyTZDHuarQ

For the more erudite.

https://youtu.be/nmC0ygr08tE

http://math.mit.edu/~bush/wordpress/wp-content/uploads/2013/10 /Gallery-Harris-2013.pdf

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