Just when we thought we understood Physics!! - Page 1
Forum section: electronics / general

author: GlennSprigg
author_rank: Super Contributor
timestamp: August 27, 2020, 11:51:41 am
content: (If this was discussed before, then I'm sorry. I did 4 different searches).It's about the 3 (X, Y, Z) axis' of rotation of a spinning body, and depending on the 'shape' of the body, those 3 axis' have different momentsof inertia & centrifugal forces of the body's constituent parts. Now for some reason, the axis with the 'intermediate' level of forces, if it isspinning on that axis, the object will FLIP 180-deg at preset(?) intervals, repeatedly!!Evidently, people have labelled this the 'Tennis Racket Effect', where holding the handle and throwing/catching it in a circle always results inthe Racket turning over 180-deg. I personally am not convinced that this is exactly the same effect, that the latter part of the Video belowshows. It can't be any clearer, than the depiction of a Wing-Nut being spun off of a thread, in Space! It's quite mind-boggling to observethe Wing-Nut repeatedly 'flipping' over, and at regular intervals !!!An attempt is made at the Mathematics, but my old brain can not really grasp it now...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 27, 2020, 01:04:40 pm
content: It's simply* two simple harmonic oscillators, coupled. The energy swaps back and forth between the available modes, and the rate at which this happens is the oscillation frequency times the coupling coefficient (more or less).*For some degree of "simple". In this case, you'd have to know dynamics for it to be "simple", which... it's undergrad level, but it's not something trivial and obvious if you've not been to school. So, there's that.(Also, the motion isn't exactly SHM, it's continuous rotation; the dynamics are similar enough that I think this is explanatory, but I wouldn't bet much on this explanation until I've seen a more involved proof.)Related viewing:However, IIRC they cover the trajectory (which combinations of rotations are allowed), but NOT the rate of transition from one orientation to the next, which requires some more explanatory power (I think it might be hard if not impossible to avoid dynamics in that case, since after all, that's, well, the dynamics of the object's motion!).Tim

author: GlennSprigg
author_rank: Super Contributor
timestamp: August 27, 2020, 01:29:11 pm
content: ToT3sl4co1l. I will review the video link you supplied, again. To be honest, I only partially understood what you yourselfwrote. My own mental block was not just that there is obviously an initial un-ballance of forces, but that the objects inspace where *not* continuously tumbling as a result, but *cycled* between rotation & then brief stability again...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 27, 2020, 04:39:44 pm
content: It might very well look like chaotic "tumbling", if the exchange period is comparable to the rotation period, or something like that -- that's still a case of the flip-flopping motion, but it's just a lot harder to see!Tim

author: PlainName
author_rank: Super Contributor
timestamp: August 28, 2020, 11:50:48 pm
content: The chap in the first video seems a bit of a dork and I think I will give him a miss. But, usually, whenever I watch one of his videos I unexpectedly find myself at the end having watched it all. He explains well, and this particular video was no exception.OTOH, the second video may have proved something but I'm buggered if I know what. Lost me around the time of angular thingummy in three dimensions. Did they show the first guy was wrong? Maybe. Did they provide an 'intuitive solution' (even if it involved a little maths)? Not a chance. Well, not if it involved wading through that video first.

author: GlennSprigg
author_rank: Super Contributor
timestamp: August 30, 2020, 12:05:13 pm
content: Quote from: CJay on August 27, 2020, 05:28:01 pmThank you for your reply... (Yes, I've read about (thought I quoted?) those Theorum/Effect).I think I can grasp the 'sinusoidal' effects that you mention, one fast and one slow, but the 'Flip', (wingnut in space) does not 'appear' tovisually look like a sine wave pattern... as if when crossing a zero/peak point(s) while traversing/oscillating in it's movement??It looks as though after each rapid flip, there is quite a sustained period of stability on that axis. I will study it further!!

author: SilverSolder
author_rank: Super Contributor
timestamp: August 31, 2020, 12:59:47 pm
content: Maybe spinning in 3 dimensions turns the whole thing into the unsolvable, chaotic 3 body problem?https://en.wikipedia.org/wiki/Three-body_problem