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Author Topic: Mysterious optical effect of spiral on stem  (Read 1465 times)

ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #15 on: May 08, 2024, 11:16:49 PM »

Very good work!

With the wobble and the spin in the same direction, I would expect the blue (inner side of wobble) to freeze for the reason Iacopo suspected (wobble and spin tangential speed canceling). The red (heavy side) on the outside would be because it's the only color that goes that far out.

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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #16 on: May 09, 2024, 07:26:00 AM »

A ring half blue half yellow should look just green on a perfectly balanced top. But the outer edge should show either blue or yellow depending where the heavier side is when the top is unbalanced.
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In the broader world of tops, nothing's everything!  —  Jeremy McCreary

ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #17 on: May 09, 2024, 12:35:16 PM »

This color method of finding the unbalance is a special case of what Maxwell described with his dynamic top:



Going back the the spiral freezing effect, I'm still surprised how strong and clear it is to the naked eye. I need to do some slow motion video to understand it better.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #18 on: May 09, 2024, 01:12:10 PM »

Another experiment with the spiral:

I made a dotted spiral. The added weight is in front of the third dot from above.
That dot makes the largest circular trajectory, while the top spins, as it can be seen in the photos below.
The dot in the opposite position, (the third from below), which is in front of the light side of the top, is the one that makes the littlest circular trajectory. 



What I like of this method is that it is simple, it is not necessary to have other devices like brush and paint or a laser, you just spin the top, look at the stem, and soon know where is the heavy side if there is unbalance.
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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #19 on: May 09, 2024, 03:58:14 PM »

Excellent Iacopo!
You combined a kind of Maxwell color method with elements of the spiral effect that ta0 observed to a very elegant method for finding the unbalance in a top without many tools and even without the need for different colors.
Do you have already enough experience to judge the precission of this method in comparison to other methods you make use of?

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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #20 on: May 09, 2024, 04:48:09 PM »

Do you have already enough experience to judge the precission of this method in comparison to other methods you make use of?

I have to test it, I think it is less accurate than the paint and brush, but good enough anyway.
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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #21 on: May 09, 2024, 05:04:40 PM »

Excellent!

You can see, specially on the last photo, that the spot traces are brighter a one point on the circle that they follow. If you join the brightest spots, you reconstruct the spiral.

If you watch something going around an opaque circle from a point far away in the same plane, the transversal velocity is half of a sinusoidal: at the edges it's zero because it's traveling towards or away from you and at the center is maximal (equal to it's true velocity). This effect might be adding to the velocity cancellation effect so as to freeze the spiral.
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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #22 on: May 10, 2024, 01:11:19 PM »

Iacopo: You have a top where you can change the height of the center for mass so it changes from oblate to prolate and the lean would change from the heavy side to the light side. You should see this change reflected in the spiral dots.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #23 on: May 10, 2024, 03:58:54 PM »

Iacopo: You have a top where you can change the height of the center for mass so it changes from oblate to prolate and the lean would change from the heavy side to the light side. You should see this change reflected in the spiral dots.

Yes, I am sure that it would work in that way.
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #24 on: May 10, 2024, 04:23:02 PM »

You can see, specially on the last photo, that the spot traces are brighter a one point on the circle that they follow.

I had to think for some time why this happens.
I made a video in slow motion and it turns out that the bright spots in the photos are the places where the dots stay for a longer time, due to the combined motion of spin and wobble. I show it below.

I tried a dashed spiral; the heavy side is in front of the orange dash, (the first one from above, orange in the video but brown in the photos). The green dash is the light side.



In the video below you can see how the orange dash, (heavy side), makes the larges circular trajectory, while the green dash, (light side), makes the littlest circular trajectory, and how the other dashes stay for more time in the points where in the photos there are the brighter spots:

https://youtu.be/xMz_PTsBkqs

« Last Edit: May 10, 2024, 04:38:55 PM by Iacopo »
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ta0

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Re: Mysterious optical effect of spiral on stem
« Reply #25 on: May 11, 2024, 12:30:43 AM »

Beautiful work!

This Saturday I should have time to do some experiments myself.
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ortwin

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Re: Mysterious optical effect of spiral on stem
« Reply #26 on: May 11, 2024, 07:26:09 AM »

I can already see some future Simonelli tops with precious insets in the stem that spiral upwards..
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Iacopo

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Re: Mysterious optical effect of spiral on stem
« Reply #27 on: May 11, 2024, 04:08:27 PM »

I can already see some future Simonelli tops with precious insets in the stem that spiral upwards..

There are good chanches that I will do it...
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