Magic Spheres

  • #1
Look at this experiment: Why roll the balls after the collision back to each other? Are they magnetic?
 

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  • #2
DaveC426913
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Spoiler! Highliight to read:

The balls are quite dense. They are running on rails, which means they are rotating much faster than their movement would indicate. There's a lot of angular momentum stored.
That angular momentum is not lost when they collide and bounce off each other. In effect, as they move apart, they are "skidding" - they've lost traction, but are still rotating. Eventually the rotation gains traction on the rails and the spheres accelerate toward each other again.


Reviewing the video again, I can see confirmation that I am right. The balls are not perfect; there is an arrow marked on each of them which shows how they are rotating. You can see the arrows in the closeup (as a matter of fact, you can juuuust catch them at the start of the closeup - at 0:19 juuuuust as they disappear into the black reflection at the bottom.) They are rotating the same direction both before and after the collision.
 
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  • #3
Danger
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Gee, that's complicated. I would have just filed a low spot in the rail. :biggrin:
 
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  • #4
DaveC426913
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:D The first post I made, which I deleted as superfluous, suggested the rails might simply be bowed in the center. But after more examination, I decided the demo was legit, not just a trick.
 
  • #5
Danger
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You're probably right. My eyes aren't that good any more; I can't really see the spin.
 
  • #6
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Hard to say without more data. Is it certain that balls/spheres are made homogeneous ?
 
  • #7
A.T.
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I can't really see the spin.
Look at the sky reflection, right when they collide.
 
  • #8
A.T.
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Is it certain that balls/spheres are made homogeneous ?
The density distribution seems symmetrical, given how uniformly they roll.
 
  • #9
Danger
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Look at the sky reflection, right when they collide.
Okay, I've got it now. When I first looked at it, that arrow thingie just didn't quite register in my brain. It took half a dozen more viewings before it did. (I saw it; I just couldn't figure out what it was doing.) Maybe temporal dyslexia affects visual things as well as spoken ones. :redface:
 
  • #10
RonL
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I'm not sure why I only saw the arrows appear one time ?
 
  • #11
Danger
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I'm not sure why I only saw the arrows appear one time ?
Maybe there's sidespin as well, so they weren't in a visible spot earlier. Originally, once I realized that they were arrows, I suspected that they might have been digitally added to indicate spin, but that doesn't seem to be the case.
 
  • #12
A.T.
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I'm not sure why I only saw the arrows appear one time ?
Because they cross the upper bright part only one time. But you see them also at 0:17 on the left ball, in the lower right part.
 
  • #13
RonL
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Because they cross the upper bright part only one time. But you see them also at 0:17 on the left ball, in the lower right part.
Thanks, yes:)
 
  • #14
DaveC426913
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Did no one read my spoiler? It describes the arrows.
 
  • #15
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Did no one read my spoiler? It describes the arrows.
I just read the OP's "are they magnetic?", watched once, then read your spoiler, then watched again and it all made sense.

Once I realised the balls were rolling on rails the dramatic pushes and attractive reactions all fell into perspective.
 
  • #16
Danger
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Did no one read my spoiler? It describes the arrows.
I read it, and once I actually realized that they were physically present as opposed to CGI it made sense.
 
  • #17
RonL
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I can't understand what highlight to read, is supposed to do ?
Your next post said you deleted the first one.
Now you ask if no one read it ? I'm confused other than to say post #4 you say it's not a trick o_O:)
 
  • #18
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I can't understand what highlight to read, is supposed to do ?
I didn't get it at first either, just click and drag the mouse like you are selecting text to copy or quote.
 
  • #19
RonL
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I didn't get it at first either, just click and drag the mouse like you are selecting text to copy or quote.
Thanks, I finally figured it out :) I'm pretty simple minded when it comes to finding text that's not visible. :D
I did slide the mouse on the text that was visible and all that came up was +quote or reply :oops:
 
  • #20
Spoiler! Highliight to read:

The balls are quite dense. They are running on rails, which means they are rotating much faster than their movement would indicate. There's a lot of angular momentum stored.
That angular momentum is not lost when they collide and bounce off each other. In effect, as they move apart, they are "skidding" - they've lost traction, but are still rotating. Eventually the rotation gains traction on the rails and the spheres accelerate toward each other again.


Reviewing the video again, I can see confirmation that I am right. The balls are not perfect; there is an arrow marked on each of them which shows how they are rotating. You can see the arrows in the closeup (as a matter of fact, you can juuuust catch them at the start of the closeup - at 0:19 juuuuust as they disappear into the black reflection at the bottom.) They are rotating the same direction both before and after the collision.
I believe this man is right. ( and I didn't say that because he looks like moses.)
 
  • #21
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In the impact, the spheres exchange momentum but no angular momentum. Therefore a slipping phase follows after the impact until the spheres can roll without friction.

Hier you can find an explanation in German;
 

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