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## Analysing loop propagation 2

Moderator: Torsten

Torsten
Posts: 194
Joined: Tue Jan 22, 2013 7:34 pm

### Analysing loop propagation 2

OK guys, we'll try to answer Paul's question again.

Please this time without lengthy, long-winded discussions about waves or about the term "loop"! In focus are now the other concepts.

Paul:
Something I seem to recall reading here was that there are many ways to analyse loops. Such as momentum (/change) being one. Another would be to look at the energy in the cast. A third would be to consider the loop to be a wave.

Since it’s the same loop I assume that the result of the analysis would be the same using each method. I also remember reading that we choose the simplest method as opposed to wave propagation for example which for an untethered end is rather complex?

Do I have this right? If so does anyone use two methods to check the analysis? And finally is anything lost in one method that another method might help explain? Dolphin Nose for example.

Bianchetti Ivan
Posts: 164
Joined: Wed Sep 30, 2015 8:25 am

### Re: Analysing loop propagation 2

My interpretation as a simple ignorant, I don't think it's propagation, but I think it's contrast, that is, the upper part travels in speed, the lower part contrasts it, being stronger the part below the energy tends to be consumed by the most resistant part by subtracting it from the weakest, practically the loop is the part where it slows down when falling.

Graeme H
Posts: 1930
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation 2

Good luck.

Cheers,
Graeme
FFi CCI

Paul Arden
Posts: 13901
Joined: Thu Jan 03, 2013 11:20 am
Location: Belum Rainforest
Contact:

### Re: Analysing loop propagation 2

Hi Guys,

I actually got my answer quite quickly
viewtopic.php?f=11&t=3346&start=10#p55511 From Merlin and viewtopic.php?f=11&t=3346#p55509 from Dirk. True the discussion moved to the concept of whether indeed waves were helpful, and I think we’ve seen the results of that line of thought

How about you, Torsten? How do you decide which approach is best to analyse loop phenomena?

I will add for me anyway, that thread gave me a pretty solid insight into why waves would not be the preferred analytical approach. Which has probably been more useful than the original question

And to be perfectly honest, I started the discussion to see where it would go

Cheers, Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

Torsten
Posts: 194
Joined: Tue Jan 22, 2013 7:34 pm

### Re: Analysing loop propagation 2

How about you, Torsten? How do you decide which approach is best to analyse loop phenomena?
I'd do a "market research" first, collect papers, principles etc. What we like to do then in our company for example is then to construct a decision matrix - this can be helpful for a better, more objective choice.
https://en.wikipedia.org/wiki/Decision_matrix
https://toggl.com/blog/decision-matrix

First we should define what we mean by "analysing loop propagation" - Do we want to understand an actual cast by means of video analysis and similar tools or do we want to get a better general understanding of the physics behind it?

I'd like list principles, properties that we can use. I think Wikipedia is good enough for the definitions, also sometimes you can find nice video clips on Youtube about physics, so I'll link that. Let's start:

Classical mechanics
https://en.wikipedia.org/wiki/Classical_mechanics

Limits of validity
https://en.wikipedia.org/wiki/Classical ... f_validity

-> We're talking only about classical mechanics and can ignore anything else, because of the dimensions and velocity of the fly line.

Newton's laws of motion
https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion

Mass
https://en.wikipedia.org/wiki/Mass

Momentum
https://en.wikipedia.org/wiki/Momentum

Velocity
https://en.wikipedia.org/wiki/Velocity

Acceleration
https://en.wikipedia.org/wiki/Acceleration

Force
https://en.wikipedia.org/wiki/Force

Tension
https://en.wikipedia.org/wiki/Tension_(physics)

Energy, Work
https://en.wikipedia.org/wiki/Energy
https://en.wikipedia.org/wiki/Work_(physics)

Euler's laws of motion
https://en.wikipedia.org/wiki/Euler%27s_laws_of_motion

* these extend Newton's laws of motion for point masses to rigid body motion
* NOTE the fly line is *not* a rigid body, so you need to be careful, when you're using terms like angular momentum.

Angular velocity
https://en.wikipedia.org/wiki/Angular_velocity

Angular momentum
https://en.wikipedia.org/wiki/Angular_momentum

Torque
https://en.wikipedia.org/wiki/Torque

I think we can describe a fly line already well with Newton's laws and concepts like mass, momentum, velocity, acceleration, force, tension, energy.
Euler's laws with concepts like angular momentum are maybe useable but the is not a rigid body (but can be approximated by a combination of multiple rigid bodies).

Lagrangian mechanics
https://en.wikipedia.org/wiki/Lagrangian_mechanics

* This is a mathematical reformulation of classical mechanics, an energy based approach
* Daniel and I have used it for some computations

More tomorrow.

Paul Arden
Posts: 13901
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Location: Belum Rainforest
Contact:

### Re: Analysing loop propagation 2

Thanks Torsten.

For several years there has been some arguments about the fundamental driver/s behind loop propagation, as you’ll know, and some surprisingly strong feelings have emerged (Emotional attachment to physics arguments is way beyond me by the way!)

Now since this runs to the very core of “how a loop unrolls”, despite the continual pram fight, I actually think we are doing a disservice to everyone by not resolving it. It’s all very well to try to figure out how a dolphin nose appears but if we can’t put to bed the simple question as to how the basic loop unrolls then I think there is a problem.

Broadly speaking, there are those who think that the fly leg is in flight and that this is why it rolls over and there are others who say that the fly leg is being pulled along by the front of the loop (momentum change resulting in a force). When I mentioned this to you some time back I said I thought it might be both (reasoned because 1. when a loop hits a wall the entire fly leg runs into it and 2. the loop chain drop experiment off a wall in free fall reaches the ground before a non loop). Personally I think it’s mostly in flight with a little bit of pull, but that’s largely irrelevant because the only thing I know about Lagrangian mechanics is how to pronounce it and I’m not even certain about that.

Anyway it wasn’t possible for me to moderate these discussions which is probably why they descended into chaos. And the reason it wasn’t possible is because I don’t have the physics hammer - I dropped out of that 30 years ago to go fishing and I’m still out there.

James’ opinion is that the loop propagates because the fly leg is in flight and the loop front has angular momentum (I believe angular momentum in this case is actually conserved). So he has two parts, unfortunately not everyone, or even anyone, seems to agree.

How are we going to resolve this issue? It doesn’t make sense to me that the fly leg is simply in flight, but it doesn’t make sense that it is simply being pulled along either. There is rigidity to the loop that IMO can only come from an acceleration. Also when the loop stops unrolling it dies a fluttery death rather quickly.

It’s been what, 20 years since you first calculated the Spring/Lever ratio 17/83%? Maybe you could do something along the same lines with push me/pull me, or at least try to help find resolution to this core issue.

I can help by providing biscuits and beer.

I know you are flat out busy and I don’t expect it now. Maybe it’s something we can muse about for the future?

Thanks Torsten.

Cheers, Paul
It's an exploration; bring a flyrod.

Flycasting Definitions

Paul Arden
Posts: 13901
Joined: Thu Jan 03, 2013 11:20 am
Location: Belum Rainforest
Contact:

### Re: Analysing loop propagation 2

Ok I didn’t know how to pronounce it.

Incidentally if anyone else is going to watch part 1 then part 2 is essential!

[media] [/media]
It's an exploration; bring a flyrod.

Flycasting Definitions

John Waters
Posts: 878
Joined: Mon Jan 14, 2013 9:16 pm

### Re: Analysing loop propagation 2

Interesting as always Gents, I must have missed it but in a nutshell, what causes the dolphin nose and is the cause the result of rod movement?

John

Graeme H
Posts: 1930
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation 2

I'd like someone to explain why the angular momentum in the loop disappears when the tension in the rod leg is removed.

That should be a simple one.
FFi CCI

Graeme H
Posts: 1930
Joined: Fri Jan 25, 2013 2:54 pm
Location: Perth, Western Australia

### Re: Analysing loop propagation 2

Torsten wrote:
Sat Oct 17, 2020 8:26 pm
First we should define what we mean by "analysing loop propagation"
I agree with this. Maybe we should begin with a definition of propagation:
The act or process of propagating, especially the process by which a disturbance, such as the motion of electromagnetic or sound waves, is transmitted through a medium such as air or water.
Would someone like to reframe the question of analysing loop propagation without using the word "propagation?" Since we're now excluding discussion of waves but keeping an open mind to all other possible explanations, the thread title no longer seems appropriate.

Cheers,
Graeme
FFi CCI