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Conservation of Momentum

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Walter
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Conservation of Momentum

#221

Post by Walter » Mon Jul 15, 2013 1:45 pm

Merlin wrote:Aitor
You just forgot to put in bold the assumption. I can shoot some line too, and I know that the loop keeps on rolling because of the friction of line in the guides.
I am still amazed by the fact that one keeps on speaking about COM as several people explained there was none.
What ca we say more?
Merlin
None, as in it doesn't exist as Gordy says?

With respect to the loop unrolling because of friction between the line and the guides I think you should take the time to look at the videos posted by Lasse, Bernd and Aitor.
"There can be only one." - The Highlander. :pirate:

PS. I have a flying tank. Your argument is irrelevant.

PSS. How to generate a climbing loop through control of the casting stroke is left as a (considerable) exercise to the reader.

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Conservation of Momentum

#222

Post by Unregistered » Mon Jul 15, 2013 2:04 pm

Paul Arden wrote:I don't think you understand copyright. You don't choose to make stuff copyright; it automatically is. You can't republish articles, books, magazines, even web pages, without the author/publisher's permission.
Yes, I understand copyright, in fact I have some copyrights of translations I made.

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Conservation of Momentum

#223

Post by Unregistered » Mon Jul 15, 2013 2:09 pm

Merlin wrote:Aitor
You just forgot to put in bold the assumption. I can shoot some line too, and I know that the loop keeps on rolling because of the friction of line in the guides.
I am still amazed by the fact that one keeps on speaking about COM as several people explained there was none.
What ca we say more?
Merlin
Merlin,

Since you never take the time to look at the material provided by others you don't know that there are some videos that show a loop propagating without any line on the guides: no line = no friction.

I am still amazed by the fact that some people seems to be trying to have a debate while giving a fuck about other's arguments and visual proofs.
What can I say? Sexyloops style at its best. :closedeyes:

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Merlin
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Conservation of Momentum

#224

Post by Merlin » Mon Jul 15, 2013 2:34 pm

My smartphone does not allows me to see all videos, but I trust what you say. Was the rod length long or short? I shall have another try. I would suspect that rolling over is easier with a short rod length: less inertia to overcome.

Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

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Graeme H
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Location: Perth, Western Australia

Conservation of Momentum

#225

Post by Graeme H » Mon Jul 15, 2013 2:36 pm

Well, I've now filmed the experiment and the result is here (Sorry, I don't know how to get the video to embed in this software …)

The hypothesis I'm attempting to support is that the line's constant velocity (and thereby, its momentum) at the time the rod stops and tension in the rod leg are the main factors that initiate and propagate a loop and hence complete the cast.

The method I've used is to create a situation where the fly leg has a measurably constant state of motion and tension in the rod leg is easily demonstrated.

What you're seeing initially looks like a "normal cast". In fact, it's simply the line laid straight on the road from the end of the rod tip and the rod tip then pulled back along the axis of the fly leg. When the camera is moved with the rod tip so that all movement is seen relative to the tip, the experiment demonstrates that tension in the rod leg is all that is required to initiate and propagate a loop, and that the loop is maintained until the fly leg disappears.

Just before Stage A, the line is in tension. (In the experiment, the tension is opposed by drag on the road.)

When the tip stops, the line maintains its state of motion. (In the experiment, it lays "motionless" on the road, but that is a constant state of motion. All line outside the tip has the same velocity as the rod tip at this point.)

When the tip is held stationary, the line continues with its constant state of motion and a loop initiates. (In the experiment, the tip begins moving back long the road, which means the line is now moving forward relative to the tip.)

As the line continues to move forward relative to the tip, tension in the rod leg causes the fly leg to cease the forward motion of the fly leg and a loop is formed. (In the experiment, the line is being dragged back along the road by the tension in the rod leg.)

The fly leg continues moving forward at a steady velocity until the fly leg disappears and the cast is complete. (In the experiment, the line is dragged into the rod leg as I walk backwards along the road. The fly leg remains stationary on the road, however, relative to the rod tip, it continues to move forward at walking pace.)

With the experiment complete at this point, the "cast" appears to be a normal cast when shown at speeds approaching those we are used to. When it's "slowed down" to actual speed, it's easier to see what happens in reality. This is one instance where using a moving frame of reference helps to clear up some of the questions. (At least, it does for me. I'm sure others will not agree. That's fine - I'm not going to argue the point.)

This is an easy experiment to replicate by anyone with a fly line, a rod and a carpet or nearby road. Concentrate on the rod tip, watching the line with peripheral vision to focus in that frame of reference. You'll see the line unroll just as it does in a normal cast. Then flick the line along the road too and notice the similarity between the two "casts".

----------------------------------------------------

If I had fed line off my reel at the same speed as I walked (as if I were shooting line in a cast), the loop would not have continued to propagate. Without tension in the rod leg, the rod leg has the same velocity as the fly leg and the loop stops. (In this example, I'm ignoring rotational momentum within the loop. I believe it is inconsequential compared with the other forces in play.)

If I had fed line out at a speed less than my walking speed, the loop would still propagate. While there is a difference between the velocities of the rod and fly legs, the loop will move along the line.

If we were to cut the line after the loop had been initiated and while the line was shooting, both the fly leg and the rod leg would have velocities. Newton told us that those velocities will be maintained because there are no (substantial) external forces acting on either leg. (If the fly leg were moving forward at 3m/s and the rod leg at 1m/s, both would continue at that rate, and the loop would move forward at 1m/s relative to the rod leg.) This is clearly shown in earlier videos.

Sorry for the long post. It takes more than 2 sentences to explain some things though. :)

Cheers,
Graeme

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Conservation of Momentum

#226

Post by Unregistered » Mon Jul 15, 2013 3:07 pm

Merlin wrote:My smartphone does not allows me to see all videos, but I trust what you say. Was the rod length long or short? I shall have another try. I would suspect that rolling over is easier with a short rod length: less inertia to overcome.

Merlin
The rod was green.
I don't give a fuck either, Merlin.

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Conservation of Momentum

#227

Post by Unregistered » Mon Jul 15, 2013 3:11 pm

Paul Arden wrote:Anyway, I've already sent you a copy :p

Cheers, Paul
Anyway I have received nothing :)

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Conservation of Momentum

#228

Post by Unregistered » Mon Jul 15, 2013 3:25 pm

Merlin wrote:
Aitor
I am still amazed by the fact that one keeps on speaking about COM as several people explained there was none.
What ca we say more?
Merlin
By the way, I have not discussed about conservation of momentum for the last weeks, just about the reason for a loop to propagate when there isn't any force applied by the rod or the caster.
There are a good number of videos proving that propagation, Lasses's ones are very good.

First the objection from Gordy was that it is impossible to happen, that the first video uploadd by Lasse years ago was no proof because the line (the yarn of an MPR) touched the ground before completing unrolling.
More than two years ago I shoot a video of Bernd showing the same untethered propagation without the yarn touching the ground. I didn't upload it because it would be useless: some people see just what they want to see and nothing else; others just don' watch.

After those first experiments Lasse has shot a good number of examples with actual fly lines for everybody to check. I provided another video showing the same phenomenon. But they all are worthless, I know.

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Merlin
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Conservation of Momentum

#229

Post by Merlin » Mon Jul 15, 2013 3:32 pm

Interesting approach Graeme, but could it really match the videos when the rod leg is released (at last I have seen a couple of them)?
Imagine we release the rod leg (videos), then the rod leg speed cannot reach immediately the fly leg speed because of its inertia, unless the rod leg is really tiny which is imossible to control in practice. The loop would freeze only if the rod leg can get speed quickly. In the bed chain experiments it seems to be possible but not in the fly line experiments, as shown by the videos and in that case the loop rools over until both legs get the same speed which is achieved when the line is straight (quite an obvious situation).
As long as the legs have different speeds the loop rolls over. I had the gut feeling that it would not take long for the rod leg to speed up but this is not the case. If I can find the time I shall try to model that properly, just to see if there are some critical features that drive the phenomenon.
So sorry for missing the videos. Now the question is what is the tension in the line during the fly of the free line?
May I recommend to keep cool and relaxed, we are not in the schoolyard.
Merlin
Fly rods are like women, they won't play if they're maltreated
Charles Ritz, A Flyfisher's Life

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Conservation of Momentum

#230

Post by Unregistered » Mon Jul 15, 2013 3:35 pm

Merlin wrote: May I recommend to keep cool and relaxed, we are not in the schoolyard.
Merlin
Exactly. I pretending to be in a friendly exchange of ideas without actually taking into account other's arguments is more proper of a schoolyard.

Cheers.

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