Is the cast itself a transverse wave?

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Is the cast itself a transverse wave?

Post Number:#61  Postby Graeme H » Thu Jan 11, 2018 11:50 pm

Hi Merlin,

You're in the ballpark with your characterisation of my "conception". I don't know if I fully understand the implications of your summary, but it seems okay.

The wave's vertical propagation speed can be measured from that video of my experiment. Gravity is reasonably constant throughout the world, so the wave propagation speed you see there can be replicated anywhere and measured. (My video was shot at a high frame rate so it's shown in slow motion - maybe half speed? I don't know off the top of my head.)

In any case it's not as slow as you might think and it roughly matches the velocity of any falling object. We cannot ignore gravity.

Also remember that we always throw our loop upwards during the cast to counteract the line's decent. We may not do it consciously, but it's there. Look for it in any video of a medium distance cast. The trailing loop is a visible example of its effect.

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Graeme
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Is the cast itself a transverse wave?

Post Number:#62  Postby Geenomad » Fri Jan 12, 2018 1:15 am

gordonjudd wrote:
That is a good point, so what is the effect of the taper on the loop velocity? In a whip wave the taper will cause the velocity of the wave to increase. Does it have the same effect for the propagation of the loop in casting?


G'day Gordy
FWIW, speaking as someone with experience in cracking a stock whip, the acceleration of the cracker at the tip of the whip to greater than the speed of sound is certainly aided by the taper but there will be no crack without pullback no matter how powerfully or in what direction the whip is "cast".

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Mark
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Is the cast itself a transverse wave?

Post Number:#63  Postby Geenomad » Fri Jan 12, 2018 1:31 am

G'day Graeme
I have slept on it but it hasn't produced a fundamental change of mind. I got lost in the latest series of posts and would be more willing to try to assimilate it all if I thought I would emerge with a better understanding of how to cast, informed by an improved conceptualisation of what's going on with the farnarkolipse.

About a year ago Aitor gave me an equation for travel velocity of the farnarkolipse being half the difference between the velocity of the fly leg minus the velocity of the rod leg. This explains to me the obvious difference between hauling and not hauling, shooting and not shooting and indeed at least some of the effects of pullback (negative V for the rod leg). I will admit, however, that I remain sceptical of it fully explaining the crack of a fly or a whip.

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Mark
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Is the cast itself a transverse wave?

Post Number:#64  Postby windknotz88 » Fri Jan 12, 2018 1:41 am

My bad brothers, my bad...
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Is the cast itself a transverse wave?

Post Number:#65  Postby Graeme H » Fri Jan 12, 2018 2:34 am

Merlin wrote:Why make things simple when you can make them more complex is a French tale, I see it has been adopted by Australia :D

It's understandable that you think this way and I find the statement interesting from my point of view. My own perspective is that I have simplified things, but before you roll about the room laughing your arse off, hear me out for a bit ... :D

As I've said a few times already, I would never try to teach people about this unless they specifically asked about transverse waves (implying they have some understanding of wave theory in the first place). I can't ever imagine a time when I would tell a student they should be trying to propagate a wave vertically by displacing their line in front of them. They'd look at me as if I were crazy and question what the hell the FFi is teaching its instructors! It is not an effective teaching framework.

When I'm casting and teaching, I'm considering the line as a projectile, composed of (dare I say it) discrete elements. Aim as many of them at my intended target as possible and the fly will follow. I think of the acceleration of the line and the motion of the fly leg mainly in terms of Newton's Laws of Motion. Conventional wave theory explains the other behaviour of the line, but most of the time, I don't need to dwell on it. I just use it as needed.

So why am I thinking like this if I won't teach it? I personally understand a lot more about how overhead casting works when I use transverse wave theory as the "other pillar" of overhead casting physics.

Am I actually making it more complex than it should be?

An analogy that comes to mind is the way scholars "understood" the universe before Copernicus and his cronies overturned the astronomy models of the time. A "geocentric universe" model could be made to "work" with increasingly complex motions of the Celestial Spheres and very few scholars saw any need to change it. The Sun rises in the east and sets in the west, simple. The planets, their moons the and stars don't have a large effect to us on Earth and they are mainly of academic value only. (What's a comet? :) ) Why make things even more complex than they already were by adding yet another model to the mix?

Well, it turns out that the very concept of gravity is totally foreign in that model of a universe. The Celestial Spheres were a construct that prevented the development of Newtonian mechanics until the Heliocentric model was proposed. That Heliocentric model didn't change the fact that we perceive the sun rising in the east and setting in the west, but it had a profound effect on the way we understand why it does so and what determines the motion of the other objects we see. Things got much simpler to explain in a Heliocentric Model. (Kepler's prediction of the transit of Venus across the sun using gravity calculations finally killed off the geocentric model once and for all.)

The other analogy I keep in mind is the duality of light physics (waves & particles). In my everyday life, I'm more than happy to think of light as waves. Different wavelengths of light provide colour and that's pretty much all I need to know. That's fine, until I want to draw power from the PV array on my roof or use a digital camera sensor: for those to work, light must be a particle that knocks electrons out of the semiconductor crystal lattice, giving me free electricity or some temporary memories. Light is both a wave and a particle at the same time.

The latter analogy is really pretty close to how I consider casting physics. For me, fly lines have dual physics at play in each cast. The fly leg is following a ballistic model. I make the line move as a projectile with energy input and directional control. Each bend in the fly line is a transverse wave, the biggest of which is the loop and the smallest are mends. Waves can be modified with tip position, line mass and tension.

If I can't understand what's happening by applying Newtonian physics, I can usually nut it out with wave physics. In a few cases, the solution requires the application of both.

For me, it's a simpler approach than what I see on display here because I don't need to construct a Loop Wave to explain what's happening. I consider the Loop Wave as the Celestial Sphere of fly casting, preventing many people from grasping the underlying physics. The Loop Wave does not appear in physics text books: a caster can't do any meaningful research into casting physics by searching for Loop (or Fly) Waves. They will sometimes come here and ask about loops and transverse waves, and then the shit really hits the fan! :) Information about transverse, longitudinal and surface waves can all be found in physics text books, and they all occur in the fly line under different circumstances.

Taking this approach to understanding fly casting lets me gain a good working understanding of concepts like loop morphing, trailing loops, overhang, line tapers, head lengths, leader design, collapsed casts, casting into and across winds and so much more. I get frustrated watching people here attempting to explain a morphing loop or a trailing loop using the Loop Wave as the starting point, knowing that if I try to explain using a transverse wave model, it will just fly over everyone's head. It would be like explaining gravity to the contemporaries of Copernicus - the concept has no foundation in the collective understanding.

So, back to your question Merlin: "Why make things simple when you can make them more complex?" It only appears to be more complex when viewed through a Celestial Sphere.

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Graeme
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Is the cast itself a transverse wave?

Post Number:#66  Postby Graeme H » Fri Jan 12, 2018 2:46 am

Geenomad wrote:Have to say you are wearing me down on the nature of the loop. Hard to visualise vertical propagation and horizontal displacement in a horizontal line when the medium itself is moving horizontally. My intuition is pricked however. Will sleep on it. :D
-------------------------------------------------
G'day Graeme
I have slept on it but it hasn't produced a fundamental change of mind. I got lost in the latest series of posts ...

That's okay Mark. It's not really that important unless you're trying to answer certain questions (such as "What was Berlin on about?")

If all you're really chasing is a visualisation of vertical propagation and horizontal displacement, go back to the video I made. It's clear that the waves are moving downwards while the line is moving sideways.

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Graeme
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Is the cast itself a transverse wave?

Post Number:#67  Postby Paul Arden » Fri Jan 12, 2018 6:36 am

Sorry I've been fishing, getting married and so on, but I have been following this thread!

The purpose of defining something as a Transverse Wave is measure it? How does loop propagation look when it comes to using the maths?

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Is the cast itself a transverse wave?

Post Number:#68  Postby James9118 » Fri Jan 12, 2018 7:35 am

It looks like this:

https://www.facebook.com/10000607237692 ... 6072376926

(Don't know how to upload a GIF here - maybe because it has a .MP4 extension?)

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Is the cast itself a transverse wave?

Post Number:#69  Postby Paul Arden » Fri Jan 12, 2018 7:54 am

I'll have a look at Board extensions tonight, James!
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Is the cast itself a transverse wave?

Post Number:#70  Postby James9118 » Fri Jan 12, 2018 8:49 am

Paul Arden wrote:I'll have a look at Board extensions tonight, James!


Be careful though - allowing video uploads to your server could lead to volume issues.
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