Is the cast itself a transverse wave?

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Is the cast itself a transverse wave?

Post Number:#111  Postby Paul Arden » Fri Jan 19, 2018 12:45 pm

Sorry for three posts, and not one single one - I try not to do this.

For many years Graeme I used to practise my carry standing on the roof of my 4x4 parked on the edge of a cliff overlooking the Waiau River, SI, NZ. From this position I could carry 105ft of MED and have the time and space to really shape loops. I would often deliver my forward cast at an angle below the horizontal. The interesting thing about this exercise was of course loop shaping, but I made the observation that the loop would fly out without (noticeable) free-fall, and having unrolled would then very obviously free-fall.

I'm not in the position to video this at the moment, but I can imagine that standing on the bridge at Banding Island will produce a similar result and I can video this next month. In the meantime if I can find somewhere similar here in Tassie I will film it.

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Is the cast itself a transverse wave?

Post Number:#112  Postby Graeme H » Fri Jan 19, 2018 1:59 pm

No probs Paul.

Seismic surface waves are one example of surface waves. Not all surface waves are seismic waves though. From the reference I posted with that image before, a surface waves is defined by the motion of the particles:

In a surface wave, particles of the medium vibrate both up and down and back and forth, so they end up moving in a circle.

Image

These can occur in any medium, most often in water and on the surface of the earth after an earthquake.

I can't quite picture the cast but are you pulling the line towards the target at any time during the cast? (Actually, it sounds a lot like that curve cast I was demonstrating on the river on the Sunday. Off track back-cast followed by a low side cast with a flick of the wrist to drive the loop over the top of the tip.)

I expect standing high up and having clear air below on the back and front cast would be quite mesmerising. It also means you can cast straight out without the line hitting the ground and carry much more line than otherwise. It works because you can let the (say) BC fall lower before hitting the front cast with a higher trajectory than you could ever do on land or water. You can't aim that FC up high enough if the BC hits water/grass. The launch angle is too low to give you the desired result. You need to throw it upwards to reach right out.

The line progression appears weightless because the fly leg (the projectile) is consumed by the loop before it falls below the loop. It's an optical illusion of sorts because we only watch those wonderful loops move away at half the speed of the line we threw.

The fly leg still falls though. It must because gravity always sucks. :)

A "Loop-centric" model for casting requires very complex equations to explain what we see. Even so, the model has many inconsistencies.

A projectile motion model is pretty simple to model using high school level physics. Swap the fly line for a lure on the end of the same rod and there is no doubt it's a simple projectile, but attach a fly line and we're suddenly flummoxed.

We throw line, not loops. Loops only form after we finish throwing the line.

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Is the cast itself a transverse wave?

Post Number:#113  Postby Paul Arden » Fri Jan 19, 2018 2:26 pm

I thought you threw waves?
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Is the cast itself a transverse wave?

Post Number:#114  Postby Graeme H » Fri Jan 19, 2018 2:55 pm

The two concepts are not mutually exclusive. We get a wave in a slinky by throwing the spring sideways from where it's stretched to. Waves are the result of displacing the pieces of a medium. Little pieces of something all joined together.

As I said way back when, I never mention transverse waves unless someone specifically asks about them. We (or at least, I) teach them to cast a fly line. When I cast, I think of it as throwing the line as smoothly as I can through the narrowest tunnel I can. It's much easier for me to teach others to throw a line than the abstract concept of a wave.

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Is the cast itself a transverse wave?

Post Number:#115  Postby Lasse Karlsson » Fri Jan 19, 2018 3:29 pm

Me too Graeme :cool:
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Is the cast itself a transverse wave?

Post Number:#116  Postby gordonjudd » Fri Jan 19, 2018 4:23 pm

No magic up my sleeves. It's just simple Newtonian stuff.

Graeme,
I think when you actually study the papers on the subject, you will find that the propagation of the loop is not so simple.

You are making the typical mistake of applying the physics we learn in high school that deals with simple point masses, and misapplying it to the much more complicated physics of distributed masses and viscoelastic media.
Can someone point out how air drag lifts a falling object please?

Drs. Gatti-Bono and Perkins provided that answer in a short note years ago.
effect of loop shape on drag induced lift of fly line
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Is the cast itself a transverse wave?

Post Number:#117  Postby VGB » Fri Jan 19, 2018 4:42 pm

I'll go with the loop being a wave when it is demonstrated that the fly cast meets the wave equation and I'll believe in lifting loops when I see an elephant fly.

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Is the cast itself a transverse wave?

Post Number:#118  Postby Merlin » Fri Jan 19, 2018 5:17 pm

Vince

On top of the paper Gordy mentioned, there are two other ones from Noel which I shall send you.
I confirm that elephants do not fly but also that « lift » (or said differently drag forces acting against gravity) do exist.

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Is the cast itself a transverse wave?

Post Number:#119  Postby Merlin » Fri Jan 19, 2018 5:21 pm

Tomorrow I shall show you that a point in the line does not have a ballistic trajectory.
:ninja:

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Is the cast itself a transverse wave?

Post Number:#120  Postby VGB » Fri Jan 19, 2018 5:31 pm

Merlin wrote:Vince

On top of the paper Gordy mentioned, there are two other ones from Noel which I shall send you.
I confirm that elephants do not fly but also that « lift » (or said differently drag forces acting against gravity) do exist.

Merlin


Merlin

Thank you, I look forward to receiving them. As an aerosystems engineer, I am aware on a day to day basis that lift can act against gravity and that by convention, drag is defined as being parallel to the free stream flow. Therefore, drag and lift are at 90 degrees to each other because lift is defined as the component of aerodynamic force that acts perpendicular to the flow direction. We really shouldn’t be in the business of rewriting established conventions.

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