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Welcome Dr William McGlinn

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James9118
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Welcome Dr William McGlinn

#91

Post by James9118 »

Hi Vince,

As you know I've posted the same experiment that shows the exact opposite to your video, i.e, a relatively early movement of the 'fly' end. Your video shows a late movement forward of the nylon piece.

Friction in real terms is not constant. In such a case as in chain bead experiments, friction will reduce quite dramatically once motion starts.

Cheers, James
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Walter
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#92

Post by Walter »

gordonjudd wrote: Walter,
I am not sure of the point your are trying to make but how would you compute the speed of an object that was moving along some curved path?

I would do it by setting it equal to sqrt(x_vel.^2 + y_vel.^2), and I think if you did the comparative calculations you would find the ds/dt calculation would give you the same value as taking the square root of the sum of the squares. Pythagoras was on to something don't you think?

Gordy
Gordy,

Yes, Pythagoras was on to something. It was called two dimensions and I was hoping the reference to Pythagoras would have twigged more than just his name for you.

The problem with your train analogy, which you keep sticking to whether you realize it or not, is that is essentially a one dimensional model. It doesn't matter what shape the track is as long as the train is constrained to follow the track for it's full length you have just taken a one dimensional model and added some wrinkles to it. If you pull one end of the train the entire train follows along at the same speed. There is no way it can be different. Given your curves the direction for each car of the train may be different but the speed is the same.

Pythagoras would have taken a different approach. He would have constrained only the end points to follow the track. The rest of the train would be free to follow whatever path between those two points.

Let's take a simple view of what Pythagoras would have used as an example. I am going to get rid of cars, flexibility, whatever. Imagine I have rigid 13 foot rod. I can't stretch it, I can't compress it and I can't bend it. I am going to constrain only the end points to the stay on the track. No points in between are constrained to follow the track. Now if I go trundling along the X axis the entire rod and every bit of the rod will be moving at the same speed (and direction). Now let's imagine that at the origin the head of the rod takes a right turn and follows the Y axis while the tail end is constrained to continue along the X axis until it too gets to the origin and then it can follow the Y axis as well. According to you the entire rod would continue along at the same speed. How can it not? How can different points on the bar possibly be travelling different speeds? There is no slack, there is no compression, there are no weird shapes. But what we will find (using sqrt (a^2 + b^2), otherwise known as Pythagoras), is that when the head of the rod has travelled 5 feet along the Y axis the tail end is still 12 feet from the origin. Recall that the rod is 13 feet long so when the head was at the origin the tail must have been 13 feet away. So in the same amount of time that the head travelled 5 feet the tail travelled 1 foot. Its average speed was 1/5th of what the average speed of the head end was.

Okay, the fly line is not a rigid object so it can bend into any shape and what we see during a fly cast is that when the rod tip begins to veer from the X axis that the fly end tends to continue along its current path for quite some time. The line doesn't stretch. In some cases it can compress leading to slack but typically what we see is a smooth curve from rod tip to fly. Not a straight line but not something constrained to follow the exact same path as the rod tip. It's somewhere between your train tracks and Pythagoras which means that the fly end and the rod tip end are not constrained to move at the same speed and changing the direction of the rod tip (adding a Y component to its direction of travel), even though its total speed may be increasing, may or may not result in an increase in the speed of the fly.
"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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VGB
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#93

Post by VGB »

Hi James

I remember your video and couldn't replicate it, I also produced an effort that wound back the friction element

https://vimeo.com/165879305

Just about to travel back, so will catch up soon

Regards

Vince
Casting instruction - making simple things complicated since 1765

https://www.sexyloops.com/index.php/ps/ ... f-coaching
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VGB
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Welcome Dr William McGlinn

#94

Post by VGB »

gordonjudd wrote:
The engine is pulling and the caboose doesn't move at the same time
Vince,
Do you think there might be a difference between your static example (i.e. fly end is not moving), and what I am talking about where the fly is trailing behind the rod tip as the rod tip is being accelerated along its path? I do.

Lets try to compare apples to apples, and find an example where the trailing fly's velocity does not increase at the same time the rod tip speed is increasing as it goes to RSP1.

Thanks for looking,
Yes Gordy, I think that when the force is applied in a straight line that the outcome will be different to applying it in an angle:

http://www.physicsclassroom.com/class/v ... -of-Forces

Can you find an example where this is not true?

Thanks for looking

Vince
Casting instruction - making simple things complicated since 1765

https://www.sexyloops.com/index.php/ps/ ... f-coaching
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gordonjudd
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Welcome Dr William McGlinn

#95

Post by gordonjudd »

Can you find an example where this is not true?
Vince,

I think this frame grab from the bouncing bomb back cast taken from one of Grunde's high speed videos is a good example of what I have been talking about. The line image is quite faint in that photo, but I think it shows the tension in the line (that results from the fact it is being accelerated) produced a kink-free (although non-straight) line shape.

Image

This cast included a haul that produces a different situation than what I have been talking about since the line speed could be different than the rod tip speed because of the haul.

However assuming there was no haul, I would expect the increase in the tip speed that happened in this cast as the tip path started deviating from a straight line path up to this point before RSP1 (where the tip speed was maximum) also caused the fly speed to increase by the same amount even though the tip was following a curved path while the fly was following a nominally straight one.

If the tip path happened to be straight while undergoing the same speed increase I don't think the change in the speed of the fly end of the line would have been any different.

Gordy
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Walter
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Welcome Dr William McGlinn

#96

Post by Walter »

Gordy,

I still don't understand why you are struggling with this. Here as picture so we can stop the hand waving.

You are talking about the blue line - constrained to tracks - where the is a one to one correlation between head speed and tail speed. This is essentially a one dimensional model because the entire line is constrained to a fixed path.

Pythagoras would be the green line - where the correlation between head speed and tail speed is not one to one. If you slide the head of the line up and down the Y axis the only time the tail end will move at the same speed is when both ends are the same distance from the origin. That is the only time. At all other times the relationship is not one to one. The reason it is not one to one is because the points between the head and tail are not constrained to the same path as head or tail.

Fly casting would be most closely related to the red line. It is somewhere between the two boundaries (Pythagoras and fully constrained). The relationship of head speed and tail speed is not one to one because the only constraint is that only the miniscule bit of line that is adjacent to the rod tip is constrained to any path.

This is just vector addition. Velocity, acceleration, force, etc. are vectors. Speed is derived from velocity using Pythagorean theorem. It is not a linear relationship. It is based on a quadratic relationship.
TrainTracks.jpg
"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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Paul Arden
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Welcome Dr William McGlinn

#97

Post by Paul Arden »

Pythagoras loop?
It's an exploration; bring a flyrod.

Flycasting Definitions
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Walter
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#98

Post by Walter »

If you've read Dr. McGlinn's book then you realize the increase in bend in the line indicates a decrease in the tension in the line. A decrease in tension between the rod tip and fly indicates that the force, and hence, the acceleration of the fly is decreasing. As the tension decreases slack begins to form. One of the roles that the rod tip performs by deviating from the straight line path is to take up this slack. Eventually this slack manifests as the loop.

Don't you think you should move this thread to the technical analysis forum? Dr. McGlinn's week is long over and it appears he doesn't want to participate.
"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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Walter
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Welcome Dr William McGlinn

#99

Post by Walter »

Walter wrote: Don't you think you should move this thread to the technical analysis forum?
It appears this discussion has been moved to the technical analysis forum already. I thought I would add this post as a courtesy for those of us with aging eyesight or trying to follow along on teeny tiny little smartphone screens.
"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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