Conservation Of Angular Momentum (COAM)

[Merlin]

My turn to be the bad guy.

The acceleration you see Vince, is similar to the one of the sinking line alone after it has reached the rod leg, without any consideration of the floating line and density change. Do you have an explanation? I can nail that the "torque" you mention is not there, otherwise I should have found a smaller acceleration for the sinking line alone.

Merlin

[VGB]

Are you talking about your model or the real world Daniel, I would like to see the Tracker video of your cast? It is also worth highlighting that I am using a floating line, not a sink tip and see the same outcome.

Vince

[Merlin]

Vince

Maybe one day you will realize that practice and theory are complementary, not opposite. The last post from Graeme made my day in terms of time settings. The time you see on the video (some 3 to 5 seconds) does not correspond to the cast, so there is a need to set up the timing of the model to match with the one of the video. Once this is done here is what the model tells:

GH speed history.JPG (52.23 KiB) Viewed 605 times

That sounds mechanically correct and includes the change in density. Now what if I calculate the speed history of the sinking line alone as it has entered the rod leg? I do not need the floating part so I delete it, but keep the parameters as the sinking line entered the rod leg.

GH speed history sinking line alone.JPG (44.13 KiB) Viewed 605 times

There is some slight delay (model time setting) and minimal change in rate of acceleration (the important point), consequently the potential effect of density is close to nil. This is what I stated from the beginning: the acceleration is largely linked to the line, not to the density change. If I had found half of the acceleration rate by comparison to the other graphic, then I would have concluded that there is a significant effect of density change. I checked that the level of tension in the sinking line was the same than for the model with the complete line. You speak of torque but there is no burst, the change in tension affects both the bottom and the top of the loop. An extra tension at the bottom would make the loop nose decelerate, and that is not the case. The loop is not a pulley.

Merlin

[VGB]

Daniel

Maybe one day you will realize that practice and theory are complementary, not opposite.

That is the basis of V&V, marrying up the model and the real world and understanding the gaps. As far as I can see you have twiddled some parts of your model to make it line up with the real world where it didn't before, then decided that it is more real than the real world.

I do not need the floating part so I delete it, but keep the parameters as the sinking line entered the rod leg.

What parameters are kept the same? How do you intend to prove that your assumptions are correct

This is what I stated from the beginning: the acceleration is largely linked to the line, not to the density change.

No idea what this is supposed to mean

I checked that the level of tension in the sinking line was the same than for the model with the complete line. You speak of torque but there is no burst, the change in tension affects both the bottom and the top of the loop.

Obviously, you haven't actually tried this for yourself, or you would know that your statement on rod leg tension is not true. Take another look at Graeme's video and read his comment:

During the capture of these images for you Vince, I noticed that the join between sinking and running line has moved forward during this period, which is a source of slack that I didn't realise was there. That forward movement might simply be the rod leg becoming taut though.

Where is this slack in your model?

An extra tension at the bottom would make the loop nose decelerate, and that is not the case. The loop is not a pulley.

Where is your loop nose measurement, we are looking at the fly leg speed.

Just to keep it on topic, does your model replicate the lack of change of fly leg acceleration? If so, why does it not accelerate and what makes it change?

Arthur Pendragon

[Merlin]

As far as I can see you have twiddled some parts of your model to make it line up with the real world where it didn't before, then decided that it is more real than the real world.

When I saw the still of the taut rod leg at 4.176 s, I got the explanation that the former 3.57 s for the sinking line entering the rod leg was likely wrong, hence the lag I could see before (by the way I have no memory having sent something about fly leg speed to you).
Denigrating is not my favorite activity, maybe it is yours.

What parameters are kept the same?

All

How do you intend to prove that your assumptions are correct

How do you intend to prove that you interpret correctly what you feel or observe?

Obviously, you haven't actually tried this for yourself, or you would know that your statement on rod leg tension is not true. Take another look at Graeme's video and read his comment:
During the capture of these images for you Vince, I noticed that the join between sinking and running line has moved forward during this period, which is a source of slack that I didn't realise was there. That forward movement might simply be the rod leg becoming taut though.
Where is this slack in your model?

Do you want to discuss about some sag disturbed by a transverse wave? I do not think so. The tension is multiplied by about 4 as the sinking line enters the rod leg, which is sufficient to make the rod leg taut.

An extra tension at the bottom would make the loop nose decelerate, and that is not the case. The loop is not a pulley.
Where is your loop nose measurement, we are looking at the fly leg speed.

Yes, and loop nose speed is about half of that. And incidentally, the fly leg speed is not reduced at any time. So there is no torque from the bottom.

Just to keep it on topic, does your model replicate the lack of change of fly leg acceleration? If so, why does it not accelerate and what makes it change?

Did you look at the graphics above? There is acceleration in both cases. They say that change in density does not affect significantly the acceleration due to the rollover of the sinking line. The acceleration you can notice when casting is essentially due to the line (eventually its taper), not to a change in density.

I am not going anymore to answer multiple questions which the aim is to denigrate the analytical work I am doing. And anyway that is not going to change your cognitive bias.

Merlin

[VGB]

Denigrating is not my favorite activity, maybe it is yours.

Maybe one day you will realize that practice and theory are complementary, not opposite.

Maybe your account was hacked in your last post?

The tension is multiplied by about 4 as the sinking line enters the rod leg, which is sufficient to make the rod leg taut.

Now that you have noticed the line go taut and given that tension is the summation of external forces acting on the rod leg, what "parameter" causes tension to multipliy by 4?

And incidentally, the fly leg speed is not reduced at any time. So there is no torque from the bottom.

I didn't mention fly leg speed reduction. All I have talked about is the level velocity about 3.7s on the graph, followed by rapid acceleration half a second or so later.

The acceleration you can notice when casting is essentially due to the line (eventually its taper), not to a change in density.

As properties of line taper, changes of mass or density may both the AM of the loop.

I am not going anymore to answer multiple questions which the aim is to denigrate the analytical work I am doing. And anyway that is not going to change your cognitive bias.

No problem, I'll give the science book prize to Paul

Vince

[VGB]

Given the effort Graeme put into his excellent analysis, I thought it worth bringing his post from this morning to the top again. It is worth watching the video a few times to see the relationship between the events and the effect on fly leg speed.

Here is an annotated screen shot of the point where acceleration of the fly leg kicks off in earnest (as best as I can tell - it is right on one of those shitty gaps in the frames)


Acceleration.jpg

Here, the fly leg is red, the rod leg is yellow and the dashed bit is a guess for its location (it's not visible against the background.) The blue dot is the join between sinking and running line.

IMG_2041.jpeg (64.43 KiB) Viewed 531 times

Here's the same thing at 3.8 seconds, 0.37 seconds before the above screen shot:


Acceleration_t3pt8.jpg


During the capture of these images for you Vince, I noticed that the join between sinking and running line has moved forward during this period, which is a source of slack that I didn't realise was there. That forward movement might simply be the rod leg becoming taut though.

IMG_2042.jpeg (47.32 KiB) Viewed 531 times

Here's a video of that part of the cast with the progression of the marks in time on the right. Each jump is a frame on the original video.




Cheers,
Graeme

[Paul Arden]

Hey folks, this was Walter’s suggestion and it’s a good one! Can we have a summation of the topic that answers Graeme’s initial question that we can all agree upon and post as a “best answer” pls?

Thanks!
Paul

[Graeme H]

I'll make the first summation from my point of view. It'll fire up a whole new bunch of summations, but that's the nature of this thing.

Angular momentum exists in the cast, both in the fly leg and the loop itself.

Angular momentum is not conserved within the loop due to the presence of external forces acting on the loop.

The magnitude of the AM is so low as to be inconsequential in the physics of loop propagation. That is, there are factors in the physics of the loop that swamp the influence of AM in the loop, so much so that if we ignore the loop's AM, we don't significantly alter the understanding of how the loop works.

Cheers,
Graeme

[VGB]

It depends on the casters actions and line tapers, both outcomes are possible:

https://www.sexyloops.co.uk/theboard/vi ... 420#p76725