[GH] Walter,
If you really want to see some effects of gravity on casting, do as I did and cast leaning over a high balcony with the rod plane inverted.....in the downward vertical position. Adds a new dimension.
[WS] Gordy,
I guess great minds do think alike - I've done something similar but casting upwards instead. I'm able to create an almost stationary loop this way and thus remove aerodynamic affects when exploring loop physics.
----- Original Message -----
From: Gordy Hill <
MasterStudyGroup@xxxxxxxxxxx>
Date: Monday, November 21, 2011 9:25 am
Subject: Does the line always follow the rod tip? 7
To: Walter Simbirski <
simbirsw@xxxxxxx>
>
>
>
> Walter & Group...
>
> [GH] A bit of levity helps as we confront
> controversial issues. The attachments: Moments of concern
> on the stream !
>
> Tomorrow: My summation.
>
> (After that, I'll be away for a few days celebrating our
> Thanksgiving with family and friends.)
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> [GH] From Aitor Coteron:
>
>
> If we, as Ally has pointed out, think of the line as a chain
> with a number of links we can understand all of this better.
>
> When the rod tip moves all the links of the chain start moving,
> i.e. they gain momentum. Momentum is vectorial, it has magnitude
> and direction. All the links move at the same speed but the
> difference is that not all of them move in the same direction
> (i.e. they have different velocities) so they have different momentum.
>
> Guy says that the links closer to the "rod" tip influence those
> in the chain end. He fails to see that the influence is
> reciprocal: the momentum in the chain end is also deviating the
> chain close to the rod from its trajectory. Some part of the
> chain goes in a direction different from that of the rod tip,
> and it resists to change that direction in a degree that depends
> on its momentum (in this case, since speed is the same for all
> the links, the resistance of the chain end to change its
> direction depends only on its mass).
>
> So the chain end links can not keep their original trajectory
> because the links closer the rod tip are pulling them in another
> direction; and vice-versa: the links closer to the rod tip can
> not keep going in the original direction (that of the rod tip)
> because the links in the end are pulling them away.
>
> So the line lay out we get is the resultant of those different
> vectors involved. If the resultant is a vector that points in a
> direction different of that followed by the rod tip the line
> doesn't follow the rod tip trajectory. It can not do it.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> [GH] A basic understanding of the word, "momentum" is
> important in order to properly digest Aitor's message.
>
> From Online Dictionary :
>
>
> linear momentum. Mechanics . a quantity expressing the motion of
> a body or system, equal to the product of the mass of a body and
> its velocity, and for a system equal to the vector sum of the
> products of mass and velocity of each particle in the system.
>
> As Aitor has pointed out, momentum is a vector quantity, meaning
> that it is directional along with acceleration and
> velocity. Scalar quantities such as "speed" are not directional.
>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> [GH] From Walter Simbirski :
>
> Hi Gordy,
>
> When we look at finite element analysis we consider each element
> to be a rigid body. Each of these rigid bodies is joined to the
> next rigid body by a joint that can rotate freely (and has no
> tendency to return to a straight or unloaded position) or is
> elastic in nature such that is resists bending and has a
> tendency to return to the straight position (or unloaded
> position). When we take a look at the finite elements in a fly
> line the forces that act on these elements are:
> - gravity
> - air resistance
> - the pull from the element before it in the chain of finite elements
> - the pull from the element following it in the chain of finite
> elements (this is a very significant force when analyzing the
> movement of each element).
>
> Some things to consider in Aitor's video that I haven't seen
> mentioned yet (although maybe I just missed it):
>
> - Aitor's video does not simulate the affects of gravity so the
> movement of the bead chain can only be compared to what would
> happen if the force applied by the casting stroke was much more
> significant than the force applied by gravity. This is true for
> some casting strokes but not all casting strokes.
>
> - If we look at the angle of the line relative to Aitor's
> casting stroke at the start and after the line has fully
> straightened after the stop we see that the bead chain has
> basically been flipped 180 degrees (i.e. the before and after
> positions of the line form a straight line) but with the end
> point translated by the stroke.
>
> Cheers
>
> Walter
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> [GH] Walter,
>
> If you really want to see some effects of gravity on casting, do
> as I did and cast leaning over a high balcony with the rod
> plane inverted.....in the downward vertical position. Adds a new
> dimension.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> [GH] From Mark Surtees:
>
> Hi Gordy
>
> If Ally is correct here…..
>
> Aitor’s chain converts the “line” to a series of point masses if
> you like and is a closer representation of the fact. Only when
> the line and rod tip are exactly aligned with the applied force
> will the velocities of each element be the same.
>
> …which IMO he is
>
> Then this..
>
> So to keep it simple the line always follows the rod
> tip, based on it's physical design and the conditions under
> which the cast is being made.
>
> And this…
>
> The fly line follows the path where the rod tip speeds up and stops.
>
> Can only be true when the whole line is aligned with the force
> vectors throughout the casting stroke, irrespective of design or
> conditions, something which is theoretically possible, but quite
> unlikely, up to RSP and quite plainly not the case after RSP.
>
> From a teaching perspective there is absolutely nothing the
> matter in saying that the tip path influences the path of the
> line, it obviously does and it is easy to demonstrate on the
> ground or indeed in the air how it does so. In this sense this
> sort of statement is not dissimilar to Al Crises “Zoomies” or
> “painting a rainbow” or Mels “Whuump” or dozens of others that
> we could think of, indeed, asking a student to imagine “that the
> line followed the rod tip” in order to get better control of the
> tip path is obviously a really effective way of getting the idea
> across. Nothing the matter with that whatsoever because no-one
> in their right mind is going to talk about mass distribution and
> Walters finite element analysis in an effort to get the concept
> over....it’s too complicated. The problem arises because this
> fairly uncontroversial means of communicating a concept to a
> student seems to have been converted into an absolute truth
> about the dynamics of a cast which is regularly reproduced by
> instructors as a real explanation of what is actually happening
> to the line.
>
> Ally also says this..
>
> Study of rod movement in isolation is insufficient to explain
> the outcome of a cast.
>
> Also on the nail..
>
> For me at least, a massively oversimplified absolute which says
> the line always follows the rod tip, full stop, isn’t something
> I would personally choose to use mainly because it is patently
> incorrect…asking someone to imagine something is true and
> telling them that it is true are two different things in my
> book.
>
> Mark
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> [GH] Mark,
>
> "The fly line follows the path where the rod tip speeds up and stops.
>
> Can only be true when the whole line is aligned with the force
> vectors throughout the casting stroke, irrespective of design or
> conditions, something which is theoretically possible, but quite
> unlikely, up to RSP and quite plainly not the case after RSP."
>
> Seems to me to be consistent with what Aitor Coteron said early
> in our discussions when he sent his video :
>
> "The line goes where the rod tip goes... only when the whole
> length of the line is aligned with the trajectory of the rod tip."
>
> Gordy
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
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