Necessary terms

[Paul Arden]

Some of us are on the moon, Tony.

[flybye]

Hi Paul,
That must be where the Masters hang out
TK

[Paul Arden]

:laugh: Probably!

[Hal Jordan]

" As we are not on the moon the difference between mass and weight is surely semantic rather than physical "

Again - maybe I'm being too picky, and I apologize if that's the case, but think of mass as the factor that determines how an object moves in response to a net force in any direction. Weight is more about how things fall. When we model how things move we often ignore gravity in the initial stages and concentrate on the other forces that interest us. Otherwise I'm cool with mass and weight being interchangeable.

[Hal Jordan]

Great list, so if we collected all these terms up do you think it would be possible to explain what they are used for, the relationships between them and how they apply to casting mechanics. ? No Data, no graphs, just words and, maybe...pictures.

Again, imo the two most important things to know and understand are:

number one:

F = ma

To really understand that you need to understand Newton's laws and understand that F and a are vector quantities and what that means. You also have to understand the concept of center of mass when talking about fly line. We can get in to all sorts of discussions about rotation and have charts and videos galore but ultimately we are concerned about getting the fly to the target and the best way to do that is to move the rod tip in a near straight line so the rotation stuff is more than most people need to know. You should also understand that part of the F includes gravity and the most important thing to understand about gravity is that things fall down.

The second most important concept imo is that the greater the force applied to the rod the more it bends (Hooke's law sort of) but then I've yet to see a rod that bends less when more force is applied.

After that it's good to know why engineers say you can't push a rope.

If you want to get real extreme you can talk about terminal velocity and why a loop can travel much faster than line falls.

The rest of the stuff beyond that is interesting to a few geek types but I don't know how much more most instructors really need to know or want to know.

I agree with what you are saying. There is a need for this sort of thing but imo my first post was already well beyond what an instructor needs to know. I've also said before that SL should have a "not quite so technical technical forum" where physics/mechanics can be discussed without being inundated by graphs and reams of data. Pictures are good (with the exception of my butt cast picture from a previous thread). Models can be really good as long as one understands the limits of the particular model - Grunde's car/brick/spring model for example was incredible stuff and we all learned a lot from it (well at least I did).

Maybe the first challenge, which I think you are suggesting, is paring down to the essentials.

Anyway - great discussion topic! Hope to see more of this type of thing.

To answer your question that I quoted - yes I think it would be possible. You have some incredibly bright people here and they are motivated. If they can't do ith then I don't think anyone can.

I'm going back into hibernation now...

[gordonjudd]

Great list, so if we collected all these terms up do you think it would be possible to explain what they are used for, the relationships between them and how they apply to casting mechanics. ? No Data, no graphs, just words and, maybe...pictures.

Mark,
I don't think that the details of dynamic principles can be fully communicated just a glossary of technical terms or pictures. Unfortunately, the physics of casting is a whole lot more complicated than F=ma.

The more I get into the physics of casting the more complicated it becomes. A reading of Goriley's whip wave paper or Dr. Gatti-Bono's thesis will make you wish you had a PhD in mechanical engineering so you could grasp the details of what is going on. The threads in this forum, are very elementary compared to concepts that are of interest to academics that are digging into the real details of what is going on with the physics of casting.

I have only had one person who expressed an interest in the physics of casting in my involvement with the beginning casting classes at the Long Beach Casting Club (and he was an engineer) so I don't think this is a subject that has much interest for students.

I do think it should have some relevance to instructors however, as teaching concepts based on bad physics is not the best way to advance the sport. The top hand fulcrum concept in two handed casting is a case in point, but I have found you will not be able to convince people that believe in it, that such a fixed rotating point does not exist.

In terms of basics I think it is important to understand where line speed and/or rod tip speed comes from.

For that you need to understand the basic work energy principles involved with applying force over a distance to the line and torque applied over angle for the rod. However, it seems these basic energy relationships go over the heads of most non-technical people as I rarely see these very fundamental ideas making anyone's list of important "technical concepts."

Merlin and Grunde's model of casting using a simple (which is not so simple in reality) forced harmonic oscillator should also be something that instructors with an interest in casting mechanics should understand.

Gordy

[Stoatstail50]

That's very sad Gordy.

Here at work we have just trained and now independently qualified six people as lifting engineers. They knew knothing about it when they started . Good teachers were able to explain complex concepts in a simple and digestible way. Why can't we do that for casting....? Is it too special ?

Grundes spring brick model was not intended to be used as a model for a cast. I remember the first time he posted it up and I seem to remember he made that quite explicit. I asked him about it in Scotland a couple of years ago and its quite clear that it is far from a complete analysis and he never, to my knowledge, claimed that it was.

[Merlin]

OK, models are far from perfection but they help to understand. They need to be challenged by experience.

I agree that there is the necessity not to use any equation or formula since most people do not know about the basics of physics. Graphics are highly recommended to illustrate the words. By the way, I do not think that the word "vector" is palatable for a non scientist.

When an instructor asks a question to a student/candidate, what is his intention? I would like to know the most common questions used to understand that. To which extend do you expect one can understand the physics of the cast? Should the student know about the main drivers? What type of language do you expect from them? This should give you a list of words. Mechanics may be twisted by some words like “speed” instead of “frequency”, “weight” instead of “mass”, you have to get prepared to be tolerant and oversimplify the picture. I do not think there is a place there for stop/ nonstop discussion, rotation vs translation, or linear/non linear springs, etc. in the first place. You could imagine several level for the exam, providing you fully understand them yourself, moving gradually from not too much technical terms to more precise mechanical concepts and definitions.

Many thanks in advance for providing me with a list of most frequently asked questions. I'm trying to write something simple on the physics of casting, and this is really not easy.

Merlin

[Hal Jordan]

Merlin and Grunde's model of casting using a simple (which is not so simple in reality) forced harmonic oscillator should also be something that instructors with an interest in casting mechanics should understand.

The first thing they should understand is why it isn't a complete model for the cast. When they understand that then they can understand where it should and should not be applied.

Electrical engineers have a different view of modelling than mechanical engineers.

[TrevH]

This is great stuff. I was struggling with the concept of KE and whether I needed to worry about it in casting mechanics.

Whilst I can get a value for it, I'm not sure what to do with that value. At least, not in the same way a momentum, for example.

I am in the early days of trying to work out an irreducable set of concepts that I need to know to explain flycasting and I was hoping to cross KE off the list. The alternative is I need to understand it (I mean "need" in the loose sense of the word, you understand :-) )

I was liking Mark's list :-)

Hal's list horrifies me :O But it fascinates me all the same so it's all good stuff.

Sorry, I've not contributed a great deal, I've still got a lot of research to do, but at least you know there are interested people out there.

[Merlin]

I believe the SHO is a good starting point for understanding the physics of a cast. Not perfect for the specialists for sure, but do you need more for an instructor?

As simple or complex as it is, depending on your knowledge, it is a very interesting tool. You can guess that sophisticated software with a more realistic approach is better, but do you need to know about that to cast properly?

Merlin

[Hal Jordan]

Merlin - the sho explains the interaction between a spring, a weight (basically a point mass) attached to one end of the spring, and something that applies force to the other end of the spring. If you find that to be a complete model for the cast, or a good starting point for the mechanics of the cast, then fill your boots.

Do I think sophisticated software makes for better analysis? Absolutely not.

Personally, I think a complete understanding of concepts like "equal and opposite forces" to be far more useful.

[Paul Arden]

I don't think it's about the rod. I think it's about the loop. Tension. Mass. Velocity. Momentum. Explain basic loop physics - which are fairly incredible by the way - and you've pretty much explained 90% of the cast.

Sure the rod bends, but it doesn't have to. In fact we don't even need one. It's all about the loop. The tension is a result of momentum change at the front of the loop, and it's Tension that pulls the fly leg. Simple but very enlightening concept.

Cheers, Paul

[Hal Jordan]

I don't think it's about the rod. I think it's about the loop.

I think I missed that part about loops in the sho model.

You may have identified even more than 90%. Energizing the line (i.e. getting it up to a desired speed) and forming a loop are what counts. I've heard of people who can cast upwards of 80 feet hand casting and more than that using a chopstick with a tip guide. The rod may provide a mechanical advantage but, as you say, we can cast without it.

[Magnus]

The rod may provide a mechanical advantage but, as you say, we can cast without it.

Hi Walter

I thought using a rod meant the force at the rod tip was smaller than the force applied at the butt - so the Mechanical Advantage (which is about input and output forces?) is poor. However the Velocity Ratio is high - made higher by the springy nature of the rod. So the velocity of our casting movements is magnified.

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=ENG20804
(Incidentally these fools have the lower hand static - like it's a fulcrum )

Incidentally if one of you physics guys would care to clear it up - I've found two completely contradictory explanations of VR - basically one is the input over the output - the other is the output over the input - can't both be right.