Translation/Rotation.... PHYSICS DETAILS

From Walter Simberski. (Note his attachment You may need to scroll down to see his new diagram ):-

Bruce's diagrams are carefully drawn and are 100% correct but I think it might be worth pointing

out again that he has reduced the examples to rod motion only. As such, they are conceptual

If we get into a mind set that says if the butt end of the rod moves through space we must have

If we hold the wrist rigid and rotate the lower arm and rod combination about the elbow we will get

something that looks very similar to Bruce's drawing depicting a mixture of translation and rotation,

i.e. the rod will rotate and the butt of the rod will move through space, but the motion will be rotation only.

I've taken the liberty of attaching a modified version of Bruce's spreadsheet showing what I hope

are some clarifications regarding rotation and a mixture of translation and rotation. Bruce

was very careful to show that the axis of rotation (the point that the rod is rotating around) is

the very butt end of the rod. As you can see there will be a subtle difference when the axis

of rotation is moved to the elbow and we take away translation - the butt of the rod will move

in a circular path, not a straight path - but the outside observer could think they are seeing a

I came across a fairly good discussion of translation vs rotation at the following web site:

I'm curious - I haven't heard a response from you regarding my question of whether it is

possible to pick up 30 feet of fly line plus leader using translation only. Did you get my email?

I could make it more of a challenge and ask whether it is possible to pick up 50 feet plus

Again - I fully agree translation and rotation are not subjects for most students. I do find them

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There is no disputing your conclusions. This is one reason I looked at rotation as almost always admixed with translation and vice-versa....

However, I didn't want to get into the intricacies of physics which you understand in much greater depth than I .....

In particular, I didn't want to confuse the issue with our Group members, the vast majority of whom are not scientists.

Just as you have exaggerated the axis of rotation in your diagram by placing the, "handle" of the, "rod" half way up the shaft, Bruce and I have exaggerated in the opposite direction .... that of utter simplicity ..... to make a point , realizing that from a strictly scientific view, there are some inaccuracies.

In order to simplify things to make a single issue as clear as possible my discussions and Bruce's along with his depictions didn't consider rod bend, either.

I think the biggest problem we encounter in trying to study fly casting is that it is an inextricable kaleidescopic compendium of events involving flexible materials being manipulated by different means and by different human beings. The variables are almost beyond understanding. To teach it, we have had to reduce it to easily understood segments ...... and then try to put it all together so our students can actually cast.

In studying the material in the link which you provide, I found some interesting things about TORQUE which I hadn't known. One was the apparent attempt to depict torque as a straight line vector ! The author apparently hadn't solved that problem in his own mind, and passed it off as he continued with other discourse.

Ally has asked questions of the Group on TORQUE as it applies to fly rods and casting.

As we discuss this new topic, I'd like to keep it at a level understandable to all and not get into the detailed physics unless we are to be proven dead wrong .........................

Long answer: I did get your message. Before answering, however, I went out and tried to do this on grass and on water.

Firstly: I couldn't convince myself that my trials were with pure translation. Second: I could pick up from grass, but not water to the extent that my fly/leader did leave the ground.... however, no true cast resulted.