I've been giving this some thought. With a longer rod (with the same relative stiffness and action) you don't get as much actual movement at the rod butt in terms of distance, but you're exposed to a much greater amount of power or force. So we're not talking movement or amplitude, but force.

A fish bite is more often a simple stopping of the lure or bait, or a tug, than any sort of distance movement or vibration. So... I may be all wet and should certainly think about this some more, but I am currently thinking the force that occurs against the fisherman at the rod butt may be a major, if not the major factor in rod sensitivity. And if so, then a longer rod is a more sensitive rod.

I'm not about to write off the other factors I've harped on over the years such as mass density or stiffness to weight, but rod length is an aspect that I think probably plays a much greater role than I had ever considered. Thanks to Jim for bringing it up.

I may change my mind by tomorrow, but I'm going to sleep on it and see how it looks in the morning.

....................

Tom,
If I understand what you are saying I don't think that I agree. If the rod is twice as long it has twice the mechanical advantage so only half the force is necessary at the tip but the tip must move twice as far to get the same amount of movement at the butt as with a rod that is half as long. In both cases the amount of work done is the same, and the force at the butt is the same.
As I think more about your example of the rod acting as a lever lever I am bothered more about the type of lever it is and what happens at the fulcrum. There is no movement at the fulcrum of a simple lever. If the fisherman's hand is the fulcrum then he should feel nothing regardless of how long the lever, or in this case, the rod is. I need to think about this more. Obviously the fisherman's hand cannot be the fulcrum of a simple lever.

Tom,
I have thought about this lever problem a little and think that I have it sorted out, at least to my satisfaction. I have forgotten which is a type 1, 2 or 3 lever but when we are casting the fulcrum of the lever is usually our hand but in order to feel a fish's bite the type of lever has to change and the fulcrum basically is at the butt of the rod not at our hand or at least the fulcrum is behind our hand.
Now back to your question. The movement and the force at our hand will be the same regardless of the length of the rod but for that to be the case the tip of a rod twice as long has to move twice as far. The force required to move it will be half as much but it will have to move twice the distance. But if the tip of the rod moves the same distance for the longer and the shorter rod there will be twice as much movement at our hand with the shorter rod. And if the mass of the two rods is the same and the stiffness of the two rods is the same and all that changes is the length then we are back to the conservation of energy. If there is no energy lost in deflecting the rods, they are perfectly stiff, then the movement and the force at the fisherman's hand will be the same regardless of length. In a practical sense though the rods will not be perfectly stiff and the longer rod will have higher mass, and tend to be less stiff so the shorter rod will be more sensitive. Did all of that make sense?

Well the thread has made it to the second page - Tom is hopefully sleeping (dreams or nightmares), Emory is thinking, a few are plotting and the rest of us are happily lollygagging along waiting for morning. After all the scientific minds have identified all the possible variables involved. I find it almost impossible to believe that the most important one of all has been ommited totally from the discussions. No matter how you feel about the discussion remember SIZE MATTERS and should be always be included.

Gon Fishn

Emory,

From the fisherman's standpoint the rod is a 3rd order lever. To the fish, it is a 2nd order lever.

Again, forget about movement in terms of the distance the rod moves. That's not important. What I think is important, is the force applied to the fisherman by the lure stopping, or being hit and pulled on. And with the fish operating a 2nd order lever, a longer rod will allow the fish to hit the angler with more force for any motion on the part of the fish.

It would be a simple matter to mathematically equate the force applied to the fisherman at his point of effort for any given input at the rod tip. And even a few inches in additional length will make noticeable difference. The load times its distance from the fulcrum is equal to the effort times its distance from the fulcrum.

But beyond that, I'm betting that any stop of the lure or tug on the end of the line, is going to be felt much more strongly by the fisherman with a longer rod than with a shorter rod. Outside of amplitude, movement, etc., there is still force to consider. And for any "tug" on the line at the fish's end, the force against the fisherman is going to be greater with a longer rod than with a shorter one. Even if we're only talking about a tap which takes but an instant.

Granted, there is going to be some trade off in terms of the longer rod adding some weight to the equation, but I'm not sure if the modern type rods we deal with would see the reduction in sensitivity due to added weight not being more than offset by the increase in force against the fisherman by that same length. I have to think on this some more.

..............

Ken Finch wrote: "I know enough about the subject at hand to know when somebody is just trotting out textbook information, without actually knowing if it's pertinent or not. There is a poser in the crowd, probably hard at work digging up some additional non-pertinent mumbo jumbo to throw at us here!" -Ken Finch.
Re: Rod Sensitivity... March 20, 2007 ... 03:51PM

Dear Mr. Ken Finch - The fact that the "pertinent information" is our chief interest in rod-building in no ways undermines the fact that a complicated set of mechanics and mathematics applies to and can readily be used to explain & discuss various characteristics of a rod blank, such as "sensitivity".

It just so happens that for the purposes of this discussion on sensitivity, the pertinent information involves those equations, those mechanics (statics, dynamics, material science, strength & materials, wave functions, etc.) and that level of mathematics (at least algebra). This is a "LIKE IT OR NOT" situation. I seriously doubt that Mark Gibson (Polymer Chemist & Material Scientist) or Emory Harry (Electrical Engineer) or Mike Naylor are interested in impressing us with their knowledge. Sharing their knowledge -yes! Establishing their credentials -maybe. But "showing off?" -I'm sure they have better things to do with their time, if that were the main motivation. IMO, I am fully convinced that they strive to "Keep It Simple, Sherlock" around the RBO Forum, … because their interest is to ELUCIDATE the facts, not ALIENATE the RBO and RMM Reader; and to NOT propagate anecdotal mis-conceptions or rod-building "myths" in the process.

Mr. Finch, your comments here are based on well-established principles of rod-building, as are your carefully articulated observations. You said in plain English much of what Mark Gibson & Emory Harry said in a terminology that is somewhat different than yours.

The dilemma enters when we strive to determine the RELATIVE IMPORTANCE of the many variables involved in rod blank "Sensitivity". And frankly, that is VIRTUALLY IMPOSSIBLE to do without equations that show the inter-dependence of the variables, and some range of numerical values for those variables. (Mike Naylor implied this, too.) To think otherwise is to involve yourself in a discussion which is not capable of arriving at definitive conclusions because the entire system is not defined in the first place!

I, too, "know what I am talking about" as a fisherman, and a rod-builder who is also interested in the physics of rod blanks & rod-building. And I have taken (and nearly failed!) enough engineering classes to know that until you can put an equation down on paper, and plug-in some numbers, and generate values which allow you to factually analyze & discuss a system (the rod blank), then all the hand-waving in the world will not change the PHYSICS of the universe and its pertinence to rod-building. Period.

I don't know what the grandmothers around here would say, but I know what Lord Kelvin said about such matters: "If you cannot measure it, if you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind." (Ouch!) ….. He is one of the fellows responsible for determining the value of temperature called "Absolute Zero" in chemistry and thermodynamics ( -273.15 C). Space travel may have been impossible without that knowledge. … Just as deeper understandings of rod blank performance are limited by one's knowledge of rod-blank mechanics …

As rod-building "scientists", rod-building artisans, and fishermen alike, let's keep the discussion open, … and our minds & hearts as well. …
Thanks for your consideration. … -Cliff Hall, FL-USA.

P.S. - I know that I for one find it next to impossible to sort out the relationships between so many related variables without a set of equations and a key legend for the definitions of all the variables. I have read hundreds of passages of presentations, derivations & proofs for the various laws of physics, math & chemistry, and worked thru (solved) ten times that number of problems in each of them in my 5+ years of college-level education and 14+ years of professional career. I have yet to encounter a better system of discussion than a rigorous, formal presentation that involves a description of the problem, definitions of the variables, sets of equations, and verbal development of the subject, leading the Reader to the next premise, and finally concluding with a discussion, summary, & conclusions. … Such a format is typical of scientific treatises in many disciplines, because it has proven itself to be superior to colloquial forms, until all parties involved are "on the same page." Without such a format, the conventions are ambiguous and a consensus of opinion is very improbable. … It is clear from the several discussions that have transpired over rod blank "sensitivity" on this RBO Forum in the last 2 months, that we are not all on the same page yet, nor is everyone really understanding each other, or the mechanics (physics) of rod blanks. -Cliff Hall