The way things were argued earlier in this thread a rotating system needs a centre of rotation - not a fulcrum. Posts 34 and 35 make that explicit.
Yes they are the same thing if you look at the "fulcrum" as being related to connotation implied in the second part of this definition;
QUOTE
Fulcrum - the point or support upon which a lever pivots. The point around which a lever rotates.
and not the first since it is just a point in space and could not "support" anything.
I would get rid of the words "lever" and "pivots" as well, and say the instant center of rotation is the point in space about which all points on a rigid body are rotating (not pivoting) about at one instant of time.
Fairly comprehensive statement of the case? Leaving aside the issue that the 'rigid body' in our case is sort of bendy I guess the grip or butt section is 'rigid enough'.
Well I don't know Magnus, I always thought that a lever required a fulcrum to operate and that a rod was a flexible lever. I'm in the dark here until someone explains why the rod is now not a flexible lever... and even then I may be in the dark for some time!
Looking forward to someone switching on the light.
I'm in the dark here until someone explains why the rod is now not a flexible lever.
Paul,
We may be starting to count the angels on the head of a "fulcrum", but if we look at a lever as magnifying the distance the tip end of the rod moves relative to a given rotation of its butt, the rod is still acting as a flexible lever.
What it is not doing is operating as a classically-defined first or third class lever that involves the use of a support fulcrum located somewhere along its length. To operate as a first or third class lever would require that a force is applied some distance from the fulcrum point to move a load that is at a different distance from that support point. Thus the classical definition of a lever includes a "fulcrum" in its implementation, and would require the rod to rotate about some point that was located somewhere on the rod.
In our case the rotation center could be located at a single rotating joint (the shoulder for example) if the angle of the elbow and the wrist were held rigid. In that case you can see the end of the rod might move 10 cm or more while the shoulder only rotated 2 degrees. Thus the rod is still acting as a lever to magnify the motion of the shoulder, but there is certainly no "fulcrum" involved to get that magnification.
In the more general case where a combination of joint movements are causing the rod to translate as well as rotate, then the apparent rotation center can be anywhere in space. In fact if the motion involved pure translation there would be no true instant center of rotation since by definition it is not rotating. As a result the computed value you would get for the ICR in that pure translation case would be at infinity.
In short unless you fix a pivot point on the rod and then push or pull the butt of the rod about that rotation point there is no true fulcrum. Thus trying to describe a casting style as using a rotation point (or fulcrum) located on the rod is very misleading. Even in single handed casting the ICR is rarely located at the wrist.
In short we use the rod to magnify rotation motions of different joints in the body but we do so without requiring the use of a supporting fulcrum to achieve it.
Since some people do not see the distinction in the thread it bears repeating that:
As repeatedly stated by Alejandro, Grunde, and me, it is because there is no "supporting fulcrum" (fixed or moveable) in a two handed cast.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
That classical definition of a "lever" would require the rod to rotate about some point that was located somewhere on the rod.
So, evidently, our rods are not flexible levers - who knew
Good lord! All the textbooks that give a fishing rod as an example of a type of lever now need to be re-written.
Odd thing about this is I understood levers to be one of the 'simple' machines. So all complex machines used combinations of the simple guys. A sort of atomistic approach to things. Wrong again
Good lord! All the textbooks that give a fishing rod as an example of a type of lever now need to be re-written.
Magnus,
Re-read this again, and you may not be so shocked and taken aback::
We may be starting to count the angels on the head of a "fulcrum", but if we look at a lever as magnifying the distance the tip end of the rod moves relative to a given rotation of its butt, the rod is still acting as a flexible lever.
If you do not agree with that view, and purport that of course a lever requires a "fulcrum", then can you point out for me where the "fulcrum" is in the casting robot, or where it might be in the equivalent situation where someone is casting with a stiff wrist and just moving the rod by rotating their elbow?
Can't a lever be considered as a tool to magnify the distance the end of the rod moves for a small rotation at is butt?
I am not much for counting angels as you seem to be. A rod can be certainly be rotated without the use of fulcrum. so just widen your thinking a bit as to what a "lever" can be.
If someone says that a fulcrum is required somewhere on the rod to get it to rotate, then their books should be re-written.
A "fulcrum" is not required to rotate the rod as any shoulder and elbow dominate tournament caster knows.
Just ignore the reference to first class or second class levers in your casting book. If they were looking at casting from that narrow perspective of what a lever is, then I would look elsewhere for my physics of casting information, and just pay attention the other aspects of their instruction.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
I think I've got it - thanks Gordy. What I don't understand is how you end up therefore with a fixed point fulcrum when it moves throughout the cast. I know that you've undoubtedly explained it!
As far as I'm concerned the classical definition of a lever seems to require a fulcrum. Can't find a definition of lever that doesn't have one.
As for the casting robot, the fulcrum is within the hub - as you know the forces acting at the axle cause the movement and the position of the centre of the axle doesn't change.
I may well be waving hands or counting angels - do I care? You seem to have a taste for these sort of cliched slights - far as I'm concerned it's water off a duck's back
Since this debate/discussion started may I ask a question?
Have you spent any time casting a DH rod and looking to find out where Im coming from or are you dismissing me based on stuff written in physics books? having said that Ive yet to see a book which says a lever can operate without a fulcrum?
I have tried my best to look at things from your angle, as a man with clearly more technical experience and as yet nothing you have said switches any lights on for me.
I wonder if you spent some time casting with an open mind there may be a flicker or two for you?
Levers are classified by the relative positions of the fulcrum and the input and output forces. It is common to call the input force the effort and the output force the load or the resistance. This allows the identification of three classes of levers by the relative locations of the fulcrum, the resistance and the effort.
Class 1: The effort is applied on one side of the fulcrum and the resistance on the other side, for example, a crowbar or a pair of scissors or a seesaw.
Class 2: The effort is applied on one side of the resistance and the fulcrum is located on the other side, for example, a wheelbarrow or a nutcracker.
Class 3: The resistance is on one side of the effort and the fulcrum is located on the other side, for example, a pair of tweezers or the human mandible.
These cases are described by the mnemonic "fre 123" where the fulcrum is in the middle for the 1st class lever, the resistance is in the middle for the 2nd class lever, and the effort is in the middle for the 3rd class lever.
I have no doubt whatsoever that a fly rod either SH or DH is a lever and there aren't any more lever classes than 3 so surely its simple enough to identify which rod type and casting style falls into each?
For a SH rod I could see the fulcrum being in the shoulder, elbow and wrist at different stages in the cast and always acting as a 3rd class lever.
With a DH rod I think the lever type can differ depending on the direction from which the force to operate it is applied.
Does it really have to be any more complicated than this? Unless of course we include our entire body as part of the lever and our feet are the fulcrum in a 3rd class lever arrangement
ps The clever stuff at the top is not my thinking, it came from Wikipedia and is backed by significant other references.
What I don't understand is how you end up therefore with a fixed point fulcrum when it moves throughout the cast. I know that you've undoubtedly explained it!
Paul,
The instantaneous center of rotation is not a fixed point fulcrum. I don't think a fixed point of support exists in casting other than the stuff that keeps our joints together.
The ICR is not a point of support or a fulcrum. It is just a point in space that all the points on a rigid body are rotating around at one instant of time.
Try reading the Wikipedia description again to see how it works. They can explain it much better than I have.
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
If you can't look at the lever concept with a more open mind as to also being a simple machine that can magnify small rotations at one end to effect large tip travel distances at the other then for you the rod is not operating as a flexible lever. For me (and I think most others) it is.
If you require a fulcrum for it to be considered a flexible lever and thus want to think of the rod as part of a simple machine that you could use to to lift a heavy object (where a fulcrum would be involved and meet your lever requirement) that is fine with me as well.
As for the casting robot, the fulcrum is within the hub - as you know the forces acting at the axle cause the movement and the position of the centre of the axle doesn't change.
I think it requires a big stretch of imagination or a very distorted use of the accepted meaning of technical words to call a rotating bearing (a machine part in which another part (as a journal or pin) turns or slides) and turn it into a fulcrum (the fixed support about which a lever turns).
I think you are well aware a bearing is not a fulcrum.
As far as I'm concerned the classical definition of a lever seems to require a fulcrum. Can't find a definition of lever that doesn't have one.
I think all references to a classical lever also make use of two different lever arms whose position relative to the fulcrum vary depending on the class of the lever. Where do you see the second lever arm about the mythical fulcrum in the casting robot?
I may well be waving hands or counting angels - do I care?
I must admit your harping on my use of "idealized examples" or asking what I assumed to be back handed questions (i.e. ones your already know the answer to) do get to me.
I am never sure why something I said or a particular point of view I have expressed seems to irritate you; but apparently it does. It may be a cliched "water off a duck's back" to you, but it is not to me.
I try to be patient and informative with the data I bring to these discussions, and if you want to dispute some of it, great. I would appreciate if you would counter what I say with some data of your own, not some back handed question or snide remark.
I am not a wordsmith with an English degree, but a common engineer who has a very limited way of expressing dynamic principles to lay people. That limited vocabulary works fine with those who have a technical background, but it seems to offend people that don't. It is a bit of a puzzle to me, but a wiser person offered:
What surprises me is that you can still be surprised!
This is how it has been working for a long time. Instead of trying to put their knowledge in common with others to advance in the general understanding of this fascinating subject, they just try to appear as smarter than the rest without any other goal.
I don't think that is the case with you, but I think we both should try to abide by the lofty goal noted in the first part of that statement. Let's try to learn from each other, and leave the harping to closed-minded people who seem to be unable to change their mind about any of their long-held views of casting
Gordy
"Flyfishing: 200 years of tradition unencumbered by progress." Ralph Cutter
sms wrote:1. Effort is work, right? work = force x distance.
2. Since both hands exert roughly the same force on the rod, the work done is in relation of the movement of the hands.
like you need to put in effort.
1. Agreed
2. I am yet to be convinced that both hands use the same force and I have proven that one hand moves over a significantly greater distance.
Ok, let's assume a 15ft rod. We are casting, the line is straight back in horizontal position and we are doing the forward cast, the rod is in vertical position. Thus the rod butt and line are perpendicular. Let's say the rod has bent so that it's effective lenght is 4m (about 13ft). Bottom hand at the very butt and top hand 0,5m above the bottom hand. We are applying force of 5N (Newton) to the line. The bottom hand is then pulling with force of 35N and top hand 40N. The closer the hands are each other compared to rod length, the bigger the difference, but it is not very significant.
I'm here just for the chicks.
President of The Village Idiots of Vantaa Rapids
President of The Casting Federation of Finland
If we consider the lever as classical one, then we need to have fulcrum and we have the three types of levers. And as fulcrum is not doing any work, it is stationary. So, we either need to throw the classical lever out the window or set our world around in DH casting in top hand (setting that a fulcrum) or in bottom hand (setting that as fulcrum) - for any cast done with any movements. Not very helpful. It's like two guys walking on the street and one says he is walking 107000 km/h (the velocity of Earth around the Sun) and the other one says he is walking about 900000 km/h (the velocity of the Sun around the center of Milky Way). And the truth is, in regards where they are going, and thus matters, they are moving like sloths, 1km/h.
How about SH rod then? Well, top fulcrum would be thumb (let's assume thumb on top grip) and bottom would be pinky finger on FC. On BC they would be different....
So, in my opinion, the traditional lever definition for rod needs to go out the window. Otherwise we are moving quite fast standing still.
I'm here just for the chicks.
President of The Village Idiots of Vantaa Rapids
President of The Casting Federation of Finland
please let's have a look at a sketch, I fingerpainted this morning with a new prog on my ipad.
Please excuse my inability to paint better.
In the upper left we see a planet and 2 moons rotating around the planets center in some distance.
Let's have a look at the different pics:
Pic 1 (upper right)
Configuration:
Planet is static.
Moons on the spheres around the planet.
The measurement:
The perpendicular of the velocityvectors from the moons are pointing to the middle of the planet.
The Planet does not have a movement at all. No movement, no velocitiyvector, no perpendicular.
Result: The I.C. is located in the middle of the planet.
-------------------------------------------------
Pic 2 (middle)
Configuration:
The same as 1, but the Planet translates from right to left.
Moons follow on the spheres around the planet, like in Pic 1 (no change)
The measurement:
The velocityvectors of the moons are now seen as circularsegment movements.
Their perpendiculars meet somewhere on the translationaxis of the planet.
The Planet translates, therefore no rotation = no rotationaxis.
The perpendicular of the velocitiyvector of the planet does not clearly unite with the moons perpendiculars,
because he possibly can be anywhere on the translationaxis of the planet.
= The movement of this 3 objects do not have a I.C.
Result: No I.C. (or as MatLab measures = I.C. in infinity)
-------------------------------------------------
B]Pic 3 (bottom)[/B]
Configuration:
The same as 1, but Planet moves on a circularsegment from right up to left down
Moons follow on the spheres around the planet, like in Pic 1 (no change)
The measurement:
The velocityvectors of the planet and the moons are now seen as circularsegment movements.
All of the perpendiculars of this 3 objects meet somewhere in space.
Result: I.C. somewhere in space, but not in the planetmiddle.
How I see it is you have ridiculed use of the term fulcrum because it fails to meet a fairly strict interpretation of the classical definition of a lever. 'Poor foolish laymen - how dare they misuse a term and use a loose interpretation of a concept.'
However you allow yourself to bend that classic definition as needed. 'Nope that's not mucking around with the concept that's just being 'open minded'.'
Can you see a double-standard at work in there Gordy?
I try to be patient and informative with the data I bring to these discussions, and if you want to dispute some of it, great. I would appreciate if you would counter what I say with some data of your own, not some back handed question or snide remark.
This ain't the technical forum Gordy.
In a quest for data, on a scale of one to ten, how patronising do you think an opening statement like "I try to be patient and informative..." sounds?
If you can't look at the lever concept with a more open mind as to also being a simple machine that can magnify small rotations at one end to effect large tip travel distances at the other then for you the rod is not operating as a flexible lever.
I guess the grip or butt section is 'rigid enough'.
