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Physics of the Fly Rod by Daniel le Breton

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How does a fly rod work? It is amazing machinery which seems to escape common understanding, and there are good reasons why. Fly rods have been developed over more than 100 years, and space age materials and computing science have contributed to improve their design. Impressive modeling of a cast has been performed but the complexity of this approach does not help us understand the underlying basics quickly.

Viewed from the bridge, a fly rod is both a lever and a spring, sometimes we use it as a pure spring (bow and arrow casting), sometimes as a nearly pure lever (leader casting only), and most of the time we take benefit from both functions. The lever allows us to generate a high speed using a simple rotation, but what about the spring?

Casting instructors are familiar with the casting essential of SLP, or straight line path of the rod tip, but the path of the rod tip is only part of casting efficiency. Mechanically speaking, it is most efficient to move an object along a trajectory by pulling along that trajectory. This is why to cast a line; it is desirable to generate speed on the flattest possible trajectory and to align the line with the path of the rod tip, aiming at the smallest possible loop. The flexibility of the spring allows us to achieve that goal with more or less success, and we can say that this property of the spring is complementary to the advantage of the lever.

But there is more than that coming from the spring function. There are hidden properties that I shall try to show you, and you will realize, I hope, that there is some kind of magic in a fly rod.

Let’s start by the beginning: the spring is also a speed amplifier (the lever also has this property, but it works differently). Casting a line with a fly rod is similar to launching a marble by pushing it with a spring along a flat table. Depending on the way we push on the spring (along a straight line), the speed of the marble can be increased up to 40% by comparison to the maximum speed of the push. It can also have no amplifying effect if you do not push properly on the spring: it is a question of timing. On top of that, it is a question of spring and marble characteristics, which goes along with the push. So let’s concentrate on that “spring & marble” system, which is our “rod & line”.

The single characteristic which is important for the speed amplification is the frequency of oscillation of our system. It depends on the natural frequency of the spring and on the mass of the marble. The heavier that mass, the slower our system becomes. So we have to adapt our timing, and this is why DH rods are different from SH rods in terms of frequency (which we usually call speed). DH rods are slower to adapt the tackle to our physical capabilities.

The frequency of the tackle drives its response to our input, and there is nothing straightforward here since we are under what we call “transient conditions”: the spring oscillates just one time up to the launch of the marble. It is rather tolerant. If your timing is not perfect (acceleration followed by deceleration to a stop), then the speed amplification is still significant. You must cast a noodle (extremely slow rod) or a broomstick (extremely stiff or fast rod) to lose speed.

The speed of the marble is also determined by the distance covered during the push (the casting arc): the greater that distance, the greater the marble speed.

The spring function is able to explain the importance of adapting our casting arc to our objective. Most of the time we use a more or less constant timing (longer for a DH rod), and thanks to rod designers the frequency of the tackle we are using is matched to our physical capabilities. This simple approach of spring function allows defining a line scale if you need one. Have we found the basics here (tip trajectory, casting arc, timing)? I think we can say yes, but there is more than that.

Fly rods are hard springs (non linear), which means that they resist more and more to bending as we increase the load or bend: you begin at the tip but you face the butt after, and it is really stiff. This increase in stiffness occurs as you lengthen the line, and this allows us to cast a longer line, because it maintains the frequency of the rod & line system on the high side. Consequently the line speed is also maintained on the high side, which is needed if we want to cast for distance. This is not a small effect; you may get something like 40% again by comparison to a rod having little hardening of its spring, and this comes on top of the speed amplification due to the basic spring effect that we described before. So if you look for distance you will have to choose a “hard” rod, but this may not be useful if you fish at short distance a small stream. It is worth knowing some basic rules: short rods are more “non linear” that long rods. A steeper taper has a non linear effect but it is difficult (it depends on the material) to have a long non linear rod and a short linear one.

If you fish at short distance you may wish to benefit from another strange aspect of the lever. This aspect is due to the spring somewhere, since it is linked to the fact that the tip and the butt have very different speeds during the cast (at the same time). The swing weight of a fly rod (its inertia for a mechanic) is relevant to the difficulty (resistance) to rotate that rod. During the cast the rod deflects and its swing weight diminishes during the acceleration of the butt, which helps reduce the effort for the caster, and it increases again as the rod is decelerated and the rod returns to straight position, which contributes to that deceleration. Swing weight variations are limited most of the time, mostly less than 10% (if the distance between tip top and butt end is reduced by 10%, the swing weight is reduced by 5%; this is just a rule of the thumb). This is why “slow butt action” rods are more comfortable to cast than “stiff fast action” ones, but this is a general statement, not a universal law.

Swing weight seems to be a single number but in fact we can consider that it is made of three components that all have a role to play during the cast. One is linked to the tip and is a major parameter of its natural frequency. The second one is linked to the butt and is important for casting comfort, and the third one is an in between parameter linked to both tip and butt, and it is responsible for the (magic) effect I am going to describe now.

This intermediate component of the swing weight manages the kinetic energy between tip and butt; it tends to counteract the influence of these parts of the rod to our advantage. Let’s describe some phenomenon coming from its influence. As we start casting forward, the tip begins moving backwards for a short while. This is not to be confused with the potential effect of a higher vibration mode (the second one, with a node in the tip), we are accelerating progressively here, and we do not use sharp wrist acceleration. Later in the cast, as we decelerate the butt, the resulting effect is a boost of tip speed, something like 30% for a short line. You get that on top of the 40% given by the spring function, but you get little from the non linearity of the spring under such conditions. So if you are casting a short line, you will appreciate the benefit of this phenomenon. It is the designer’s job to provide this faculty into his rod.

Casting at intermediate distance benefits from both the non-linearity effect and swing weight transfer effect. All in all you may get an additional 30% there too, and that’s good news. If one could make a rod with maximum transfer effect and high non linearity that would be a good one (in fact there are already some on the market).

And this is not yet the end of the story. The intermediate component of the swing weight, by providing more kinetic energy in the tip, takes it from the butt, so it helps to decelerate the butt of the rod just when we need it. At some stage (line length), this deceleration phenomenon is amplified by the effect of the mass of the line being cast. This deceleration effect could take place even if we could stop driving the rod (letting it go at the end of acceleration), this is why I call it the self deceleration mechanism. The mass of the line limits the tip speed boost during deceleration, because there is more mass to move for a limited quantity of kinetic energy available, but then there is a transfer in the deceleration of the butt to our advantage. I am convinced that this is key for tuning a line to a rod, but as usual, the various possibilities in casting style can affect that tuning. It can also explain why we think to cast “stop less” a long line. The weight of the line is helping us to decelerate the rod, up to the point that we do not need to make any effort to stop it if that line mass is large enough.

To conclude, a short summary of the lever and spring functions:

  • Lever: amplifies speed by rotation, allows (because it is flexible) a kinetic transfer between tip and butt to the caster’s advantage
  • Spring: basically a speed amplifier which can be reinforced by a hardening stiffness as load increases.

To me it is not possible to separate these functions completely, they are linked together. At the end of the day, the fly rod has visible and (nearly) invisible properties than can be used by a designer to maximize a desired effect. It has been fascinating me for more than 35 years now, and I think it will still be a subject of investigation for understanding its complexity. I did not describe other properties here, a fly rod has several natural frequencies, the three first being the most influential, and it has some consequences on rod behavior too.

Enough for today!

Daniel, 4 Dec 2015

 

 

 

170 cast vs not 170 cast

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[WS] With respect to rod loading we did have some discussion in this group and the consensus was that “loading” is not a great term and that bending and straightening were better terms to describe what happens with the rod during the cast. I think that saying that a loaded rod is a bent rod is still acceptable.

[DlB]A rod bends because it is loaded by forces: e.g. torque from caster, inertial forces (line, rod weight) and drag (air).Both are linked so it is not a question of “acceptability” but of what you are looking at. Bend speaks to all, load speaks to specialists.

[WS] I like that. In the past I’ve talked about load being a mechanical engineering term that actually makes good sense in this context but most people are not mechanical engineers and are not familiar with this term or its use in this context. Bend is a term everyone understands.

The issue is that saying that a rod is loaded creates the impression that the purpose of the casting stroke is to load potential energy into the rod which can then be released at will to throw the line similar to loading a gun or a catapult. This has a few issues. To begin with the energy for the cast comes from the caster. During the casting stroke some energy is stored in the rod and it is recovered when the rod straightens at the end of the casting stroke but this straightening does not increase the amount of energy that the caster puts into the stroke.

[DlB] But to get that stored energy, the caster had to produce it anyway, of course there is no external generation of energy apart from the caster, then it takes various forms: kinetic (rod, line), elastic (bended/loaded rod), losses (air drag).That stored energy goes back mainly into the line at the end (RSP, some is lost through air drag.

[WS] With a gun the energy generated by the bullet is much greater than the amount of force the shooter exerts on the trigger. If we look at European style distance casting there is little or no recovery of the energy that is stored in the rod by bending it.

[DlB] I cannot see a technical reason for that lack of recovery. How would you explain it? Because of the angle between the rod and the line at the end? For me it goes into the line, or should I say into the fly leg and also into the loop for a 170 style.

[WS] I know we’ve had this discussion before and I don’t think we will come to complete agreement on it. Given that force is a vector quantity we need to apply force in the direction that we want an object to move in order to make it accelerate and move in that direction. If we apply force in any other direction than we intend the object to move in then the object will not move in the direction we want it to move but it will move in the direction we apply force. That should be obvious when we are talking about point masses but the line is a long flexible object so we have to consider that even though we may be pulling the line at right angles to the direction (let’s call this the X direction) we want it to go the line will not move as a point mass in the direction we are applying force, the end we are pulling on will move in that direction but the line following this will form a curve resulting in forces in the Y direction along the curve as well. If we look at rod straightening in a non-170 cast, i.e. we stop the rod so that the rod tip straightens in the direction of the cast, it’s easy to see that whatever potential energy there is in the rod is going to contribute to line speed in the direction of the cast. In the 170 cast the rod does not unload or straighten in the direction of the cast. It unloads at nearly a right angle to the direction of the cast. Only a portion of the kinetic energy that is generated as the rod straightens goes into the fly leg, much of it actually goes into the rod leg and results in the large loops we typically see in the 170 cast. I will attach a picture to make this clearer (I hope).

Another issue is that we can’t do much to prevent the rod from straightening once it has reached its maximum bend. We can perhaps delay the straightening by a few hundredths of a second but short of hitting a solid object with the rod it is going to straighten no matter what we do. One of the main benefits of rod bending and straightening is that it contributes to our ability to maintain a straight line path of the rod tip during the casting stroke. Using the term loading doesn’t really describe this.

[DlB] Above the contribution to a longer and straighter tip path, rod bending allows the caster to put a greater part of the energy he produces into the line. This is why the “flexible lever” is better than the “broomstick” for casting.

[WS] Agreed, but this is really the advanced stuff we are talking about now. Briefly, you are talking about how the spring effect allows us to apply more force to the line over the casting stroke than we would be able to with a “broomstick” or a rigid lever.

I’m comfortable with bending or loading, but maybe bending is more practical for instruction since anyone can see it.

Thanks Daniel! This is a very interesting discussion.

[embeddoc url=”http://wildoutfitting.com/testwp4920/wp-content/uploads/2015/09/170vsnot1701.pptx” viewer=”microsoft”]

 

Teaching Scenarios by Dayle Mazzarella

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TEACHING SCENARIOS

Always set the parameters if the scenario is open ended. Always include questions you would ask the student before you start, as well as how you would verify the degree of casting skills.

Review the lesson plan format and adjust your lesson plan to the time you’ll have.

1. An angler calls you and says he/she has been fishing for “ a few years” and is planning a trip to the Bahamas next month. He/she would like a one-hour lesson.

2.  A group of four friends would like to hire you for a two-hour lesson. They are going to rent a cabin on a trout stream in North Carolina for a week. One is “experienced”,       one has “a little experience”, and two are novices.

3. The local YMCA would like for you to run a four-hour clinic for 15 people they have     signed up. You have no idea what level of students will show up or what, if any,     equipment they will have.

4. A husband and wife would like you to teach them “how to fly fish”. They have no     experience, but are willing to spend one hour a week for a month. (The husband is the one who calls,)

5. An older gentleman calls you and would like to become a CI. He has been fishing for     25 years, is now retired, and is looking for a challenge.

6. A Dad calls you and says he’d like you to teach his son to fly fish so he can have a     partner. His son is 12 years old. He would like a two hour lesson.

7. A Boy Scout Troop wants you to “teach the boys to fly fish so they can earn their merit     badge”.

8. The local fly club wants you to run a clinic for its members. They have 27 interested     people. You have four hours on a Saturday morning.

Those are all scenarios I have personally faced! Start at the top and work your way down.  Have fun!

Dayle

FFF/All CI Prep Stuff/TeachingScenarios

Practice with a purpose

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We’ve talked about training rather than straining in order to avoid becoming injured. The next advice in the area of practice is learning to practice with a purpose. The goal is to make the most of your training sessions by continuing to avoid injury and to practice the things you need to practice in order to advance your skills. The things to keep in mind when practicing with a purpose are:

  • Set up a plan and stick to it. If you are going to practice your accuracy casts regularly then don’t let yourself get sidetracked by beginning every lesson with distance casting.
  • Concentrate on the things you need to improve, not the things you are already very good at. Each of us will be different in this respect although virtually everyone will begin with learning to control their loops. Are you able to consistently cast over 85 feet and make it look easy but can’t seem to hit a target? Then you should probably spend most of your time practicing accuracy rather than distance.
  • Start every practice session with some warm up drills. Make sure you are stretched and warmed up before getting into the practice session.
  • Vary your practicing and forget what the test requires. Instead of setting up targets at 30, 40 and 50 feet try setting up targets at different distances and at different angles rather than just on top of your tape. If you can consistently hit targets at any distance up to 50 feet then you will have a lot more confidence in your ability to perform this task during the test. Some of my fellows take a number of tennis balls and toss them out onto the field as their targets for their practice session.
  • Don’t worry about meeting the minimum requirements of a task but concentrate on meeting the requirements with ease. You are required to cast 85 feet – is that your personal best? If so, then don’t count on adrenaline to get you across the line in the test. Continue practicing until you can hit 90 or 95 feet consistently with minimal effort and with the line landing straight.
  • If one of your casts is giving you a problem then break it down into smaller parts and identify the things that are giving you problems. Fix these items and then put it all back together. You might recognize this as a form of Whole-Part-Whole. It works for your students and it works for you as well.
  • Work with your mentor to identify the areas to concentrate on and what sort of practice drills might help you fix an issue. Revisit the Baker’s dozen and see how they apply to practicing with a purpose.
  • Set aside a time to practice each day stick to it. If you set a regular time you are more likely to stick to practicing each day. Make sure people know that this is your time for practice and that you should not be disturbed. But don’t let your schedule become too much of a habit – vary your times on occasion. If you become mentally conditioned to making your best efforts at a certain time of day you may find your test time is not optimal for you.
  • Make sure you revisit the things you don’t concentrate on regularly to ensure you continue to improve or don’t backslide in those areas.
  • Train. Don’t strain.

Preparing for a casting certification test can be difficult because you need to practice a broad range of skills and it can be hard concentrate on one or two things. When I first began working towards becoming a certified instructor I printed out the performance test, took it to the field and worked my way through each task every time I practiced. After a couple of weeks I found that I spent about 10 minutes each session running through the parts of the test I felt mildly interested in and then spent the rest of my session trying to see if my distance cast had somehow improved from the previous day. Instead of my casting improving it became very sloppy. My loops were large and I was constantly ticking the grass. I was in no condition to attempt the test. At some point I decided that if I was going to pass the test I needed to concentrate on what was really required. Instead of spending every day trying to cast farther I concentrated on increasing the distance for which I had good loop control. If I started each session and found that I could easily handle the distance from the previous day then I added 1 or 2 feet for that session – no more than that. If I felt the loops weren’t up to my satisfaction I shortened the line until I felt I was back in control. By changing my practice methods I found that within a few weeks my casting, and my best distance, improved significantly. It takes patience but it pays off in the long run. Instead of running through the test every day you should run through it every few weeks to identify what things you need to concentrate on for the upcoming weeks. Select a limited number of items you think you can improve and stick to those.

One more tip – review your equipment regularly as well. Make sure you are getting the performance you need from the equipment you have selected and that it is kept in peak form.

Train Don’t Strain

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We tend to think of fly casting as a low stress physical activity so the likelihood of injury is low (with the exception of being hit with a hook perhaps) but in reality injured wrists, elbows and shoulders among those who are preparing for their master certification are quite common. Most candidates will spend a year or more practicing for an hour or more each day as they prepare for the test. This typically leads to injuries that are gradual onset in nature but sudden onset injuries happen as well. If you have spent several months preparing it is hard to back off when an injury occurs. It is also common to increase practice sessions significantly as the test draws near.

In order to prevent injuries there are some precautions you should take:

  • warm up prior to practicing. Begin with stretching, short casting, or light resistance exercise.
  • stay within your capabilities. If you’ve never cast anything heavier than a 5 weight rod don’t jump to a 13 weight to increase your strength. When practicing distance casting try to maintain good form rather than attempt to hit a new personal best in every workout.
  •  increase your workouts gradually. Add a few minutes to your workout each week or increase rod weight gradually over the course of several weeks or months. Don’t be fooled here – you may feel fine after adding 15 minutes or a half hour to your regular practice sessions but remember that many of the injuries you will experience are gradual onset in nature. It may take days or weeks before you begin to experience pain and by then it may be too late to simply back off.
  • don’t train to your maximum every day. It’s tempting to finish every practice session by seeing how far you can cast but you will do better by limiting these sessions to once or twice per week.
  • aim for smoothness and avoid jerky movements.

Learn to take frequent breaks. If you experience pain then it’s time to call it a day. If the pain persists for a few days then you should consider seeing your doctor.

Finally, if you do experience an injury, you should book a few sessions with a casting instructor after your recovery to get advice on things you may be doing wrong.

Stay healthy and enjoy the journey.

Glossary of Fly Casting Terms

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In addition to the definitions for casting terms provided by the Casting Education Committee the following terms are relevant for casting instructors or those who are considering a certification test. The list is my own and is by no means to be considered complete. These are the terms only and definitions are not included as there are no Casting Certification Organization Approved definitions for these terms. I have included reference sources where definitions for these terms, and many others, can be found.

  • 180 degree rule
  • association
  • casting mechanics (the 5 essentials)
  • casting plane
  • change of direction cast
  • chunking
  • cognitive overload
  • concave path
  • convex path
  • counterflex
  • covering vs teaching
  • D loop
  • dangle
  • distributed practice
  • doming
  • energy
  • fast rod
  • fly leg
  • fluorocarbon
  • force (f=ma)
  • kinetic energy
  • leg
  • Lift
  • line plane
  • loop velocity
  • minimum chord length
  • monofilament
  • muscle memory
  • over powered curve
  • overhang
  • pause
  • pick up and lay down cast (aka puld or puald)
  • plane
  • potential energy
  • power
  • praise, prompt, leave
  • puald – aka pick up and lay down cast
  • puld – aka pick up and lay down cast
  • rebound
  • recency and primacy
  • river left
  • river right
  • rod action
  • rod flex
  • rod leg
  • rod plane
  • rod straight position
  • RSP – aka rod straight position
  • running line
  • say-see-do
  • sequencing
  • shooting head
  • six step method
  • slack
  • slide loading
  • slow rod
  • SLP – aka straight line path
  • spey cast
  • spine (aka spline)
  • staircasing
  • stop
  • straight line path
  • style
  • substance
  • switch cast
  • the five essentials
  • thrust
  • timing
  • tracking
  • trajectory
  • Under powered curve
  • whole-part-whole
  • X ( a North American term for leader and tippet thickness)

You can find definitions for these terms at the following locations on line. Be aware that the definitions may not always agree.

– http://www.hooked-on-flies.com/glossary.htmhttp://macbrownflyfish.com/fly-casting-definitions/

– http://fedflyfishers.org/Resources/Education/FlyFishingGlossary.aspx

– http://www.fieldflyfishing.com/resources/glossary.html

– http://forums.ozarkanglers.com/topic/9037-glossary-of-fly-casting-terms/

– http://www.wildoutfitting.com/mci/emailarchive/mlistarchive/doc01Yrh9nQPi.doc

– The Baker’s Dozen – article by Dayle Mazzarella

A Picture is Worth a Thousand Words by Peter Glasson

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I received this from Peter Glasson in response to my rather wordy description of the casting stroke and the stop. I think it is an excellent diagram that contains many of the terms and expressions we use as casting instructors to describe the casting stroke.

[PG] A picture is worth a thousand words.

[embeddoc url=”http://wildoutfitting.com/testwp4920/wp-content/uploads/2015/04/casting1of3.pdf” download=”all”]

Teaching Old Dogs New Tricks – by Dayle Mazzarella

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I received the following from Steve Smith: [SS] Walter great article today in the Globe and Mail about teaching. It is in the Globe life section Mon.Mar.9th.They are talking about skiing but it could be any sport. It starts with are you a watcher, thinker, feeler or doer. I don’t know how to copy it and share (as I get it electronically ) but I’m sure you do, anyways it is a good read. Steve [WS] Thanks Steve! The article can be found by clicking on this link: http://www.theglobeandmail.com/life/health-and-fitness/fitness/tremblant-ski-school-teaches-old-dogs-new-tricks/article23338383/ I asked our resident expert on teaching theory, Dayle Mazzarella, for his thoughts about this article. Here is what he had to say: [DM] I’ve a few things! 1. The Canadian Ski article

a) Roger Castonguay’s “style” of teaching by his own admission, only works with very advanced or very talented individuals. That is not a style of teaching anyone should emulate. It is seriously limited in its effectiveness.

b) Anyone can learn using Kathy Prophet’s “style” – including the people Roger can reach. Her style, which is organized, sequential, and detailed, works with anyone.

c) A style that reaches only a relatively small percentage of the population is like having a cast that only reaches a few of the potential fish. Would we teach it?

The paragraph “There is not empirical evidence supporting … matching learning style and teaching style” is supported by the attached article, “Are Learning Styles a Symptom of Education’s Ills”. [WS] See attached document at end of this article[WS] 2. Style vs Substance: Whole – Part – Whole Teaching is virtually the only methodology supported by research insuring optimal learning for all students. Following is the substance of good teaching embodied in a whole-part-whole methodology:  (How one does this is style.)

a) Explain and/or demonstrate what you want the student to know or do by the time the lesson is done.  (How one does this is style.)

b) Explain and/or demonstrate what past knowledge and/or skill will be used as a building block. Explain and/or demonstrate how the  new skill will be used in the future. This is called motivation – “what’s in it for me” and “what do I know that will help me do this more easily and make it less intimidating”. (Often referred to as the anticipatory set.) The whole is completed, putting the parts to follow in context.  (How one does this is style.)

c) Break the skill and/or knowledge down into as many separate components as possible – (structured practice). Explain and/or demonstrate each step separately in a sequential manner.   ( How one does this is style.)

d) Now have the student do each of the steps in a very closely controlled environment so that errors are minimized. This step is usually, in the case of casting, done by having the student pantomime the steps with the instructor. For most students, this step requires lots of repetitions.  ( How one does this is style.)

e) Now have the student teach those steps to someone.

f) Have the student “put it all together”. Students begin putting it all together so that each step “flows” seamlessly into the next.  Do the “whole” skill.

g) Have the student practice the new skill 7 or 8 times over the next several days.

Style is how one does those steps! It is about what analogies one uses, which props, which “tools” in their bag they use while following the basic sequence. For instance, in the structured practice, an instructor may choose to have the student use a rod and line, a rod with no line, half a rod, a pool noodle, a paint brush, a pencil, etc…. The instructor may use pantomime, or have the student simultaneously do the steps with the instructor. These are examples of style. Following the basic steps above are not style issues for someone who wishes to become an exceptional teacher, any more than the 5 Essentials are style issues for those aspiring to become optimal casters. Every piece of research we have in the past 30 years continues to support the above methodology as the basis for optimal instruction. Virtually every successful coach in any sport, from high school to professionals, follow these basic principles of good instruction. Dayle [WS] Thanks Dayle and Steve! The document mentioned by Dayle can be found below: [embeddoc url=”http://wildoutfitting.com/testwp4920/wp-content/uploads/2015/03/LearningStylesResearch.pdf” viewer=”google”]

Superman vs The Flash, Force vs Power

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Force vs power or torque vs power is a difficult concept for many people to understand. Most people who have an interest in cars will have an idea but have a hard time explaining it.

In our Superman vs the Flash analogy, Flash is the only person who is faster than Superman but Superman is capable of generating far more force than the Flash. We know that F=ma which means a=F/m so we should expect Superman to always win in a race. More force equals more acceleration equals greater speed. Right?

So why does Flash win in a race if Superman is capable of generating far more force than Flash?  Is this just comic land ignoring real world physics or is thus scenario possible in real life?

The answer is in the relationship between force, work, energy and power.

If I apply force to an object and get it moving I am doing work on the object. The amount of work I do on the object  is equal to the force I apply times the distance I apply the force (W=fd). When I do work on an object I change its kinetic energy by the amount of work I do on the object. Let’s say I apply one Newton of force on an initially stationary 1 kilogram mass for a distance of 1 meter.  Ignoring gravity and losses due to friction I will do one Joule of work on the mass and, hence, raise its kinetic energy to 1 Joule. Since we know the mass of the object is 1 kg we can determine its final velocity with the formula KE=1/2 mv^2. The velocity of the mass is now roughly 1.4 meters/sec.

The final velocity of the mass is directly related to the amount of work I do on the object. If I do that work in 1 second or 2 seconds it doesn’t matter, the final velocity will remain the same.

This is where power comes into the discussion. Power is the rate at which I do work on an object, i.e. P=W/t. If I do 1 Joule of work on an object in 1 second I will be applying twice as much power than if I do 1 Joule of work on the object in 2 seconds. In the first case my power output is 1 watt, or 1 joule/s, because I increased my energy level to 1 joule in second. In the second case my power output is only 0.5 watts because I increased my energy level by 0.5 joules for two seconds for a final energy level of 1 joule.

Think of power as the ramp up rate of energy and the amount of energy I give to an object determines how fast the object will end up moving. Power is how fast I increase the energy of the object.

Okay this is still confusing because if I apply more force to an object I give it more acceleration and it gets up to speed that much faster so more force still means a greater increase in energy in a shorter amount of time. How is force different from power? And why do I care?

This is where the car buffs say, “But the amount of force (torque) my vehicle can apply to the road varies with how fast my vehicle is moving. The faster my car is moving the less torque it can exert.”

Bingo!

When we measure a person’s strength we measure how much force they are able to exert against an unmoving or slow moving object. When we measure a person’s power we look at how much force they are capable of exerting against an object that is in motion. We measure that value at various speeds and generate a power curve, i.e. how much force can I exert on an object that is moving at various velocities.

A typical power curve for a person can be found here:

Muscle Force Velocity Relationship

This is similar to the automobile analogy where a truck built for towing can exert far more force than a race car on a stationary or slow moving object but the race car is capable of far greater speeds. This is because the amount of force the truck is capable of exerting with its tires on the road (i.e. torque) decreases rapidly as its speed increases. The amount of torque the race car exerts also decreases as its speed increases but not as rapidly as the truck. At speeds of a little over a hundred miles per hour most trucks are only capable of exerting enough force to overcome drag and friction in order to keep the truck moving at a constant speed. The race car on the other hand continues to exert sufficient force to overcome drag and friction and to continue accelerating up to speeds in excess of 200 mph. When the race car reaches its maximum speed it too will top out and will only be able to continue at that speed without further acceleration.

Since power is equal to force times velocity (P=Fv) , at lower speeds the truck has more power but at higher speeds the race car has more power.

When it comes to casting we have another factor to consider. The time it takes to reach peak force. I may be physically much stronger than someone else but if someone else is faster than I am they will reach their peak force more quickly than I will. In casting we want to reach peak force quickly and then continue to apply a constant force to the rod for the duration of the casting stroke until we stop the rod butt. This was described by Bruce Richards in his article about Casting Analyzer Traces. If we take too long to reach our peak force the resulting casting analyzer trace will show a lack of “smoothness” resulting in tailing loop.

For most casting that we do we are capable of reaching the desired force for our casts quickly enough to be smooth and we have sufficient power to generate the line speed we need. These items are more of interest to distance casters or anyone looking to increase their distance cast.

How does one increase power and improve time to peak power for distance casting? I think that is a subject for a separate post which I plan to work on later.