Acceleration

Walter & Group...

From Aitor Coteron  :

Hi Gordy,

Some comments about acceleration on fly casting.

IMO most instructors dont have a good grasp of some basic concepts of physics; the difficuties in understanding the differences among speed, velocity and acceleration is an example of that.

The problem is that to understand the basics of how fly casting works those concepts are capital. Fortunately you don't have to be Eisntein to understand them (they are taught in school to 12 year old children so it isn't rocket science).

Constant acceleration means that the rate at which velocity changes is constant.

If a body is moving at a constant speed of 3m/s and at a given instant we apply an acceler. that remains constant and, as a result, the speed of the body in the next second is 4m/s, 5m/s in the next second, 6 m/s in the next second, 7m/s and so on, we have applied a constant acceler. of 1 m/s/s.

A non constant acceler., one which doesn't remain the same but increases instead, could give this result in the speed of the body:

4m/s, 6m/s, 9m/s, 14m/s, 21m/s ...

A perfect constant acceler. doesn't exist but an example of one that gets very close to constant is acceleration due to gravity.

If we place a rod with its butt fixed horizontally to a table top and hang a weight from its tip the rod gets bent. That bend doesn't change since the acceler. due to gravity is constant (9.8 m/s/s) what results in a constant force applied to the rod tip.

A constant acceler. applied to a mass that remains constant equals a constant force (F = M x A). During a casting stroke the mass doesn't change, if we apply a constant acceler. to the rod butt the force exerted against the rod tip is constant also so the bend in the rod doesn't increase.

I am not taking into account that the angle between the rod and the line changes during the stroke and that has interesting effects, but this reasoning is enough for now to understand the basic concept of acceler. and its implications on fly casting.

Sorry if this has been discussed before, I haven't have time to read the last posts yet.

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Aitor...

Your message helps a great deal because it places the information before us once again using different word pictures.  A good teaching technique.

It serves to reinforce the material presented in prior attachments by Bruce Richards, Mark Milkovitch and the fly casting physics material so well written by Walter Simberski. 

Here is a simplistic physics concept which sometimes helps students understand words such as "velocity", "acceleration" and "inertia" :-

Speed in a particular direction is called velocity.

Rate of increase in velocity is acceleration.

When the fly rod is moved at a constant velocity , it will not bend or load.

The rod will only bend when it is moved ever faster in a particular direction against some resistance.  That is the effect of  acceleration.

 The resistance is provided largely by the tendency of the fly line to remain where it was.  That is called inertia.*

When the rod is moved at the same rate of increase in velocity, we call that constant acceleration.

 

* One way of describing inertia:    Bodies at rest tend to remain at rest ; bodies in motion tend to remain in motion.

Gordy

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From Stephan Siikaavara :

Hi Gordy!

I read Bruces comments on acceleration and I wonder why you suggest a constant accelleration would be more efficient than a exponential acceleration?

 

When I cast something, a rock, a ball of whatever, I do not feel that the most efficient way to do it is by accelerating the object in a constant manner? I think I peak the acceleration pretty clearly exponential once the cast starts to involve my elbow and wrist joint. Do spear casters accellerate in a constant manner and how about baseball pitchers?

 

Do the most efficient flycasters use constant acceleration for longer casts? I wonder beacuse the ones that can make the longest casts in our group here in Piteå don´t. We also get the sharpest loops for medium distance work with smoothness rates around 11-15, is that normal? One of the guys here can false cast with 105 ft of line measured without leader with very nice, tight and consistant loops but his smoothness during that cast is only around 25, how should we interpret that?  

 

Best regards

Stefan

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Stefan...

That is what I used to think, also.

At that time I taught this as, "accelerated acceleration" until our physicists told me that this is not a proper term to describe what is happening .

I still "feel" that this is what I'm doing when making my best distance casts ...... but the folks who have actually measured and studied these motions tell me that it really isn't the case.

I believe Bruce Richards and Noel Perkins have shown with their equipment (including the Casting Analyzer) and formulae that once the caster deviates from near constant acceleration the loops suffer.

That makes me wonder if you and your Group at Pitea have actually measured and plotted out the acceleration curves achieved with those casts.  I'd like to learn your method used to measure smoothness.

I'm pushing the limits of my mathematical ability when I ask myself, "Can we have exponential acceleration as constant exponential increase in velocity ?"

I'm not qualified to go any further than this with my comments since I didn't actually take any measurements.    SO :

Let's ask Bruce.

Perhaps Walter Simberski (our mathematician) will comment on my question.

Gordy

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