Constant Acceleration

[Paul Arden]

Hi folks,

I know we had a discussion on this before but the board search function ignores common words such as acceleration

When I look at the acceleration graphs I see a curve not a straight line. To get “constant acceleration” the beginning of the cast is ignored. Now one could say it’s because we are human. Or perhaps it’s because we need to start the stroke slowly?

Anyway I regularly hear instructors talk about the need for constant acceleration. What do the members of this forum think about this?

Many thanks,
Paul

[VGB]

Depends what you mean by constant acceleration. In my experience, it means whatever the speaker wants it to. I don’t use it.

Regards

Vince

[Graeme H]

I can't remember what my graphs showed but I think it didn't matter and rarely occurred. (We are talking about constant acceleration of the line, aren't we?)

To get around that annoying search "feature", type this into a google search: acceleration site:http://www.sexyloops.co.uk/theboard

Cheers,
Graeme

[Graeme H]

Here ya go:

http://www.sexyloops.co.uk/theboard/vie ... php?t=3043

[Mangrove Cuckoo]

Depends what you mean by constant acceleration.
Vince

Yeah... this should be fun!

I think the term is ambiguous at best, and probably not what most non-physicists think it means... and I am not a physicist so I'll let them try to explain.

But... I think the curve should be a curve, not a straight line... and I doubt, even with rotation and leverage, that a human is capable of achieving "constant" acceleration of the line. Well, not throughout the whole stroke. The importance of the haul to just maintain a constant speed seems to prove it?

[Dirk le Roux]

Hi Paul

"Constant acceleration" can only be constant in one of two ways -

• The acceleration remains constantly the same magnitude and its time plot (with time on the horizontal axis) is a straight horizontal. The resulting velocity plot is a straight slope

• The acceleration increases/decreases at a constant rate and its time plot is a straight slope. The resulting velocity plot curves like a parabola

The last interpretation is probably what is meant by those who use the term in fly casting, however humanly executable. I haven't seen straight-sloped velocity plots from real-life fly casts, but then straight lines/slopes already tend to idealise reality. Instructor talk about constant acceleration is in my view similar to instructor talk about SLP - a guideline rather than what is literally achievable, nor fully desirable.

My acceleration plots that Graeme referenced are unfortunately how Tracker calculates them, which yields increasingly more jittery charts the higher the derivative represented. They can be simplified in the reader's mind to cut through the jitter.

This graph from the Wikipedia page on Jerk may provide some perspective on the dynamics relationships:

NOT a physicist either, nevertheless trying to explain.

All the best,
Dirk

[jarmo]

Greetings.

Anyway I regularly hear instructors talk about the need for constant acceleration. What do the members of this forum think about this?

One recent thing related to this is Graeme's brilliant "top ferrule"-exercise, which I think provides an external cue for constant acceleration. Due to the good ole \(F=ma \rightarrow a=F/m\), if the mass \(m\) stays constant, a constant force \(F\) will yield constant acceleration \(a\). In Greame's exercise, the student needs to

put a bend in the rod at the top ferrule and keep it there as long as you can

This yields constant acceleration as it implies a constant force being applied to the line. To see this, consider having the rod in place and pulling the line with one hand, then keeping your line hand static once you reach a certain force level, that is, constant force: this will place a bend at a certain location in the rod, and the bend will stay the same as long as the force stays constant. Therefore, a "fixed bend" implies constant force and therefore constant acceleration.

[James9118]

I'm going to stick this here and see if people can figure out why I'd make this statement:

A constant acceleration* will cause a tailing loop.

*constant in terms of the definition above such that the velocity increase is perfectly linear.

James

[Graeme H]

What are we accelerating James? The line or some part of the rod?

Cheers,
Graeme

[Torsten]

Here you go:

https://www.sexyloops.com/articles/perfectloop.shtml

Quest for the Perfect Loop
by Bruce Richards

"- The rate of acceleration of the rod butt must be as close to the same at the beginning of the stroke as it is at the end. Yes, the rod will be going much faster at the end than the beginning, but the rate of acceleration should be constant in getting the rod from slow to fast. I know this goes counter to what many have said and written, and even to what many of us think we do, but ALL the best casters we've analyzed had very constant acceleration, regardless of what they thought they were doing."

Torsten.