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Lower hand versus upper hand

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Paul Arden
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Post by Paul Arden »

No, the ratio of force between top and bottom hand are fixed for grip width and rod length with fixed bend.

I'm completely lost. Can't I just apply all the power with the top hand - for example. In which case it would be 100% top hand and 0% bottom hand. I do that all the time with single handed dildos.
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Post by Magnus »

Can't I just apply all the power with the top hand... I do that all the time with single handed dildos.


Thats why they're called single handed?

No. The geometry Sakari is describing holds true for SH rods too just the distance D1 is shorter and the ratios are different.

In the case of 'all top hand' with a DH rod. What we call 'all top hand' means roughly the top hand moves and the lower hand stays still - but the same forces or at least the same ratio of forces applies to the hands whether one hand moves or they both move. (If I hold my hands still and a 5N force is applied at the tip, as in Sakari's diagram, the forces at my hands will be? 40N at the top hand and 35N at the bottom!)
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Paul Arden
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Post by Paul Arden »

So this \\\\/ , \.../ and X are the same?
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Post by Magnus »

From the perspective of the forces at the hands - all else being equal - and it isn't - yes.

But consider the distance the force has displaced - work by the tip on the line in each of those cases.

With due respect to the technical guys - physicists and engineers. This is what I mean about their insights being 'misleading'. I dunno if you class yourself as a layman, Paul. I would have thought one of the more clued up - and this stuff confuses you.
To be honest I wonder how helpful some of the deep and meaningful technical threads really are. We end up in a situation where the geeks come to their conclusions and since few (other) people have the least clue what they mean or how they arrived at their conclusions - laymen end up having to take their insights as gospel. I'm using the term gospel there because it's about belief not about insight or reason.
And it gets worse when the geeks don't agree. Are you with Gordy and Merlin or with Grunde and Server about retarding torque and unloading?
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Post by Paul Arden »

Just so I understand this correctly, if I strap my top hand to my shoulder with some Xmas Sellotape, and apply the rotation by pulling the bottom hand, the force proportion is the same as if I attach my bottom hand to my belt buckle and push with the top hand?

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Post by Paul Arden »

And it gets worse when the geeks don't agree. Are you with Gordy and Merlin or with Grunde and Server about retarding torque and unloading?

I'm not with anyone until they agree.
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Post by Magnus »

Paul Arden wrote:Just so I understand this correctly, if I strap my top hand to my shoulder with some Xmas Sellotape, and apply the rotation by pulling the bottom hand, the force proportion is the same as if I attach my bottom hand to my belt buckle and push with the top hand?

Thanks, Paul
Yes.
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Post by Paul Arden »

I don't believe this. We need a couple of spring balances.

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Post by sms »

Make sure the spring balances do not need to be accelerated much as their inertia may disturb the results (or at least make the results harder to interpret). Or use as light ones as possible.

Blimey, I thought I posted one before already but cannot it is not here? Re-try...
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Post by sms »

Retry, had to rewrite the whole thing.
We get closer. But there is still a missunderstanding here.

First of all I did not refer to Newton. I just put out some numbers (without units).

Also I did not want the rod bent to be the same since it never is the same when I help a student to change his casting technique.

Bernd,
it does not matter, I linearized them. In first case 80% top hand, 20% lower hand and in second 55,6% top and 44,4% lower. The only way to change the ratio is change the grip width or bend (effective length) of the rod.

In the case of 'all top hand' with a DH rod. What we call 'all top hand' means roughly the top hand moves and the lower hand stays still - but the same forces or at least the same ratio of forces applies to the hands whether one hand moves or they both move. (If I hold my hands still and a 5N force is applied at the tip, as in Sakari's diagram, the forces at my hands will be? 40N at the top hand and 35N at the bottom!)

Bernd and Magnus,
my conclusion is that using term force is not good for teaching due this. Movement, that relates to work or effort, which is related to what we feel how much we are working, are much better tools and not uncorrect technically.

Just so I understand this correctly, if I strap my top hand to my shoulder with some Xmas Sellotape, and apply the rotation by pulling the bottom hand, the force proportion is the same as if I attach my bottom hand to my belt buckle and push with the top hand?

Paul,
another yes.

With due respect to the technical guys - physicists and engineers. This is what I mean about their insights being 'misleading'. I dunno if you class yourself as a layman, Paul. I would have thought one of the more clued up - and this stuff confuses you.
To be honest I wonder how helpful some of the deep and meaningful technical threads really are. We end up in a situation where the geeks come to their conclusions and since few (other) people have the least clue what they mean or how they arrived at their conclusions - laymen end up having to take their insights as gospel. I'm using the term gospel there because it's about belief not about insight or reason.
And it gets worse when the geeks don't agree. Are you with Gordy and Merlin or with Grunde and Server about retarding torque and unloading?

Magnus,
yes, the results do not nearly always help "layman" - at least directly (the gospel). I think understanding what happens is not a bad thing. But, I do agree that it is not for everybody and often it doesn't correlate what people think they are doing for example - video is a bitch in that aspect too (Hey, I didn't do it like that and still it is on tape!). So, the gospel should be translated in a form that is not technically incorrect, but still helpful and meaningful for the layman. And that is difficult and will pretty much always still lead to misunderstandings to some extent.

For me personally, slowed down videoanalysis of my DH forward cast has helped me to change small nuances that I would have had trouble to change correctly without the video and physical understanding of casting. It is especially useful when one has to make compromises - the right balance choise is much easier.

Btw, in my opinion the retarding torque myth is busted. We have two different hypotheses on what happens and only the other is backed up by experiments (video again).
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Post by Magnus »

Hi Sakari

Since most people probably don't understand the technical meaning and use it metaphorically anyway I doubt it really matters if they say 'force'. My preference would be 'effort' supported by movement and work.
If someone asks why a stationary hand resisting a force is doing no work I'm sending them to you :D

I think understanding what happens is not a bad thing.

I'd go further - understanding is a good thing. (Damned Liberal upbringing!) Where it goes sour is the way concepts are explained, or not, and, too often, the way laymen trying to understand are treated by geeks when they have the nerve to open their mouths. In some situations even asking a question gets you slapped with patronizing comments at best or attempts to humiliate at worst.
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Paul Arden
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Post by Paul Arden »

Well I don't understand this because I can conceivably push with the bottom hand instead of pull, but at a slower rate, and the rod will still rotate. That's force in the opposite direction to how we normally throw a DHD. You're saying that this is not possible. :???:

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Paul
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Post by Magnus »

Nope that's perfectly possible - force goes in the opposite direction so maybe call it a backcast?
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Post by Lasse Karlsson »

Hi magnus

I think paul means both hands are pushing in the same direction :)

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Post by Bernd »

Hi everyone,

"effort" is a word which I wouldn't understand by myself. Had to look it up right now but still don't really feel I fully understand how I may use it for getting the message to the student. :(

What would you tell your student if you want him to be more pronounced with his bottom hand and less with top hand?

Thanks
Bernd
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