Re: [Paddlewise] Pro's and Con's of the "Swede Form"

At 5:33 PM -0700 6/7/99, Bob Myers wrote:
>On Jun 7, 16:51, Bob Myers wrote:
>} Subject: Re: [Paddlewise] Pro's and Con's of the "Swede Form"
>> On Jun 6, 15:26, Nick Schade wrote:
>> } Subject: Re: [Paddlewise] Pro's and Con's of the "Swede Form"
>> > At 8:02 AM -0400 6/4/99, John Winters wrote:
>> >
>> > >You know me, "If you can't measure a thing you don't know much about it".
>> > >:-)
>> > >
>> > >Actually I didn't think that up. It comes from Lord Kelvin who said, "If
>> > >you can measure that of which you speak, and can express it by
>>number, you
>> > >know something of your subject. But if you cannot measure it, your
>> > >knowledge is meager and unsatisfactory."
>> >
>> > Now we're getting into philosophy of science. If something is not
>> > measurable, does it still exist? I can not measure the mass of an
>>electron,
>> > yet I am willing to accept that it has a mass. I don't see why the noise
>> > produced by a tree falling in the forest is dependant on the
>>sensitivity of
>> > my ear.
>>
>> But the mass of an electron can and has been measured, and it is useful
>> information to those working at that level.
>>
>> The noise produced by a tree falling in the forest is not dependent on
>> the sensitivity of your ear.  Your *knowledge* of the noise is, however.
>>
>> The question is not of existence of things you cannot measure; the
>> question is of your knowledge of things you cannot or have not measured.
>
>I should really make sure I go back and read the full thread before I
>respond to these.
>
>The original discussion was about wave-making resistance of a submarine.
>
>I do agree with John that if something has an effect so small it is
>not detectable, that it really makes no difference whether or not it
>exists or not - for all practical purposes it does not.
>
>If you've studied or worked with science or engineering to any significant
>degree, you know that there are lots of times that we have to make
>"simplifying assumptions" - ignoring very small effects to make the problems
>tractable.   This is a primary method of both science and engineering.
>(You usually do need to show that the effect can be neglected, though.)
>
>It is pointless, and indeed entirely unscientific, to argue about
>whether undetectable events are real or not - you just don't know
>until you *can* detect it or its absence.  Otherwise, yes, you are
>going beyond the bounds of science - science is about what you can
>detect and measure.
>
>The 'tree falling' example does not fall into this category - you
>can still detect a tree falling even if you're deaf.  It is easy
>to infer that it made a noise when it fell.  There are lots of
>detectable events associated with this.
>

Ignoring a factor because it is too small to be significant and ignoring it
because you don't think it exists are two very different propositions. To
say that a submarine 3 diameters below the surface experiences no surface
drag is different from saying a submarine 3 diameters below the surface
experiences negligable surface drag.

What happens when two submarines cruise next to each other at 3 diameters
below the surface.? How close do they have to be before they produce a
non-negligable surface drag. If your knowledge says "3 diameters -> surface
drag = 0" then you have no reason to suspect that there would be any
surface drag until they touched. Where if your knowledge says "3 diameters
-> surface drag >0" you might choose to investigate further. Or what if the
sea floor is 4 diameters down? The  interaction of 2 or more undetectable
reactions may be detectable, and may even be significant. It does not help
your knowledge to dismiss undetectable reactions as non-existant.

Rules of thumb only work as long as they are being used within the scope of
their assumptions. If you follow a rule of thumb without knowing the the
science behind the assumptions and the limitations of those assumption, you
only have enough knowledge to be dangerous. If you know the science behind
the rules, you have enough knowledge to safely make your own assumptions
and you can detect when the rules no longer apply.

Saying "Waves cause drag" is a good enough rule of thumb in many cases
because waves are a symptom of drag and if the waves disappear so has the
drag. But it could lead to the conclusion that paddling in an environment
where waves can not exist would eliminate the drag. This is not the case.
What you really want is to eliminate imparting any net velocity to the
water and the waves will disappear as a side effect.



Nick Schade
Guillemot Kayaks
10 Ash Swamp Rd
Glastonbury, CT 06033
(860) 659-8847

Schade_at_guillemot-kayaks.com
http://www.guillemot-kayaks.com/

>>>>"It's not just Art, It's a Craft!"<<<<


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