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From: Catrike Ryder <Soloman@old.bikers.org>
Newsgroups: rec.bicycles.tech
Subject: Re: fast tires
Date: Thu, 19 Jun 2025 15:55:34 -0400
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On Thu, 19 Jun 2025 14:25:57 -0500, AMuzi <am@yellowjersey.org> wrote:

>On 6/19/2025 1:46 PM, Catrike Ryder wrote:
>> On Thu, 19 Jun 2025 14:20:34 -0400, Radey Shouman
>> <shouman@comcast.net> wrote:
>> 
>>> Catrike Ryder <Soloman@old.bikers.org> writes:
>>>
>>>> On Wed, 18 Jun 2025 12:58:56 -0400, Frank Krygowski
>>>> <frkrygow@sbcglobal.net> wrote:
>>>>
>>>>> On 6/18/2025 11:20 AM, AMuzi wrote:
>>>>>> On 6/18/2025 10:13 AM, Radey Shouman wrote:
>>>>>>> Frank Krygowski <frkrygow@sbcglobal.net> writes:
>>>>>>>
>>>>>>>> On 6/17/2025 1:05 PM, Radey Shouman wrote:
>>>>>>>>> Frank Krygowski <frkrygow@sbcglobal.net> writes:
>>>>>>>>>
>>>>>>>>>> But OK, I can probably cram in that 98 pounds = 7 stones.
>>>>>>>>> "7 stone", not "7 stones".
>>>>>>>>
>>>>>>>> Huh. OK, I can try to remember that too.
>>>>>>>>
>>>>>>>>>> (Do they have an actual stone stored away somewhere, like they used to
>>>>>>>>>> have an actual kilogram?)
>>>>>>>>> No idea.  Different scales of weight for different items was once
>>>>>>>>> considered natural. Troy ounces and pounds still survive.  12 Troy
>>>>>>>>> ounces per pound, of course.  "Grain" for gunpowder or drugs is also
>>>>>>>>> still in use, although in the case of drugs I think it's mostly just
>>>>>>>>> aspirin labels.
>>>>>>>>
>>>>>>>> The SI system is _so_ much more logical!
>>>>>>>>
>>>>>>>> Although users often make the inverse of our usual force vs. mass
>>>>>>>> mistake, by using kilograms as a measure of force.
>>>>>>>
>>>>>>> True, ordinary everyday SI users almost always use Kg as a unit of
>>>>>>> either mass or weight interchangeably.  Maybe when we live on different
>>>>>>> planets the difference will be more intuitive.
>>>>>>>
>>>>>>
>>>>>> Like sidereal time.
>>>>>>
>>>>>> Is there a problem here at roughly sea level on earth where weight vs
>>>>>> mass discrepancy is significant?  I really don't know.
>>>>>
>>>>> The problem arises in engineering calculations - things like "How much
>>>>> force will be required to accelerate this component at this given
>>>>> acceleration?" An example might be the force a valve spring must exert
>>>>> to close an intake valve on time.
>>>>>
>>>>> As Radey said, engineers working with U.S. units usually distinguish
>>>>> force and mass by use of the terms "pounds force (lbf)" and  "pounds
>>>>> mass (lbm)" where the "f" and "m" are subscripts. And then they use the
>>>>> poorly understood (by students, anyway) conversion factor
>>>>>
>>>>> 32.2 lbm*ft/(lbf*s^2) to work out the correct units.
>>>>>
>>>>> (A conversion factor is an algebraic expression with a value of one. For
>>>>> example, twelve inches = one foot expressed as a fractional conversion
>>>>> factor is (12 inches/1 foot)  Since numerator equals denominator, its
>>>>> value is one - it doesn't change the magnitude of an answer - but it can
>>>>> be used to change the answer's form.)
>>>>>
>>>>> Here's a simple example: What would be the acceleration of a 1 lbm
>>>>> object if a 1 pound force were applied to it?
>>>>>
>>>>> Using F=m*a and solving for acceleration gives a = F/m
>>>>>
>>>>> And plugging in a = 1 lb / 1 lb gives an answer of one...
>>>>> somethings?Maybe one ft/s^2? That would be a typical freshman mistake.
>>>>>
>>>>> But keeping track of units properly, the calculation should be
>>>>> a = 1 lbf/1 lbm, and the units are not working out to ft/s^2. So apply
>>>>> the conversion factor:
>>>>>
>>>>> a=(1 lbf / 1 lbm) * 32.2 (lbm*ft)/(lbf*s^2)
>>>>>
>>>>> which leads to units cancelling properly in the overall numerator and
>>>>> denominator, leaving the answer as a = 32.2 ft/s^2
>>>>>
>>>>> IOW if you turn an object loose with only its weight acting on its mass,
>>>>> it accelerates downward at one "gee."
>>>>
>>>> Count me unimpressed by Krygowski's cut and paste.
>>>
>>> I'm reasonably sure that was written extemporaneously.  Any engineering
>>> professor should be able to do the same.  Any practicing engineer will
>>> have gone through the same reasoning many times.
>> 
>> I'm reasonably sure he copied out of a book.
>> 
>> --
>> C'est bon
>> Soloman
>
>Why?  For similar paragraphs in my field I can do that all 
>day long extemporaneously. As can Mr Shouman.  Or anyone in 
>his own skilled field.

Well, he is good at remembering stuff being a learn by rote guy, I
just don't believe he could write it out without help.

--
C'est bon
Soloman