Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Catrike Ryder Newsgroups: rec.bicycles.tech Subject: Re: fast tires Date: Thu, 19 Jun 2025 15:55:34 -0400 Organization: A noiseless patient Spider Lines: 106 Message-ID: References: <102hega$3gh36$1@dont-email.me> <87y0trega6.fsf@mothra.hsd1.ma.comcast.net> <102qn1c$2495c$10@dont-email.me> <8734by47tk.fsf@mothra.hsd1.ma.comcast.net> <102smlf$2koi8$2@dont-email.me> <87msa5gk1j.fsf@mothra.hsd1.ma.comcast.net> <102ulf8$35v0c$2@dont-email.me> <102ur8h$37k89$7@dont-email.me> <87msa3ioel.fsf@mothra.hsd1.ma.comcast.net> <1031o85$2t6n$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Injection-Date: Thu, 19 Jun 2025 21:55:37 +0200 (CEST) Injection-Info: dont-email.me; posting-host="babbc3c360229af554d8c6f654de1a79"; logging-data="114731"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/Y7JmjkIcdSI9VIWDjsskUwtHRTovCEEg=" User-Agent: ForteAgent/8.00.32.1272 Cancel-Lock: sha1:BRUvSePH+ChBtuK0aL8pVkIW0e8= On Thu, 19 Jun 2025 14:25:57 -0500, AMuzi wrote: >On 6/19/2025 1:46 PM, Catrike Ryder wrote: >> On Thu, 19 Jun 2025 14:20:34 -0400, Radey Shouman >> wrote: >> >>> Catrike Ryder writes: >>> >>>> On Wed, 18 Jun 2025 12:58:56 -0400, Frank Krygowski >>>> wrote: >>>> >>>>> On 6/18/2025 11:20 AM, AMuzi wrote: >>>>>> On 6/18/2025 10:13 AM, Radey Shouman wrote: >>>>>>> Frank Krygowski writes: >>>>>>> >>>>>>>> On 6/17/2025 1:05 PM, Radey Shouman wrote: >>>>>>>>> Frank Krygowski 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