Re: fast tires

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