gravity wrote:


i first heard of slugs at age 7, but i've never seen them used in an
engineering class.

we used SI almost exclusively in university and high school. i was taught
there that pounds is a unit of force (not mass). however Wikipedia claims
pounds is a standardized unit of mass, not force.


I don't care who says pounds is a unit of mass, they are wrong! If you
use pounds in a formula that wants mass, your answer will be WRONG.


--
Chris W
KE5GIX

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"Chris W" wrote in message
news:zcDlg.57805$9c6.18712@dukeread11...
gravity wrote:


i first heard of slugs at age 7, but i've never seen them used in an
engineering class.

we used SI almost exclusively in university and high school. i was
taught
there that pounds is a unit of force (not mass). however Wikipedia
claims
pounds is a standardized unit of mass, not force.


I don't care who says pounds is a unit of mass, they are wrong! If you
use pounds in a formula that wants mass, your answer will be WRONG.


please read the NIST publications which define the Avoirdupois pound in
terms of kilograms. this is not debateable since NIST is *the* authority in
the US.

Gravity

--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com

gravity wrote:

please read the NIST publications which define the Avoirdupois pound in
terms of kilograms. this is not debateable since NIST is *the* authority in
the US.

The NIST publications define the numeric conversion factors, not the
legality for use of any particular terminology.

The approximate conversion factor for a pound (mass) is 0.4535924 kilogram.

The approximate conversion for a pound (force) is 4.448222 newton.

The gravitational acceleration, small g, is defined as exactly 9.80665
in SI units, but it is not similarly defined in inch/pound units.

Interestingly enough, however, is that the ratio of pound-force per
pound (lbf/lb) (thrust to mass ratio) is exactly converted to newton per
kilogram (N/kg) by the factor 9.80665.

The position of the US Government can be summarized from the following
excerpt found in Federal Standard 376B, Preferred Metric Units for
General Use by the Federal Government.

In the intro to the section on mass there is a note that says,

*** There is ambiguity in the use of the term "weight" to mean either
force or mass. In general usage, the term "weight" nearly always means
mass and this is the meaning given the term in U.S. laws and
regulations. Where the term is so used, weight is expressed in kilograms
in SI. In many fields of science and technology the term "weight" is
defined as the force of gravity acting on an object, i.e., as the
product of the mass of the object and the local acceleration of gravity.
Where weight is so defined, it is expressed in newtons in SI. ***

The document then goes on to show many conversion factors from both
pounds (mass) and pounds (force) to SI units. No indication that one is
more legal or correct than the other.

Soooo, use pounds any way you wish; just do the math correctly.

73,
Gene
W4SZ

gravity wrote:


please read the NIST publications which define the Avoirdupois pound in
terms of kilograms. this is not debateable since NIST is *the* authority in
the US.

The NIST isn't the authority on the laws of physics. One of the most
basic of which is F=MA, if you use pounds for mass in that formula you
get the wrong answer. Nothing that NIST says will change that.

200 lbs = 6.25 slugs * 32 ft/sec^2. Using pounds, the formula won't
work any other way.

--
Chris W
KE5GIX

Gift Giving Made Easy
Get the gifts you want &
give the gifts they want
One stop wish list for any gift,
from anywhere, for any occasion!
http://thewishzone.com

Chris W wrote:
gravity wrote:


please read the NIST publications which define the Avoirdupois pound in
terms of kilograms. this is not debateable since NIST is *the* authority in
the US.

The NIST isn't the authority on the laws of physics. One of the most
basic of which is F=MA, if you use pounds for mass in that formula you
get the wrong answer. Nothing that NIST says will change that.

200 lbs = 6.25 slugs * 32 ft/sec^2. Using pounds, the formula won't
work any other way.

Bull****.

Here are a couple of other ways that work just fine with FFU:

200 lb * 32.2 ft/s² = 6440 pdl

0.52 slinch * 386 in/s² = 200 lbf

Be sure to distinguish pounds force (lbf) from pounds (lb), and units
of measure should remain unchanged in the plural, without adding any
language-specific "s" or whatever.

Gene Nygaard