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Re: [Phys-l] force or mass



"... Some contexts ..."!


Officially the lb or # refers to mass.



"A number of different definitions have been used, the most common today being the international avoirdupois pound of exactly 0.45359237 kilogram."

Wikipedia:

http://en.wikipedia.org/wiki/Pound_(mass)#Avoirdupois_pound



Unless the above refers to kg-f, pound appears to be a mass.



From the NIST HdBh:



"The pull of gravity on the earth gives an object a downward acceleration of about 9.8 m/s2. In trade and commerce and everyday use, the term "weight" is often used as a synonym for "mass." The "net mass" or "net weight" declared on a label indicates that the package contains a specific amount of commodity exclusive of wrapping materials. The use of the term "mass" is predominant throughout the world, and is becoming increasingly common in the United States. (Added 1993)"

The next paragraph:


W. Use of the Terms "Mass" and "Weight." [NOTE 1, See page 6]
When used in this handbook, the term "weight" means "mass." The term "weight" appears when inch-pound units are cited, or when both inch- pound and SI units are included in a requirement. The terms "mass" or "masses" are used when only SI units are cited in a requirement. The following note appears where the term "weight" is first used in a law or regulation.
NOTE 1: When used in this law (or regulation), the term "weight" means "mass." (See paragraph V. and W. in Section I., Introduction, of NIST Handbook 130 for an explanation of these terms.) (Added 1993) 6"


The exception is torque units.

bc, "sticking to his guns".

p.s. of course, this has been mainly ATA, much decried by JD, OTOH, if the US govt. (all powerful) claims a # is a measure of mass then it is; nicht wahr?

p.s. NBS definition of the pound:

http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf

Finally?, all this will soon? be obsolete; already my tyre gauge includes Pa (kPa).


On 2008, Nov 05, , at 15:34, Richard Tarara wrote:

From the referenced site:

In some contexts, the term "pound" is used almost exclusively to refer to
the unit of force and not the unit of mass. In those applications, the
preferred unit of mass is the slug, i.e. lbf·s²/ft. In other contexts, the
unit "pound" refers to a unit of mass. In circumstances where there may
otherwise be ambiguity, the symbols "lbf" and "lbm" and the terms
"pounds-force" and "pounds-mass" can be used to distinguish.

So may I suggest that Bernard read the whole article! ;-)

Rick


----- Original Message -----
From: "Bernard Cleyet" <bernardcleyet@redshift.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Wednesday, November 05, 2008 3:47 PM
Subject: Re: [Phys-l] STUDY SUGGESTS NO CHILD LAW MAY BE DUMBING
DOWNSTUDENTS


"The pound-force is approximately equal to the gravitational force
exerted on a mass of one avoirdupois pound on the surface of Earth."

From your reference.



And my reference:



"This article is about the unit of mass. For the unit of force, see
Pound-force.
The pound or pound-mass (abbreviation: lb, lbm, or sometimes in the
United States: #) is a unit of mass used in the imperial, United
States customary and other systems of measurement."



bc suggests Robert read more carefully, and is reminded of Einstein's
dictum: change the facts to fit the theory.

On 2008, Nov 04, , at 23:56, Robert Yeend wrote:

Well, Wiki also disagrees with you

http://en.wikipedia.org/wiki/Pound-force

Bob

On Nov 4, 2008, at 10:43 PM, Bernard Cleyet wrote:

I, too, went thru life (about > 50 years) thinking the pound was a
unit of force. It is not, as pointed out by JD recently.

https://carnot.physics.buffalo.edu/archives/1999/10_1999/
msg00645.html

"For what it's worth" Wiki. agrees w/ me also:

http://en.wikipedia.org/wiki/Pound-mass

bc, disabused.



On 2008, Nov 04, , at 10:25, Rick Tarara wrote:

The technically
incorrect 2.2 lbs = 1 kg (formally the weight of 1 kg is 2.2 lbs)
works
fine.

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Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l