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# How else than by comparison

## How else than by comparison - Physics Forum

### How else than by comparison - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

#1
01-15-2006, 05:43 PM
 Don1 Guest Posts: n/a
How else than by comparison

How else than by comparison with a known mass, can we weigh a gram, or
a kilo?

Don

#2
01-15-2006, 05:50 PM
 Sam Wormley Guest Posts: n/a
How else than by comparison

Don1 wrote:

o spring scale
o monitor orbits
o F = ma, where F and a are measured

#3
01-15-2006, 06:52 PM
 odin Guest Posts: n/a
How else than by comparison

> How else than by comparison with a known mass, can we weigh a gram, or

Of all the questions and comments I have seen you make, this is the first
good one I ever saw from you Don1. A bit like what you would get from a
clever grade six student. But at least it is valid and makes sense.

The answer is that to "weigh" an object you do indeed need to compare it
directly or indirectly (virtually always indirectly in practice) with a
"known weight". This is what calibration is all about. The word "weigh" is
street-talk. In physics-talk, one does not "weigh" an object. Rather, one
determines the mass of the object. And we don't refer to the standard of
comparison as a "standard weight", but rather as a "standard mass".

If you measure mass using a balance scale, you are comparing against a known
mass, which if it has any legitimacy, originated through a chain of
comparisons back to the standard mass.

If you measure mass using a spring scale, you are comparing against a known
force, which if it has any legitimacy, originated through a chain of
comparisons back to the force of the standard mass in a standard
gravitational acceleration.

Any other method that I can think of would be some variation of the above
two cases, where comparing masses or comparing forces is used. In either
case, the standard is used to calibrate the measurement setup. Without a
standard, the measurement is meaningless, as you are working without units.
What would you make of it if I told you that I was 1776 tall? Without out
the units being supplied, this tells you nothing. On the other hand, by
defining my own funky units, I can make the statement true.

#4
01-15-2006, 06:55 PM
 N:dlzc D:aol T:com \(dlzc\) Guest Posts: n/a
How else than by comparison

Dear Sam Wormley:

"Sam Wormley" <[Only registered users see links. ]> wrote in message
news:xXvyf.707045\$_o.93381@attbi_s71...
o mass spectrometer (which is a lot like "monitor orbits"

David A. Smith

#5
01-16-2006, 12:46 PM
 Don1 Guest Posts: n/a
How else than by comparison

Sam Wormley wrote:

I think that I'm looking for something more basic; like who designed
those scale devices, and decided what numbers to use, and where to put
them.

Presently such measuring instruments are calibrated with metric units:
All the yeggs are in the same basket.

The original designers knew little if anything about metric units.

Who concocted the combination, and came up with the menu that 1 dyne
exerted for 1 sec; is the impulse that will displace a 1 gram body at a
rate of 1 centimeter per sec^2?

#6
01-16-2006, 12:51 PM
 Don1 Guest Posts: n/a
How else than by comparison

odin wrote:

You are still the same BS artist that always were.

#7
01-16-2006, 05:22 PM
 Clemens W Guest Posts: n/a
How else than by comparison

Don, still a clueless twit, wrote:

You didn't change either, Don.

A. Friend

#8
01-16-2006, 07:51 PM
 Don1 Guest Posts: n/a
How else than by comparison

Clemens W wrote:

#9
01-17-2006, 02:44 PM
 Andy Resnick Guest Posts: n/a
How else than by comparison

Sam Wormley wrote:

Actually, Don finally makes a valid point here. And I should also point
out that forces are not measurable, in the way that displacement is
measureable. There's no such thing as a 'force-o-meter'. This is (part
of) the fundamental deficiency in Newtonian mechanics.

But, there is a research program to replace the standard kilogram with
an electronic equivalent, see for example:

[Only registered users see links. ]

[Only registered users see links. ]

--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
#10
01-17-2006, 03:20 PM
 jimp@specsol.spam.sux.com Guest Posts: n/a
How else than by comparison

In sci.physics Andy Resnick <[Only registered users see links. ].edu> wrote:

Strain gauge?

--
Jim Pennino

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