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UK back to "imperial" measurements ?
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vk6zgo:

--- Quote from: bd139 on June 05, 2022, 09:55:36 pm ---
--- Quote from: TimFox on June 05, 2022, 09:50:49 pm ---
--- Quote from: bd139 on June 05, 2022, 09:48:45 pm ---Kg was never used as a force. Force is N (newtons)

--- End quote ---

You have never seen a pressure gauge calibrated in kg/cm2 or kgf/cm2?
Do they only export those gauges to the US?

--- End quote ---

That’s a pressure not a force. And it should be pascals.

--- End quote ---

As it is in Oz!
IanB:

--- Quote from: TimFox on June 06, 2022, 01:02:24 am ---Re:  IanB
Your discussion about the difference between a "pound mass" and "pound force" is consistent with my discussion of using lb av at the grocery store to weigh food.
However, here is an example of my reasoning not to use lbm:
Imagine a spacecraft whose mass is 100 lbm.  We then apply a force of, say, 10 lbf to accelerate it in a desired direction.
Applying Newton's second law straight out of the bottle, F = m A will give the wrong result, unless we throw another factor gN, the defined standard acceleration of gravity.
In careful US usage, one should use pounds of force and slugs of mass, just as in careful metric usage one uses Newtons of force and kg of mass.

I remember in high-school physics class (11th grade), an important initial hurdle for the students was to understand the difference between mass and weight.  The instruction was in both customary and metric units, and I learned some important factors for mental calculation, such as 88 ft/sec = 60 mph (exactly).

--- End quote ---

Indeed. Lecture 1, day 1 of my engineering degree was introducing the subject of units of measure, and the correct use thereof.

Until that point, my high school curriculum had been taught exclusively in SI units. Imagine our surprise when this conversion factor gc started appearing in all sorts of equations, and how important it was to remember it when venturing off the SI island.

Here is the famous Bernoulli equation as described in a standard industry reference:



We may observe how the mysterious factor "g" appears in some terms. And what the heck is that 144 doing there?  ???

Furthermore, what about that "foot pounds per pound" as unit of measure for head (loss)? Why don't the pounds cancel out to leave just feet? (Actually, they do, if you are a practicing engineer and you know what's going on.) The equivalent SI unit would be J/kg, and maybe that is equivalent to meters? (Yes, it is, as long as you remember the gc conversion factor when going from one to the other. See? You can't escape gc even in SI units  ;D )
IanB:

--- Quote from: TimFox on June 05, 2022, 09:50:00 pm ---Specifically:  when the local consumer-department inspector checks the setting on a sales scale, he places a known artifact on the scale to check the reading.  The marking on that calibration mass assumes a standard gravitational acceleration value (roughly that at sea level at 45o latitude) to know the actual weight at that standard location.  (NIST considers that acceleration value to be a defined constant, like 1 in = 2.54 cm exactly.)
However, he will use the same set of reference weights in Denver as in New York, even though a pound of steak transported to Denver weighs less at high altitude.
--- End quote ---

I realized afterwards, that this was in fact a statement designed to lead readers into a trap.

If a set of scales in New York is calibrated with a standard 1 kg weight, then when the scale reads 1 kg you will have 1 kg mass of your desired commodity on the scale.

If a different set of scales in Denver is calibrated with a standard 1 kg weight, then when the scale reads 1 kg you will also have 1 kg mass of your desired commodity on the scale. Any difference in local gravity is canceled out by the calibration.

Now, if you calibrated the scale in New York, and then transported the scale (not the steak) to Denver, then you might have a problem. But that was not the premise.

The key point here is that a 1 kg calibration weight has a mass of 1 kg, and that mass will remain the same everywhere in the world. If you use it to calibrate a scale, then the scale will read mass accurately at the location where calibrated.
TimFox:

--- Quote from: themadhippy on June 06, 2022, 01:19:58 am ---
--- Quote ---If we look to a regulatory source, namely "NIST Handbook 130: Uniform Laws and Regulations in the areas of legal metrology and fuel quality (2022)"
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But only applicable to america,if i was served 0.473177 liters in my liquid pint glass id be questioning the parentage of the bartender

--- End quote ---

Why would your bartender serve you a US pint in the UK?
themadhippy:

--- Quote ---Why would your bartender serve you a US pint in the UK?
--- End quote ---
because some one has told them the above book is regulatory  without adding "only in the usa" .
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