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Tire Pressure increases 5 lbs in one ride

Old 05-31-22, 10:08 AM
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Originally Posted by cyccommute
Nope. At -50°F (227K), the pressure would be 30 psi. The tires might go flat because the rubber isn’t flexible anymore and may crack but the pressure wouldn’t be zero. You’d need to condense the air to get to near zero pressure which is -320°F (196°C). The rubber will definitely shatter at that temperature. But notice that the pressure change is only 10 psi.

I’ve done demonstrations with balloons in liquid nitrogen where I can show liquid air (and zero pressure in the balloon). It’s very cool to watch the balloon collapse and a pool of liquid form in the bottom. It’s also very cool to watch the balloon expand as the liquid air boils off.
I didn't say the pressure would be zero, did I? Admit that, first off.

I'm not sure what you're contradicting with your "Nope.", but it's offensive, either way. Are you one of those posters who always has to be right?
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Old 05-31-22, 10:16 AM
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Originally Posted by Fredo76
I didn't say the pressure would be zero, did I? Admit that, first off.
You said the tire would be “flat”. That implies zero pressure. I don’t go out and look at a tire that is low and say it is “flat”. It may be going flat but it isn’t flat yet. A 10psi pressure drop due to temperature isn’t even close to being “flat”. It may be low but it isn’t “flat”.

I'm not sure what you're contradicting with your "Nope.", but it's offensive, either way.
I’m contradicting your assertion that the tire is flat. The rest of the post relates back to that assertion. It’s not an “offense”. It’s just a introduction to the rest of the post. “Nope” and “no” are equivalent statements
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Old 05-31-22, 10:46 AM
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Do we have an IGNORE feature? How-to, please.

Originally Posted by cyccommute
You said the tire would be “flat”. That implies zero pressure. I don’t go out and look at a tire that is low and say it is “flat”. It may be going flat but it isn’t flat yet. A 10psi pressure drop due to temperature isn’t even close to being “flat”. It may be low but it isn’t “flat”.



I’m contradicting your assertion that the tire is flat. The rest of the post relates back to that assertion. It’s not an “offense”. It’s just a introduction to the rest of the post. “Nope” and “no” are equivalent statements
Your first two sentences above, taken together, constitute ********. I'd tell you more about my lived experience regarding tires at -50 degrees, but that would just be more ammo for your **** cannon. You ARE one of those posters who always has to be right.
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Old 05-31-22, 11:35 AM
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Originally Posted by Fredo76
Your first two sentences above, taken together, constitute ********. I'd tell you more about my lived experience regarding tires at -50 degrees, but that would just be more ammo for your **** cannon. You ARE one of those posters who always has to be right.
Yes. We have an ignore function. I’m sure you can find it somewhere.

We also have rules against profanity…even stuff that is “starred” out.

Please tell me how my first two sentences above…taken together or separately…constitute bovine excrement (that’s how you do profanity). Did you change the tire at -50°F because it was “flat” or did you just drive along on a low(er) pressure tire? Of course, the pressure is lower. Is the tire “flat”…i.e zero pressure? Obviously not.
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Old 05-31-22, 12:41 PM
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Originally Posted by cyccommute
Partly but it’s mostly because the “gauge” part in psig is calibrated for sea level pressure.
No.

A tire pressure gauge is not calibrated to be zero at sea level atmospheric pressure. It is calibrated for zero when the pressure on the inside of the tire is equal to the pressure outside the tire (atmospheric pressure). That could be at sea level or at 20,000 feet. A flat tire reads zero in either situation.

All tire pressure gauges are designed to read the pressure inside the tire ABOVE the actual atmospheric pressure. This is why measured pressure in a tire increase with altitude, even thought the absolute pressure does not. The pressure in the tire remains the same, but the atmospheric pressure drops. Thus the difference increases, thus the tire measures (and behaves) higher in pressure.

For a simple explanation, read the 4th and 5th paragraphs: https://www.tirerack.com/tires/tiret...jsp?techid=167

You can do all the gas law calculation you want, but it does not change the fact of what tire gauges are actually measuring.
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Old 05-31-22, 02:55 PM
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Originally Posted by cyccommute
and Avogadro’s Law (V/n=k), where n is the number of particles of gas).
"n" is the number of moles of particles... I'm sure you'll understand why I had to correct that.

Originally Posted by cyccommute
A psia gauge measures the pressure in the vessel compared to a vacuum while a psig gauge measures the pressure compared to a standard atmospheric pressure.
All gauges measure relative pressure. Absolute gauges measure relative pressure and then use a trick or adjustment to convert it to absolute.

Originally Posted by cyccommute
Partly but it’s mostly because the “gauge” part in psig is calibrated for sea level pressure.
Yeah that's hooey... a gauge calibrated for sea level pressure would read actual 0 psig as a negative value at altitude.
Sea level pressure comes in handy when doing volumetric conversions to STP.
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Old 05-31-22, 03:21 PM
  #57  
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Originally Posted by 2manybikes
How long is a rope?
I don't know, but I've about reached the end of mine!
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Old 05-31-22, 03:33 PM
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Originally Posted by 2manybikes
How long is a rope?

it's many strands.
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Old 05-31-22, 03:53 PM
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Originally Posted by DiabloScott
"n" is the number of moles of particles... I'm sure you'll understand why I had to correct that.
The term “moles” is a description of the number of molecules. A “mole” is defined as 6.02 x 10^23 particles of a substance. The number of particles can be a fraction of a mole or a multiple of a mole. To say the number of particles is the same as saying the number of moles. To say “the number of moles of particles” is redundant.

All gauges measure relative pressure. Absolute gauges measure relative pressure and then use a trick or adjustment to convert it to absolute.
A Bourdon tube gauge is a closed, flattened copper tube that tries to straighten out when pressure is applied to the tube by some system. An absolute gauge is zeroed against a vacuum (with a little bit of calculation because you can’t get a perfect vacuum) while a “gauge” pressure gauge is zeroed at atmospheric pressure. A gear system is connected to the dial to serve as an indicator. The actual calibration is done with a dead weight system or some kind of digital reference gauge but both are adjusted for standard pressure. You could build the gauge at any altitude but it is calibrated against sea level pressure.

Other pressure gauges use springs and cylinders for the measurement but they are still calibrated against sea level (usually poorly).

Yeah that's hooey... a gauge calibrated for sea level pressure would read actual 0 psig as a negative value at altitude.
Sea level pressure comes in handy when doing volumetric conversions to STP.
I’ve used a whole lot of pressure gauges in my many years of doing chemistry above 5000 feet (5800 feet, actually). The dial measures zero…not below zero…zero. The bit over 2 psi difference between sea level and the altitude at my lab is usually of such a small difference that there is no need to report the difference (2 psi out of 100 or 1000) because it doesn’t matter all that much.For some things we would report the pressure difference or make adjustments to STP but more often than not, it won’t make a difference.

I read Kapusta’s statement as a change in pressure of a filled vessel with altitude. That would depend on the vessel. A cylinder of gas filled at sea level is going to have the same pressure at altitude as at sea level. A tire filled at sea level and taken to altitude might show a slight change in pressure but that is because the “vessel” in that case is elastic. That is going to complicate the problem because the tire expands (slightly) which would result in a decrease in pressure (Boyles’ Law).
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Old 05-31-22, 04:50 PM
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Originally Posted by Kapusta
No.
Yes.

A tire pressure gauge is not calibrated to be zero at sea level atmospheric pressure. It is calibrated for zero when the pressure on the inside of the tire is equal to the pressure outside the tire (atmospheric pressure). That could be at sea level or at 20,000 feet. A flat tire reads zero in either situation.
Pressure gauges are calibrated to read zero at sea level. “Gauge” in psig means standard pressure. Yes, it will read zero at any altitude but it is calibrated to read zero at sea level. We use it as a differential but it is designed to read compared to sea level.

By the way, thank you for saying that “flat” means zero pressure.

All tire pressure gauges are designed to read the pressure inside the tire ABOVE the actual atmospheric pressure. This is why measured pressure in a tire increase with altitude, even thought the absolute pressure does not. The pressure in the tire remains the same, but the atmospheric pressure drops. Thus the difference increases, thus the tire measures (and behaves) higher in pressure.
It’s more complicated than just due to an increase in altitude, especially where tires are concerned. A tire is at least partly elastic. The pressure differential between altitudes is most likely to be due to that elastic nature than any change in external pressure. A rigid metal cyclinder will not measure a decrease in pressure with a change in altitude because the cylinder is rigid. A tire expands slightly which means that the volume increases. Increased volume with the same amount of gas will cause the pressure to decrease.

For a simple explanation, read the 4th and 5th paragraphs: https://www.tirerack.com/tires/tiret...jsp?techid=167
They aren’t taking into account the decrease in pressure on the outside of the elastic tire, however. That could easily account for the pressure difference. It’s not a simple problem.
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Old 05-31-22, 05:47 PM
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Originally Posted by cyccommute
The term “moles” is a description of the number of molecules. A “mole” is defined as 6.02 x 10^23 particles of a substance. The number of particles can be a fraction of a mole or a multiple of a mole. To say the number of particles is the same as saying the number of moles. To say “the number of moles of particles” is redundant.
Not redundant. 5 dozen eggs is not the same as 5 eggs, and n moles of particles is not the same as n particles. You're trying to find a loophole to save your error - I advise capitulation.

Originally Posted by cyccommute
A Bourdon tube gauge is a closed, flattened copper tube that tries to straighten out when pressure is applied to the tube by some system. An absolute gauge is zeroed against a vacuum (with a little bit of calculation because you can’t get a perfect vacuum) while a “gauge” pressure gauge is zeroed at atmospheric pressure. A gear system is connected to the dial to serve as an indicator. The actual calibration is done with a dead weight system or some kind of digital reference gauge but both are adjusted for standard pressure. You could build the gauge at any altitude but it is calibrated against sea level pressure.
Bourdon tube gauges are less susceptible to ambient pressures, but not immune - and I've never seen a Bourdon tube gauge that reads psia... show me one and I'll eat my comment. Most Pabs gauges are for use in highly sensitive lab instruments and use a reference chamber that is not susceptible to atmospheric fluctuations. This has nothing to do with bike tires of course.




Originally Posted by cyccommute
I’ve used a whole lot of pressure gauges in my many years of doing chemistry above 5000 feet (5800 feet, actually). The dial measures zero…not below zero…zero.
Me too, doing mechanical engineering. I've also used them at XXXX feet below sea level (confidential information). Do your gauges have a pin that keeps the dial from going below zero?

This is fun bickering - but defining mole and bourdon tube to an engineer is condescending... (that means talking to people like they're stupid).
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Old 05-31-22, 06:03 PM
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Originally Posted by rbrides
same gauge before and after. The Topeak digital gauge.
What was your starting psi? I have the same tires/size and a Topeak gauge. It's not unusual to get a 25-30° change here.
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Old 05-31-22, 08:28 PM
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Originally Posted by cyccommute
Yes.



Pressure gauges are calibrated to read zero at sea level. “Gauge” in psig means standard pressure. Yes, it will read zero at any altitude but it is calibrated to read zero at sea level. We use it as a differential but it is designed to read compared to sea level.

By the way, thank you for saying that “flat” means zero pressure.



It’s more complicated than just due to an increase in altitude, especially where tires are concerned. A tire is at least partly elastic. The pressure differential between altitudes is most likely to be due to that elastic nature than any change in external pressure. A rigid metal cyclinder will not measure a decrease in pressure with a change in altitude because the cylinder is rigid. A tire expands slightly which means that the volume increases. Increased volume with the same amount of gas will cause the pressure to decrease.



They aren’t taking into account the decrease in pressure on the outside of the elastic tire, however. That could easily account for the pressure difference. It’s not a simple problem.
Yes, it is actually that simple. And that is why the measured pressure increases with altitude. The same phenomenon (measured pressure increasing with altitude) would also occur with a metal canister. In fact, is DOES happen with air forks and shocks (though the real world effect is negligible due the the high pressures they run).

Tire pressure gauges measure the pressure difference between the the inside of the tire and surrounding atmospheric pressure. This is incredibly basic stuff and anyone with the most basic understanding of how a simple tire pressure gauge works knows this. They are not calibrated to "sea level" that does not even make sense to say.

In fact, I am fairly certain that you know this as well. You are clearly a smart guy. Unfortunately for reasons that nobody but you can understand, you decided to disagree for the sake of argument, and are now trying to defend a nonsensical point by changing the subject and making arguments that do not even relate to the topic.

I don't know why you dig yourself into these holes, but it gets old.

Oh, and I did NOT say that there was zero pressure in a flat tire. I said that a tire pressure gauge would READ zero (because the pressure inside and outside the flat tire is the same). But I think you actually know this already. You’re just trying to confuse things.

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Old 06-01-22, 06:56 AM
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Originally Posted by cyccommute
The term “moles” is a description of the number of molecules. A “mole” is defined as 6.02 x 10^23 particles of a substance. The number of particles can be a fraction of a mole or a multiple of a mole. To say the number of particles is the same as saying the number of moles. To say “the number of moles of particles” is redundant.
No, actually, "particles" is the superset of "molecules" when you're showing off Avogadro's number, because it's also possible to have a mole of atoms (whether gaseous or solid). You know that, of course. So can we lay this tedious argument for the sake of argument to the side for a while, please?
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Old 06-01-22, 07:17 AM
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Originally Posted by DiabloScott
Not redundant. 5 dozen eggs is not the same as 5 eggs, and n moles of particles is not the same as n particles. You're trying to find a loophole to save your error - I advise capitulation.
I used number of particles to simplify my statement. No 5 dozen eggs isn’t the same as 5 eggs but it is the same as 60 eggs. Saying you have 6.02 x 10^23 particles is the same as saying that you have n moles. Most people don’t know the concept of “mole” so saying “number of particles” is just as valid. I made no error.

Bourdon tube gauges are less susceptible to ambient pressures, but not immune - and I've never seen a Bourdon tube gauge that reads psia... show me one and I'll eat my comment. Most Pabs gauges are for use in highly sensitive lab instruments and use a reference chamber that is not susceptible to atmospheric fluctuations. This has nothing to do with bike tires of course.
You mean like like this one?



Me too, doing mechanical engineering. I've also used them at XXXX feet below sea level (confidential information). Do your gauges have a pin that keeps the dial from going below zero?
Some do have a pin and some don’t. I’ve used gauges on vessels that I’ve had to apply a vacuum to prior to a procedure and the gauge showed negative pressure. At rest, the gauge showed no inclination to be below zero, however. Most of the gauges have a fairly large range of pressure…some up to thousands of psi so a 2 psi difference isn’t going to move the needle.

This is fun bickering - but defining mole and bourdon tube to an engineer is condescending... (that means talking to people like they're stupid).
I have no idea who you are or what you do. 99.9% of the population has only had a passing exposure to the concept of a mole with the vast majority of those never having had any exposure. A larger percentage have no idea what a bourdon tube is.

My redefining a mole to you was to point out you are in error about the concept. “n” in the ideal gas law is the number of moles. But, because the number of particles is equivalent to the number of moles, “particles” can be substituted for moles. Of course, the units on the gas constant would have to be changed in a calculation. “Moles” is a short hand that is easier to deal with but stating the number of particles is correct.

From a historical context, Avogadro’s Law states the “amount of gas”. Avogadro develop his law in 1812 but the Avogadro’s number (6.02 x10^23 particles) wasn’t established until 1909. The Ideal Gas Law was described in 1834. The concept of a “mole” wasn’t described until 1900. People used other units prior to the discovery of the mole and Avogadro’s number. We just use the mole as short hand.
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Old 06-01-22, 07:20 AM
  #66  
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How bout them digital pressure gauges. Don't the transducer sense tire pressure independently from atmosphere? I use a digital one. Tospeak or something. I don't like how it attaches to the valve stem but otherwise it is rock solid repeatable.

I measured pressure before yesterday's ride, it was 80 psi at 72F. It got to 98F on my Garmin during my ride, the BMW said 100F. I should have written down my numbers but I was so hot and tired, I forgot. But I seem to recall confirming that tire pressure rises with temperature and my tires were more than 100F. Getting old and cranky with poor eyes and memory has its limitations.
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Old 06-01-22, 07:29 AM
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Originally Posted by pdlamb
No, actually, "particles" is the superset of "molecules" when you're showing off Avogadro's number, because it's also possible to have a mole of atoms (whether gaseous or solid). You know that, of course. So can we lay this tedious argument for the sake of argument to the side for a while, please?
A “molecule” or an atom or a basketball or an electron is a “particle”, is it not? It’s possible to have a mole of anything. A mole is just a count of particles of any kind. It is not incorrect to use “mole” and “number of particles” interchangeably. For that matter it is not incorrect to use “mole” and “grams of substance” interchangeably. The mole was originally defined in terms of mass.

To be clear, I was not the one who drug the discussion off into the weeds. I pointed out that the Ideal Gas Law is a poor tool for calculating the effect that temperature has on pressure.

Nor did I say that temperature has no influence on pressure. It does. rbrides’ increase in pressure could be related to a temperature increase but it also could be related to a reading error or some combination of the two.
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Old 06-01-22, 07:55 AM
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Originally Posted by cyccommute
I read Kapusta’s statement as a change in pressure of a filled vessel with altitude. That would depend on the vessel. A cylinder of gas filled at sea level is going to have the same pressure at altitude as at sea level. A tire filled at sea level and taken to altitude might show a slight change in pressure but that is because the “vessel” in that case is elastic. That is going to complicate the problem because the tire expands (slightly) which would result in a decrease in pressure (Boyles’ Law).
Well then you read it wrong because this is NOT what I said. I never said the true air pressure in the tire or vessel changes. I said the READING OF THE TIRE GAUGE changes because what it is reading is the difference between the pressure in the tires (or whatever vessel) and the atmospheric pressure. As altitude increases, atmospheric pressure decreases and the difference in pressures increases, thus the reading of the tire gauge increases.

If you are going to argue with me, at least argue with what I am actually saying.
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Old 06-01-22, 08:00 AM
  #69  
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Originally Posted by cyccommute
A mole is just a count of particles of any kind. It is not incorrect to use “mole” and “number of particles” interchangeably. For that matter it is not incorrect to use “mole” and “grams of substance” interchangeably. The mole was originally defined in terms of mass.
You should be glad you weren't in my class or lab -- you'd have a zero for the day. You forgot the factors that scale between mole and number of particles or grams, and you were sloppy with using mass.
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Old 06-01-22, 08:20 AM
  #70  
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The reason I am careful about pressure on tubeless tires goes back to 2016 when my Compass tubeless tires blew off 15 psi under the labeled max pressure and the recent podcast where Silca's Josh Poertner said he had tires blow off at 80 psi that I believe would be rated for 75 psi. I am just an old mediocre engineer who doesn't really want to get into the technical side of this matter, but I believe 100% what Josh said because I observed a similar blow off. (Yes, I reported it to the seller)

Personally, I would run a 30-32mm wide hookless at lower pressure but not 25mm at required pressure (75 psi) and maybe not even 28 mm unless I was really confident in my guage or I lost some weight.
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Old 06-01-22, 12:27 PM
  #71  
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My Topeak Smart gauge measures at half pound increments. 80.5 front and 80 rear psi at 50°. Starting temp was about 70° for 25 miles on blacktop. Temp gauge read over 90, but it was more like 85. The tires came in at 82 psi. Not the 5 pound increase, but temperatures did increase. Not worth worrying about.



Good reason to go for a ride on a nice day.
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Old 06-01-22, 12:50 PM
  #72  
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My blood pressure increases in one ride.
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Old 06-01-22, 03:04 PM
  #73  
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Originally Posted by cyccommute
Saying you have 6.02 x 10^23 particles is the same as saying that you have n moles. Most people don’t know the concept of “mole” so saying “number of particles” is just as valid. I made no error.
No, it's the same as saying you have ONE mole. The point is, if you put the "number" of particles in the ideal gas law like you suggested, you'd get the wrong answer... ie an error.

Originally Posted by cyccommute
You mean like like this one?
Dead link... is that a joke?

Originally Posted by cyccommute
99.9% of the population has only had a passing exposure to the concept of a mole with the vast majority of those never having had any exposure.
You just made up that statistic, right? I understand exaggerating for effect, but something like 3% of US Citizens have STEM degrees, and we're talking about a high school science concept.

Also, your sentence doesn't even make sense... the vast majority of people with a passing exposure have never had any exposure?

Originally Posted by cyccommute
My redefining a mole to you was to point out you are in error about the concept. “n” in the ideal gas law is the number of moles. But, because the number of particles is equivalent to the number of moles, “particles” can be substituted for moles. Of course, the units on the gas constant would have to be changed in a calculation.
This is incorrect and you know it. A mole is a number of items; just like a dozen, or a score, or a gross. A mole is an Avogadro's number of something. One mole is not one particle - you are off by 23 orders of magnitude. We both understand this and you're still trying to cover up your misstatement.

I have no idea who you are or what you do.
Well you seem to have concluded that I don't know what I'm talking about. Science people understand what you meant with your sloppy narrative. You and I are not arguing science though, we're arguing language. For reference, I have to explain technical concepts to non-technical people, in peer-reviewed reports - so my attention to correct usage of terminology and proper sentence construction is a skill I've been polishing for a long time.
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Old 06-01-22, 06:29 PM
  #74  
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Well, I'd say something, but this comes to mind...ultracrepidarian.
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Old 06-04-22, 07:40 AM
  #75  
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Originally Posted by curbtender
Well, I'd say something, but this comes to mind...ultracrepidarian.
Thanks! I learned a (handy!) new word.
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