Why does the Dry Air Gas Constant vary?

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Discussion Overview

The discussion centers on the variation in the dry air gas constant, with participants exploring the different values reported by various sources and questioning the reasons behind these discrepancies. The scope includes conceptual understanding and technical reasoning related to the measurement and calculation of the gas constant.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant notes several different values for the dry air gas constant from various sources, expressing confusion about the reasons for these differences.
  • Another participant suggests that the differences are negligible when rounded to three significant figures and emphasizes the importance of checking the methods and dates of the measurements.
  • A participant questions whether the variations are truly insignificant and suggests that there should be a means to obtain an exact value for the gas constant at specific locations, acknowledging the potential challenges in doing so.
  • A participant provides a calculation using the universal gas constant and the molecular weight of dry air to derive a specific value for the gas constant.
  • One participant expresses satisfaction with the discussion, indicating they have resolved their confusion.
  • Another participant uses an analogy about measuring a kitchen table to argue that while the gas constant may not be exact, it should not hinder practical applications, suggesting that three significant figures may be sufficient for calculations.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the variations in the gas constant values. While some suggest the differences are minor, others argue for the importance of precision and the need for exact measurements, indicating that the discussion remains unresolved regarding the implications of these variations.

Contextual Notes

Participants reference different sources and methods for obtaining the gas constant, highlighting potential variations due to measurement techniques and the date of data collection. There is an acknowledgment of the challenges in achieving an exact value for the gas constant.

Who May Find This Useful

This discussion may be useful for individuals interested in thermodynamics, atmospheric science, or those exploring the implications of gas constants in practical applications.

Robert James Liguori
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I'm confused on why the dry air gas constant varies:
Can someone please explain why it differs and how it is constructed. Thanks, Robert

Reference:
[link to personal website removed]
 
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to within 3 significant figures these are all the same !
It would be worth checking how each source obtained the value, especially the date when the values were measured.
Methods vary and improve over the years
 
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I am not a physicist... so you are implying that the differences in the values is insignificant? To me, it should be exact... or a means should be in place to get the exact value at each given location of sampling... if this was indeed possible, which it may not be. Please advise.
 
universal gas constant = 8314.32 (in 1976 Standard Atmosphere)
molecular weight of dry air = 28.964

8.3143 / 28.964 = 0.28705634580859 (e.g., 287.056)
 
I figured it out... thanks for your help.

[link to personal website removed]
 
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Can you measure the length of your kitchen table exactly? Why not? Are you going to let that keep you from buying a tablecloth?

Even if the value of the gas constant is not exact, does that bring your calculations to a screeching halt (until you find the exact value, which doesn't exist)? Isn't 3 significant figures accurate enough for you?
 
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On these words of wisdom, the OP's question has been answered. Thread closed.
 

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