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Myth #1: The Maxwellian Velocity Distribution can be measured directly with a flux of a model gas.

In many physics laboratories in schools and universities, the experiment "Maxwellian Velocity Distribution" can be found with a model gas of spheres and measuring the velocity distribution at a flux of the model gas:

REALITY:

The ensemble of the model gas has (nearly) a Maxwellian Velocity Distribution

const₁ *v² *e^{const₂ *v2} .

But only the flux of the pushed out balls is being measured in this experiment, not the ensemble!

Because a physical flux is, by definition, the integral over the density times velocity (v) normal to the cross section, the velocity distribution of the pushed out balls is the Maxwellian Distribution times v, also called Modified Maxwellian Distribution

const₃ *v³ *e^{const₂ *v2} .

This multiplication with v is also necessary for calculating the flow rate . The real velocity distribution is more narrow than the Maxwellian distribution and it's maximum is at a little higher speed; that's the reason why the real velocity distribution is called modified Maxwellian distribution.
The correct name of the experiment would therefore be "Modified Maxwellian Distribution".
This is also described and verified with many experimental results, e. g. in the journal Physical Review, Volume 99, Number 4, August 15, 1955, pages 1314-1321, article "Velocity Distributions in Pottasium and Thallium Atomic Beams" from R. C. Miller and P. Kusch.
See also the book "Fundamentals of Statistical and Thermal Physics" from Frederick Reif, Chapter 7.12 (Effusion).
In the german version of this book, "Statistische Physik und Theorie der Wärme", from Frederick Reif, 3. Aufl., ISBN 311011383X, you can find it on page 322.

The reason of the misconcept that the Maxwellian Velocity Distribution can be measured directly with a flux of a model gas has been caused in the middle of the 20th century by some layman, e. g. with the (wrong) article "Modellversuch zur kinetischen Theorie" in Beiträge zum mathematisch-naturwissenschaftlichen Unterricht, Heft 8, März 1962, page 1-22, at page 14.
And others have copied the error without a check.
There are many examples for similar copy and paste errors, e. g. the length of the Rhine, wich is 1233 km, but almost every source used a length of 1320 km (+87 km) from the middle of the 20th century till 2010, because someone made an error which was copied without a check: http://www.sueddeutsche.de/wissen/940/507105/text/.
Another example is the legend of the "very high iron content" of spinach with a value of 35 Milligramm / 100 g, which is only one thenth in reality.