One of the common misunderstandings regarding Bernoulli's principle is that, in general, "faster moving air has lower pressure".

Bernoulli's principle can only be applied to asingle streamline in absence of friction, and measurements of streams generated by fans, hardryers or simply air blown from one's lungs shows that static pressure inside those streams is exactly equal to atmospheric pressure. Equivalently, "a free air stream in the atmosphere is exclusively decelerated by friction".

While I understand that Bernoulli's principle can't be applied in these situations, I'm not clear on why a free air stream would always have exactly atmospheric pressure. Could someone explain that to me?


1 Answer 1


May it now be that by definition a free stream has no accelerations? And as derived in the linked page, no acceleration implies no pressure gradients. That with the fact that all the streams considered are connected with the atmosphere at some points, should mean all the stream is at atmospheric pressure.


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