Some time ago I asked a question why Dynamic pressure is considered scalar.

Why is the dynamic pressure not a vector quantity?

This still puzzles me so I hope to give a scenario that doesn't make sense to me

If mass fluid flow always occurs from high pressure to low and we consider that Bernoullis tells us that Total pressure is constant along a streamline * how do we explain flow without considering the vectors of the components of that total pressure?

  • Total Pressure along a streamline of unchanging height is constant and is the sum of Static pressure and Dynamic Pressure components ?
  • $\begingroup$ Is there a reason you're singling out dynamic pressure in particular, or does your question apply equally to static pressure as well? $\endgroup$ – CR Drost Mar 4 '15 at 3:13
  • $\begingroup$ Hi Chris, I guess because I understand that (until the atomic scale) that static pressure is completely random (so independent of direction) thus the net force static pressure exerts on a 'parcel' of fluid is zero and does not contribute to flow .However if you think the explanation is improved by considering static pressure as by all means use this approach $\endgroup$ – Quentin Chester Mar 4 '15 at 3:21
  • $\begingroup$ Chris if you watch this video from 5:00 to 6:00 you will see that the flow is explained in form of net forces in front and behind the fluid parcel. youtube.com/watch?v=LI9Mi1KhFTs I Guess that's where I get confused as if we expand Bernoullis to Euler equations that Dynamic Pressure is also explained in the form of vectors (which I understand better than the statement that Dp does not consider vectors) $\endgroup$ – Quentin Chester Mar 4 '15 at 3:36
  • $\begingroup$ Consider something like voltage. If one part of a conductor has a higher voltage, then we expect current to flow. In simple cases like a wire knowing the voltages can immediately lead you to calculate current. But voltage is a scalar quantity with no direction, and it's current which is the vector quantity. Pressure is analogous to voltage. $\endgroup$ – MonkeysUncle Mar 4 '15 at 3:50
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    $\begingroup$ I really don't see how this is not still a duplicate of Define Pressure at a point. Why is it a scalar? $\endgroup$ – ACuriousMind Mar 4 '15 at 15:01

Dynamic pressure means orderly motion. Magnitude and direction are involved. With more than one variable it becomes a vector.

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