Pitot Tubes and Static Pressure

[Abhishek Jain]

Hey so I am learning physics on Khan academy and they had a video on Pitot tubes:

https://www.khanacademy.org/science/physics/fluids/fluid-dynamics/v/venturi-effect-and-pitot-tubes

I had a question. I understand that the lower part of the pitot tube in the video is measuring the pressure experienced when the air is not moving (i.e. stagnation pressure). I also understand that the top tube is measuring static pressure. However, I don't understand how it is doing that? From my understanding, static pressure is the pressure at a given point during the flow of fluid? And total pressure = static pressure + dynamic pressure? Am I misunderstanding what static pressure is? If not, how is it measuring the static pressure? There is no airflow in the tube so wouldn't it be the same as the lower one then (but then there is no air going inside vs the lower tube where as much air as possible is going in)? I am getting very confused the more I try to understand it.

Thanks in advance for the help!

 

[boneh3ad]

If you have air flowing over the tube, the pressure just outside the hole in the top will be the static pressure at that point in the flow. Just inside the hole, in order for there to be no flow in or out, the pressure must be the same as just outside of it, and is therefore the static pressure.