Hello. I’ve found in the forum this thread that had the same question I’d thought. https://www.physicsforums.com/showthread.php?t=143593 But there were too much things involved in it. I would like to know if Bernoulli’s principle effects change if the Observer velocity changes. For instance, everyone knows that a ping pong ball floats pushed by air stream. Besides, we know that inside this air “tube”, the air velocity is bigger than the air around it. So, the pressure in the tube is smaller. In this way, if we try to push the ball to one side, it comes back pushed to the middle of the tube by the larger external pressure. My question is: If something is moving inside the ascending tube air to the same velocity that stream (for instance, a fly) it will notice inside the tube a relative air velocity zero. However, outside the tube, it will notice a stream that moves fast in the opposite direction (-V). Will it detect a smaller pressure outside the tube? So, will it be pushed outside the tube? Regards from Spain!!