>>14278047>first of all, how does going faster => lower pressure?The velocity of a fluid is the average velocity of all the particles. A fluid at rest has some particles in it which are moving at hundreds of meters per second, but the average velocity is zero. The average speed (not velocity) of the fluid is determined by the temperature. A hotter fluid has more energetic particles. This is technically incorrect, as the temperature correlates with the average collision force of particles, but the simpler definition serves for this explanation.
Now consider what happens if we reorient these moving particles so that they move in a more organized way, that is, so that their average velocity is not zero. We will observe the fluid to be moving. Note that the temperature of the fluid hasn't changed, so the average speed of the particles is the same. It's just that more of them are moving in the same direction.
The pressure exerted by a fluid on its surroundings results from collisions of the particles with their enclosing surface. How will these collisions change if the particle velocities are reoriented so that they have a smaller component normal to the wall? So if we have water in a pipe, what happens if we reorient the fluid particles so that they are all moving in the direction of flow? This is thermodynamically impossible, but it does serve to show that no fluid particles will collide with the pipe, and thus the fluid would not exert any pressure at all on the pipe. This is the essence of the Bernoulli effect.
>second, if I follow the POV of a fluid particle what caused it to accelerate?If we consider an airfoil in a wind tunnel, the leading tip of the airfoil will cause the air in its vicinity, traveling normal to the tip, to come to a complete stop. This leads to an increase in pressure at the leading tip (think car pileup). The air then moves from the high pressure region to lower pressure regions above and below the airfoil, accelerating as it does so.
