Air at 40 o C flow steadily through the pipe. If P1 = 40 kPa (gauge), P2 = 10 kPa (gauge), D= 3d, Patm = 100 kPa, the average velocity at section 2 is V2 = 25 m/s, and air temperature remains nearly constant. What is the average speed at section 1

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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