# Physical meaning of same pressure on the same plan (hydrostatic paradox) with different weight above them [duplicate]

In this picture the points on red have the same pressure because the weight of the fluid is the same above them. But according to pascal law the point on black must have the same pressure(both 3 points are on the same plan),but the weight of the fluid above the point on black isnt the same. So how do we explain this?

## marked as duplicate by sammy gerbil, Jon Custer, peterh says reinstate Monica, Qmechanic♦Sep 20 '18 at 1:49

• The top of the horizontal tube exerts a force on the liquid in the region of the black point which stops the fluid flowing out. – Farcher Sep 17 '18 at 17:13
• So the pressure are equal on both points? That's right? – Maickel Tawdrous Sep 17 '18 at 17:17
• Yes because if the pressures at the same horizontal level were not the same the fluid would move. – Farcher Sep 17 '18 at 17:19
• But if we apply hydrostatic formula we willn't find the same pressure,because the height isnt the same on black point. Except we choose the surface in contact with air as (Z=0). – Maickel Tawdrous Sep 17 '18 at 19:46
• Possible duplicate of Pressure at base of 3 different dam designs – sammy gerbil Sep 19 '18 at 1:09

• At hydrostatic equilibrium, the pressure varies with vertical position z according to the equation $dp/dz=-\rho g$, where $\rho$ is the density, and it is independent of horizontal position. – Chet Miller Sep 17 '18 at 23:13