# Water pressure depth vacuum?

Recently I saw an article describing Static Fluid Pressure which says "The pressure exerted by a static fluid depends only upon the depth of the fluid, the density of the fluid, and the acceleration of gravity"

I have 3 water tanks A,B and C with exact same volume, water tank B gets narrower when towards the top like in picture, so it should have more pressure than the tank A which is shorter right, because of B's increased depth.

I have simple question, What if Tank C has an upside down narrow tank inside of it and is vacuum so water gets pulled up into it to a point where the height of the water is same as Tank B. Will the water pressure of tank C be equal to tank B? Given density of fluid and gravity are same in all cases?

I don't have any knowledge when it comes to fluid dynamics so please forgive me if this question sounds stupid.

## 2 Answers

Nice diagrams! A more complete statement would be "The pressure exerted by a static fluid relative to atmospheric pressure depends only upon the depth of the fluid relative to the surface exposed to atmospheric pressure, the density of the fluid, and the acceleration of gravity."

Following this statement, the pressure at the bottom of tanks A and C is the same and is less than the pressure at the bottom of tank B. The pressure in the space marked "vacuum" is actually the vapor pressure of the liquid at that temperature. The dependence on temperature is strong (exponential), so C can serve as a thermometer if you add a length scale to the top.

• "surface exposed to atmospheric pressure" part explains it perfectly. Thanks Mar 1, 2018 at 19:09

Hi I'm not expert but I'm researching similar situation :) So Im 99% sure A and C equal pressure at the bottom exit port if the open surface water hight are the same both tank.