Hydrostatic Pressure on wall two fluids (Pressure Prism Method)

Forces on a submerged surface - Fluid mechanics
Hydrostatic Problem Example

Water and oil layer with different specific gravities and depth layers apply a hydrostatic pressure on a wall.

Find the resultant fluid force acting on the wall using pressure prism method

F = (rho)(g)(h)(A)

SG oil = 0.8 rho water.

Location of resultant force requires using moments after finding forces.

[micahangela]

Thank you, sir! You explained this concept way better and easier than my prof did.

[omarbohawiea]

your voice slowly makes me feel want to sleep-good night

[Stephanie-sirs]

The density of water is 1000 kg/m3, not 1 kg/m3 as stated (same logic goes for the oil). Therefore, its specific weight would be 9.807 kN/m3 [water].

Also, the resultant force on a vertical rectangular plane surface is R = p*A, where p is the AVERAGE pressure, which is ALSO equal to the pressure at the centroid of the plane area. [notice it is calculated to the centroid, not the third from the bottom of the triangle, although the force is located at the third from the bottom of the triangle].

The average pressure would be: p = (1/2)*(p1+p2) = (1/2)*ρ*g*(h1+h2) [ρ*g = specific weight]

[AbhijeetKumar]

Thank you very much. I was confused since an hour.

[rudrashishdasgupta]

Density 1000 for water, it's 1 gm/ cc . And .8 specific gravity.

[SkegAudio]

Do you have to take Atmospheric pressure into account in this question? Or you don't since Patm is applied to both sides?

[infocasy]

love you bro, you have a nice concept

[NishantKJha-qkow]

Thanku... It is very helpful for me...

[AMANKUMAR-unpg]

Sir I have a doubt that why not D1 would be the center of pressure for F1 which is calculated by using formula Icg/A(dbar) + dbar .why you and all are using D1 =dbar .you have requested to please clear my doubt

[fahadreda]

What are you mean by 2m into the page it iseam confused to me I think area 1-should be 1*4 and area 2 is 2*4

[juni]

I still can't quite understand why there is a second force (rectangular prism) from the oil. Wasn't the pressure exerted from the oil already accounted for in the first triangular prism. I'm not questioning your answer (i know its right since my textbook says the same), but why is it included in the first place. Thanks.

[abhisekgochhayat]

Hi @Cowan Academy
Can u please explain why did u take centroid distance rather than centre of pressure distance as the hydrostatic force acts through centre of pressure

[jobogutu]

what if it was a cylindrical tank. which surface are do you use?

[BelumCharankumar-reddy]

This question came in gate 2023 mechanical paper

[pappu]

I didn't understand how that force f2 due to oil came since oil is not present below 1m from top

[technicalunikorn]

If we are given three fluids then how many forces that we calculate

[narsinghsv]

why don't we take centre of presure position..?

[bahaablast]

is the centroid of every triangle in every pressure prism 2/3?

[innitbruv]

The density of water is 1000kg/m^3, not 1kg/m^3. I think you account for this by multiplying by 10^3...but I don't think that is correct.

[lyakacatherine]

Why the 1/2 in calculation of F1 and F2