Bernoulli for pipe while P=F/A for Hydraullic press???

[libraryismyhome]

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So, I am ambivalent about this topic due to the two conflicting equations.

(1) Pressure = Force / Area

(2)Bernoulli's equation
P1 + 1/2 dv^2 + dgh = P2 + 1/2 dv^2 + dgh
vA = vA


As the area decreases, by the first equation, pressure supposed to increase.

However, for the Bernoulli's, due to the vA = vA, smaller area --> greater v --> smaller Pressure.

For the most BR passages I saw, I got out of this confusion by using Bernoulli's law for the pipe and P= F/A for the hydraullic press. I would like to know when to use certain equation.

 

[Thirteeen]

So, I am ambivalent about this topic due to the two conflicting equations.

(1) Pressure = Force / Area

(2) Poiseuville's Law:
P1 + 1/2 dv^2 + dgh = P2 + 1/2 dv^2 + dgh
vA = vA


As the area decreases, by the first equation, pressure supposed to increase.

However, for the Poiseuville's law, due to the vA = vA, smaller area --> greater v --> smaller Pressure.

For the most BR passages I saw, I got out of this confusion by using Poiseuville's law for the pipe and P= F/A for the hydraullic press. I would like to know when to use certain equation.

P1 + 1/2 dv^2 + dgh = P2 + 1/2 dv^2 + dgh is NOT Poiseulle's Law. It is called Bernoulli's equation.

Poiseulle's Principle:

Q = pi r^4/8NL (P1-P2)

Where, N = viscosity

 

[libraryismyhome]

P1 + 1/2 dv^2 + dgh = P2 + 1/2 dv^2 + dgh is NOT Poiseulle's Law. It is called Bernoulli's equation.

Poiseulle's Principle:

Q = pi r^4/8NL (P1-P2)

Where, N = viscosity

oh yeah ur right.. just corrected 😀

 

[attixx]

I recently missed a few questions making the exact error in thinking.

I think you pretty much have it right now the way you approach the questions.

Pascal's law: F1/A1=F1/A2 applies to hydrostatics (hydraulic press).

Continuity equation/Bernoulli's applies to hydrodynamics, or fluids in motion.