Bernoulli's Principle

[victorias]

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Why can't we say that the area in III is lower and since P = F/A, P will be higher? So, I thought that since A in I is larger, P will be the lowest. What is wrong with this method? And even intuitively, it seems that when fluid is being squeezed through a narrow space, it would have a greater pressure. Can someone explain this? I don't quite understand their explanation given in the answer.

 

[pennyboard95]

Static pressure + .5pv^2 + pgh = all three combined after

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[pennyboard95]

The static pressure is conserved cause height doesn't change

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[pennyboard95]

The static pressure is conserved cause height doesn't change

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Actually the pgh doesn't change cause center of flow is same in squeezed so in order for the three to add up to same before the static pressure must go down

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[pennyboard95]

Pressure is f/a is the theory of pressure and is useful for hydrolic press. Yes it is not intuitive but if flow increases then pressure goes down because the particles are going more in one direction and pressing less against the sides of tube

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[laczlacylaci]

A rule to have in your mind is as area increases, velocity decreases (continuios eq.) and with the (Bernoulli's equation) as velocity decreases, pressure increases. So we can assume in these questions that as area increases, pressure increases as well, but don't confuse this with the ideal gas law P and vasodilation/constriction cross-sectional area.