Fluid Pressure and Density

[drillers]

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I need help; I am not getting the relationship between density and pressure in pipes

In EK 1001 #580, as the SG (density) doubles, the pressure doubles (that's what the answer says anyways)

And that makes sense to me b/c d=P(MW)/RT

In EK 1001 #592: A "which of the following is NOT true" question.

They have that "as the pressure increases in ideal fluid, the density remains the same" as a TRUE statement, but in #580, the density doubled so the pressure doubled.

So which is it? Any thoughts?

 

[sps27]

One is a gas the other is a liquid, that's why. Liquids and Solids are essentially incompressible i.e., little or no volume change upon application of pressure, hence density remains the same (mass is also not changing upon application of pressure). But in the case of a gas, we have volume change on applying pressure.

 

[drillers]

Okay, I think I got it and that makes sense.

d=P(MW)/RT is applicable for gases

while for liq/solids d=m/v where mass and volume are not changing.