Why did pressure decrease above the piston?

Question

I can understand the pressure increase below,but why did pressure decrease above as more bricks were added?

Solar Mike · Accepted Answer · 2023-04-03 15:44:55Z

1

Because as the piston was moved down by the mass of the bricks the volume above the piston was increased.

With the valve closed then the fluid expanded to still fill that increased volume and the pressure decreases.

answered Apr 3 at 15:44

Solar Mike

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$\begingroup$ Isn't oil incompressible, though? $\endgroup$
– Osvaldo Silva
Apr 3 at 16:58
$\begingroup$ oil is considered "nearly" incompressible in most applications. Small changes in volume can increase/decrease pressures dramatically in a closed system. $\endgroup$
– Todd Takala
Apr 3 at 22:03
$\begingroup$ "Isn't oil incompressible, though?" It might be incompressible but it is pressurisable (if that's a word). Think of water pressure increasing with depth in the ocean. It's not compressed but it is under increasing pressure with depth. $\endgroup$
– Transistor
Apr 4 at 7:21
$\begingroup$ @OsvaldoSilva check out engineeringtoolbox.com/bulk-modulus-elasticity-d_585.html then think about what might happen to a fluid subjected to reduced pressure... gas coming out of solution? $\endgroup$
– Solar Mike
Apr 4 at 7:34

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