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Q & A: expanding piston with water

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Most recent answer: 07/21/2020
Q:
My question is related to generation of vacuum.Suppose I have a cylinder and air tight piston with water in it.I I move the piston 1.whether vacuum will be generated or water expands.But according to me vacuum should generate as water is in compressible.2.Another question is the force required to pull the piston remain constant or it increases with distance?and if so why?I plead you to help me in this regard as i have been trying to find the solution for this question since long time.
- ayub (age 32)
India
A:

As soon as you start to make a vacuum, the water will start to bil until the vapor pressure equals the vapor pressure of the water at whatever temperature it's being kept. This will continue as you slowly expand the volume until all the water has turned into gas. Further expansion will leave a lower-density gas filling the space.
If you pull the piston out quickly, the rapid evaporation will cool the water temporarily, until heat can flow in from the surroundings.

On another issue, no material si incompressible. That's just an approximation useful for some purposes.

Mike W.


(published on 07/21/2020)

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