How can I calculate gas pressure in a cylinder using mathematical formulas?

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  • Thread starter Thread starter Crazymechanic
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Discussion Overview

The discussion revolves around calculating gas pressure in a cylinder with a moving piston, focusing on the application of mathematical formulas related to gas laws and thermodynamics. Participants explore various approaches to determine the pressure at the piston’s maximum upper point, considering ideal gas behavior and potential heat transfer effects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant requests a formula for calculating gas pressure in a cylinder with a moving piston, specifying known parameters like stroke diameter.
  • Another participant cites the ideal gas equation PV=nRT, rearranging it to express pressure as p = nRT/V, but notes uncertainty regarding the "abstract cylinder" context.
  • A different participant argues that the ideal gas equation alone may not suffice, suggesting that information about heat transfer is necessary and mentioning the adiabatic expansion/compression equation as a potential alternative under certain assumptions.
  • Another participant provides a formula for the change in volume as Pi*r^2*s, indicating that assumptions about volume and temperature relationships are needed to incorporate temperature into the calculations.
  • One participant expresses gratitude for the insights shared in the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a single formula or approach, with multiple competing views regarding the applicability of the ideal gas law and the need for additional considerations like heat transfer.

Contextual Notes

Participants highlight the need for assumptions regarding heat transfer and the relationship between volume and temperature, indicating that the discussion may depend on specific conditions not fully articulated.

Crazymechanic
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Hi could you please help me out with a formula?
So imagine this abstract cylinder and a piston moving in it , I have let's say an x amount of gas in it and all the other parameters like stroke diameter and so on , by what formula could I calculate the pressure that the gas will have when the piston will reach it's maximum upper point?
 
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PV=nRT is the ideal gas equation.

I'm not sure if I'm missing something related to an "abstract cylinder"...

Re-arranging for pressure give p = nRT/V

p = pressure
n = number of moles of gas
R = 8.31
T = temperature in Kelvin
V = Volume of containerI hope that helps
 
The ideal gas equation (and note the word 'ideal'; in practice, things can be a bit different) won't be enough to give you an answer. You will need to supply information regarding heat transfer. If you make the simplifying assumption that things happen too quickly for any significant heat flow than you can also use the adiabatic expansion/compression equation. (q.v.)
 
note that the change in volume will be Pi*r^2*s, where r is the radius of the piston, s is the distance it moves.
you are going to need to assume the volume and temperature have some kind of relation from thermo laws to deal with T in the equation.

you could prolly use P=f(V) and use derivitaves to get the change.
 
Thank you for giving me insight:)
 

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