FYKOS Year 27 Series 2 Problem 3 — torturing the piston · FYKOS 27 #27.2.3
Physics · thermodynamics
Problem
We have a container of a constant cross section, which contains an ideal gas and a piston at a height of . First we compress the air quickly (practically adiabatically) by moving the piston to a height of , we hold it there until thermal equilibrium with its surroundings is reached, and then we let it go. To what height will the piton rise immediately? What is the height that it will reach after a very long time? Draw a diagram.Intuitive explanation
This problem traces a gas through three distinct processes: adiabatic compression (fast, no heat exchange), isochoric cooling (held fixed, heat flows out), and then free expansion back to equilibrium. The key insight is recognizing that each stage follows different thermodynamic rules—adiabatic uses , cooling at constant volume uses , and the final state depends on whether the piston can rise freely or is constrained by atmospheric pressure. You'll need to track how pressure and temperature change through each step to predict the piston's behavior.
Intuitive explanation
This problem traces a gas through three distinct processes: adiabatic compression (fast, no heat exchange), isochoric cooling (held fixed, heat flows out), and then free expansion back to equilibrium. The key insight is recognizing that each stage follows different thermodynamic rules—adiabatic uses , cooling at constant volume uses , and the final state depends on whether the piston can rise freely or is constrained by atmospheric pressure. You'll need to track how pressure and temperature change through each step to predict the piston's behavior.