1. The problem statement, all variables and given/known data A horizontal cylinder with length L=1m and section S=2*10^(-3) is divided in two parts by a piston. In theese compartments is air at pressure p0=10^5N/m^2 and same temperature. The piston move with h=0,4m from initial position. Which is force to hold piston in this position ? 2. Relevant equations My Tries: just this figure and same irrelevant ecuations like PV=nRT and i think P0V0=P1V1, but i dont know why. Thank you very much, i am at begining with thermodynamics.