Consider a piston-cylinder arrangement with an ideal gas inside the cylinder. The region outside this arrangement or thermodynamic system is absolute vacuum. The piston has some mass and initially everything is in equilibrium. The inner surface of the cylinder is rough hence friction force comes into picture when there is relative motion between the piston and the cylinder. Now let the gas be compressed very slowly i.e the process is a quasi-static process (imagine infinitesimally small amount of weights being placed over the piston one by one). Now prove that is process irreversible using the most basic definition of irreversibility alone. Neglect radiation. Definition: A process is said to be irreversible if it can be brought back to its original state without leaving any impact on the universe.