the curve representing a polytropic process on a thermodynamic diagram. The equation of the polytropic curve of an ideal gas has the form pVn = const, where p is the pressure of the gas, V is the volume of the gas, and n is the polytropic exponent. Special cases of the polytropic curve of an ideal gas are the isobar, where n = 0; isotherm, where n= 1; isentropic curve, where n = y, in which γ is the ratio of the specific heats at constant pressure and volume; and isochor.