For an adiabatic expansion of an ideal gas, the fractional change in its pressure is equal to (where γ is the ratio of specific heats):
dVV
−1γdVV
−γVdV
−γdVV
Equation of adiabatic process is PVγ=constant PγVγ−1dV+VγdP=0 Or
dPP=−γdVV is the fractional change in pressure.