Adiabatic vs Isothermal Processes on a PV Diagram

What you are seeing: two reversible processes from the same starting state. Isothermal: $PV = nRT$ . Adiabatic: $PV^\gamma =$ const, which is steeper. Watch the gas piston compress and expand along the chosen curve, and the temperature track the volume.

Figure 1. Isothermal (cyan) vs adiabatic (orange) reversible processes from the same initial state.

γ (gas)1.40

T_0 (K)300

process

WHAT TO TRY

Compress the gas both ways: the isotherm PV = nRT and the adiabat PV^gamma = const start together, but the adiabat is steeper because no heat escapes and the trapped energy heats the gas.
Raise gamma toward 5/3 for a monatomic gas and the adiabat steepens further: fewer internal degrees of freedom mean compression heats it more.
Switch to adiabatic only and watch the temperature climb on compression, the reason a bicycle pump warms and rising air cools as it expands.