[Title: PI T] [Verse] Hold T, change the volume Internal energy shifts Intermolecular forces matter That is where the change begins [Chorus] Pi T, internal pressure dU dV at constant T Pi T, internal pressure Tells how U depends on V [Verse] Zero means ideal behavior No interaction there Positive when attraction dominates Stronger pull, stronger change [Chorus] Pi T, internal pressure dU dV at constant T Pi T, internal pressure Tells how U depends on V [Bridge] Expand the system, U can change Even when T is fixed That dependence, written clean Is what pi T gives [Final Chorus] Pi T, internal pressure dU dV at constant T Pi T, internal pressure Tells how U depends on V