On a P–V diagram, work is geometry.

A P–V diagram plots the system’s pressure against its volume, tracing a thermodynamic process.

• State points and paths
• Why path matters for work
• Reading changes in P and V

Quasi-static means the system passes through a sequence of near-equilibrium states, so P and V are well-defined along the path.

• Why “slow” matters
• Internal pressure vs external pressure (conceptual)
• When P–V work formulas apply

Common idealized processes have recognizable P–V shapes and simple work interpretations.

• Isobaric: horizontal line
• Isochoric: vertical line (no P–V work)
• Isothermal: curved path (ideal gas context)

For quasi-static processes, the work done by the gas is the signed area under the P(V) curve: W = ∫ P dV.

• Expansion vs compression sign
• Area interpretation for simple shapes
• Connecting to energy accounting (preview)

Practice reading P–V graphs and computing work with sign conventions and process recognition.

• Work-from-graph drills (areas)
• Identify process types from P–V shape
• Expansion/compression sign checks
• Short explanation prompts (“why path matters”)
• Exam-style mixed P–V sets