Gas processes.
A toy for the four canonical ideal gas processes. The piston-cylinder on the right has about fifty little molecules; the PV diagram on the left has a single state point you can drag. Pick a process — isothermal, adiabatic, isobaric, or isochoric — and the point stays glued to the corresponding constraint curve as you drag. The molecules animate to match: adiabatic compression visibly speeds them up, because the work you do on the gas with no heat exchange goes into kinetic energy. Build a Carnot cycle by alternating two isotherms and two adiabats; the closed loop appears as your trail and the area inside is the net work.
What you're looking at.
The state of an ideal gas lives in three numbers: P, V, T — and the ideal gas law PV = nRT pins any two given the third. A process is a path through this three-dimensional space; the four canonical ones each hold one quantity fixed: isothermal (T fixed), isobaric (P fixed), isochoric (V fixed), adiabatic (Q = 0, no heat in or out — the gas heats up under compression and cools under expansion).
Energy is bookkept by the first law: ΔU = Q − W, where W is the work done by the gas (positive on expansion) and Q is heat absorbed by the gas (positive in). The stats panel tracks all three since the last reset. On a closed cycle ΔU returns to zero; W and Q can sum to nonzero — the area enclosed by the loop on the PV diagram is the net work.
Try this: pick a low-V, high-P starting point with isothermal expansion; switch to adiabatic expansion; switch to isothermal compression at the lower temperature; switch to adiabatic compression back to start. That's a Carnot cycle, and the closed loop is your engine's signature.