Thermodynamics visualizer

A kinetic-theory gas box with real measured pressure from actual particle collisions, and a piston sandbox for the four classic PV processes.

Lessons

Pick a topic, read the steps, then try them right in the sandbox below.

Class 11 — Kinetic theory: where pressure actually comes from

Concept: gas pressure isn't magic — it's the real, measurable result of countless particles colliding with the container walls. More particles or higher temperature (faster particles) means more, harder collisions, which means more pressure.

Switch to Kinetic theory gas mode.
Note the starting Pressure (measured) value.
Raise Temperature T and watch the particles visibly speed up — Pressure (measured) should rise too.
Reset the temperature, then instead raise Particles N — pressure rises again, this time because more particles are hitting the walls, not because they're faster.
Finally, drag the Piston (volume) control to shrink the box — pressure rises sharply as the same particles now hit the walls far more often.

Takeaway: pressure isn't one single "thing" — it's the combined effect of how many particles there are, how fast they're moving, and how much space they have.

Class 11 — The four PV processes

Concept: the same gas can be compressed or expanded in different ways — keeping temperature fixed (isothermal), pressure fixed (isobaric), volume fixed (isochoric), or with no heat exchange at all (adiabatic) — and each one does a different amount of work, shown as the area under the curve on the PV diagram.

Switch to PV diagram mode.
Select isothermal and drag Volume V to expand the gas. Note the Work done W=∫PdV value.
Reset, select adiabatic instead, and expand the volume by the same amount. Compare the work done — an adiabatic expansion does less work for the same volume change, because the gas cools as it expands instead of drawing in heat to stay at constant temperature.
Try isochoric (volume fixed) — confirm the work done stays at zero no matter what you do to Temperature, since W = ∫PdV needs the volume to actually change.

Takeaway: "work done by a gas" always means the area under its path on a PV diagram — and that area depends entirely on which of the four processes it follows.

What each mode covers

Kinetic theory gas — real hard-disk particles bounce elastically off each other and the walls; pressure isn't assumed, it's measured from the actual momentum the particles deliver to the moving wall. Compare that measured value against the ideal-gas-law prediction P = Nk_BT/V (they should track closely, with the real fluctuation you'd expect from a finite number of molecules). Raise the temperature slider and every particle instantly moves faster — that is temperature at the molecular level. Push the piston in and watch the measured pressure rise.

PV diagram — pick a process (isothermal, isobaric, isochoric or adiabatic) and move the piston (or, for isochoric, the temperature); the P–V curve traces live and the work done W = ∫P dV is computed from the actual path, using the correct formula for each process — not a single generic approximation.

Idealisations: hard-disk particles with no intermolecular forces except at contact, γ=1.4 (diatomic) for the adiabatic case, and simulation units throughout (k_B=1, nR=1) rather than SI — the physics relationships are exact, only the unit scale is simplified. One more worth naming: in the kinetic-theory gas, pushing the piston in repositions particles but doesn't do work on them the way a real piston would (no compression heating) — temperature only changes when you move the temperature slider yourself. Same honesty-about-simplifications spirit as every other lab in Forces.

Part of Forces — see Learn for the class 11 thermodynamics and kinetic theory topics this maps to.

Test yourself

Pick Class 11 in the physics quiz to test yourself on thermodynamics and kinetic theory — 10 random questions, with an explanation for every answer.

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