Kinetic Theory & Thermal Physics Simulation
Explore this free thermal physics simulation: connect molecular motion with gas pressure, heating curves, thermodynamics and thermal radiation.
How to use the thermal physics simulation
Choose one of the nine investigations above. Change the numerical controls beside the model and watch the graph below. Teacher view adds three live graphs; Student view keeps the main model and measurement graph. Pause to inspect particle motion, record readings, keep comparison curves or export your results as CSV. Each visit begins with a fresh investigation.
Kinetic theory, pressure and gas laws
Start with Molecules & pressure. Gas particles move randomly and collide elastically with the walls. Each impact changes a particle’s momentum and exerts a force on the wall. Pressure is force per unit area. Compare the fluctuating pressure measurement with its longer average and the ideal-gas prediction pV = NkT. Select a particle to follow its path and velocity.
Next, use Gas laws & temperature. Hold temperature, volume or pressure constant and change the remaining variable. The chart switches automatically to the selected gas-law investigation. Boyle’s law gives pV = constant at fixed temperature. At fixed volume, pressure is proportional to absolute temperature; at fixed pressure, volume is proportional to absolute temperature.
Molecular speeds, collisions and Brownian motion
In Speeds & collisions, compare a sampled speed distribution with the Maxwell–Boltzmann curve. Change temperature or molar mass and inspect the most probable, mean and root-mean-square speeds. The relation ½m⟨c²⟩ = ³⁄₂kT connects mean translational kinetic energy with absolute temperature. Collisions redistribute energy between particles while conserving total momentum and kinetic energy.
The Brownian motion investigation follows a heavier suspended tracer struck by lighter gas particles. Its irregular trail comes from unequal molecular impacts. Hide the surrounding molecules to focus on the tracer. The diffusion option starts with two separated populations and shows how random motion produces net spreading.
Heat, work and internal energy
Select Heat & work, choose a process and press Start process. The piston and p–V graph move together. Compare isothermal, adiabatic, constant-pressure and constant-volume changes. Work done by the gas is the area under an equilibrium p–V path. With Q positive into the gas and W positive for work by the gas, the first law is ΔU = Q − W.
Compare the two staged paths between the same equilibrium states. Their heat and work transfers can differ even when the internal-energy change is the same. Free expansion into a vacuum has no boundary work; for the ideal-gas model, temperature and internal energy remain unchanged. Some processes are extensions beyond particular A-Level specifications.
Heating curves, phase changes and calorimetry
Use Heating & phase changes to warm ice through melting and boiling. Press Start heating after setting the heater power, thermostat and sample mass. The complete temperature–time curve retains both plateaus: 0 °C during melting and 100 °C during boiling at atmospheric pressure. Away from a phase change, Q = mcΔT; during a phase change, Q = mL.
Pale ice particles vibrate about ordered sites. Blue liquid particles move past their neighbours, while gold vapour particles spread through the chamber. The ice-to-water volume change is exaggerated for clarity. Mixing shows two temperatures approaching an energy-conservation prediction. Evaporative cooling shows escaping particles, decreasing mass and falling temperature; its escape rate is illustrative.
Thermal radiation and the Boltzmann factor
In Thermal radiation, adjust emissivity, surface area and surroundings first. The surface-temperature control comes last, close to the graph. Increase temperature to see the spectrum rise and its peak move to shorter wavelengths. Wien’s displacement law gives λmaxT = constant, while Stefan–Boltzmann emission follows P = εσAT⁴. Net power also depends on the surroundings temperature.
The animation uses illustrative colours and rays to show relative emission. The plotted spectrum and power calculations use the model equations. The separate Boltzmann-factor investigation compares populations of two energy levels with equal degeneracy. Increasing temperature makes the upper level more populated, according to the factor exp(−ΔE/kT).
Thermal equilibrium and thermometry
The Thermometry tab brings a sample and probe into contact before energy flows. Watch their temperatures converge and separate them to stop heat exchange. A thermometer measures its own temperature, so it agrees with a sample only after approaching equilibrium. Compare a small probe with two finite samples, then investigate an illustrative NTC thermistor and potential-divider output.
This thermal physics simulation supports AQA, Edexcel, OCR A and OCR B revision, with related material useful for other boards. Check your specification for the exact scope. Particle pictures are enlarged and slowed, and the thermal models use approximate material properties. These simulated investigations support learning rather than replace assessed practical work.
Continue with thermal physics and gas-law exam questions, A-Level Physics questions by topic or more free physics simulations. Maths With Matt provides free resources and online Maths and Physics tuition for students across the UK.
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