Hot Air Balloon: Buoyancy & Thermodynamics Lab (2D)

This 2D companion replaces the 3D version's decorative floating-balloon animation with the physics its title actually promises: air is modelled as an ideal gas, so the envelope's hot air and the ambient air outside it have genuinely different densities at the same local pressure, and the resulting buoyant-force gap — scaled by envelope volume and local air pressure, which itself thins with altitude — is what lifts the balloon. Hold the burner to drive the envelope temperature toward its ceiling; release it and Newton's law of cooling pulls it back toward ambient. A side panel exposes envelope volume, burner rate, payload mass, ambient temperature and crosswind, plus vent and ballast controls for the two classic ways real pilots trade one variable for altitude, while a live readout tracks altitude, vertical speed, envelope temperature, both air densities, buoyant force, weight and net force in real time.