Brownian Motion Simulator

Interactive simulation of Brownian motion: a large pollen grain (visible) suspended in water and bombarded by countless invisible water molecules. The grain's erratic jiggling demonstrates the reality of molecular motion and was the subject of Einstein's 1905 analysis (confirmed experimentally by Perrin). Three main controls: (1) Temperature slider (50–900 K) — increases molecular kinetic energy, making collisions more energetic and frequent, causing more violent grain motion; (2) Number of molecules slider (50–1000) — affects the statistical averaging of forces; (3) Grain radius slider (14–70 px) — smaller grains receive poorer averaging of collisional forces and move more dramatically. Three toggles: Show molecules (visualize the otherwise invisible molecular bombardment), Trace the grain's path (red line showing erratic random walk), and Slow motion (¼ speed for observation). Real-time readouts: simulation time, displacement from starting position, cumulative collision count, and mean molecular speed (px/s). Buttons: Pause/resume, Reset (restart with current settings), Clear trace. Educational explanation section covers why the grain moves (unbalanced collisions), why temperature matters, why grain size matters, and historical significance (Einstein's molecular evidence). Demonstrates foundational concepts of kinetic theory: molecular motion, random collisions, and temperature as measure of average kinetic energy.