Heat & thermodynamics › Brownian motion
Brownian motion laboratory
Follow a suspended particle as countless uneven molecular impacts produce a random walk and measurable diffusion.
What to notice
The large particle is struck unevenly by much smaller, faster molecules. Its individual path is unpredictable, but the mean-squared displacement of many trials grows approximately linearly with time. Higher temperature increases diffusion; greater viscosity or particle radius reduces it.
D = kBT/(6πηr) · ⟨r²⟩ = 4Dt in 2D · m dv/dt = −γv + Frandom + Fexternal
Educational reduced-order model. Brown observed pollen motion in 1827; Einstein explained its statistics in 1905, and Perrin’s experiments helped confirm atomic theory.