Brownian Motion
The continuous random zigzag movement of colloidal particles caused by uneven bombardment from surrounding molecules.
Formula / equation
⟨x²⟩ = 2Dt
Unit
m²/s
In depth
First observed by Robert Brown in pollen grains and explained quantitatively by Einstein in 1905, the motion provided decisive evidence for the reality of molecules. It also keeps colloidal particles suspended by continually counteracting gravitational settling.
Examples in the real world
Smoke particles jittering under a microscope; Perrin's measurements of Brownian motion yielding Avogadro's number.