(0.5,1.1, and 1.9 polystyrene particles in water, from Exploring
Squishy Mterials at Emory University)
Brown, Phil. Mag. 4, 171 (1828)
- Irregular motions of small grains
in water were observed soon after advent of microscopes.
- Early microscopy observations were interpreted
as motions of living creatures.
- Brown showed that inorganic grains in suspension
show similiar irregular motion.
Squishy Mterials at Emory University (Brownian
Motion Movies - offline)
Einstein, Ann. d. Physik 17, 549 (1905)
(C.R. Acad. Sci 146 530, 1908) equation for the particle:
- For a sphere of radius a ,
in a fluid of viscosity η , the mobility is given by μ=1/(6πηa)
- The stochastic force is uncorrelated at different times, <f(t)
where D is
the diffusion coefficient.
- To ensure the correct Maxwell-Boltzmann distribution at
a temperature T
mobility and diffusion must be related by
was awarded the 1926 Nobe Prize (lecture,
for expeimental verification (1905-12)