# Brownian Motion: Mass and size of Brownian particle

For observation of Brownian motion, the mass and the size of the Brownian particle should be very small. Within what range the size and mass of the Brownian particle should lie?? Can a particle with small mass and bigger size and vice versa can undergo Brownian motion??

anorlunda
Staff Emeritus
Wouldn't the answer depend on the magnitude of the forces?

In the surf of an angry sea, even boulders are tossed around. Ditto for solid objects in a boiling lava pool.

Andy Resnick
For observation of Brownian motion, the mass and the size of the Brownian particle should be very small. Within what range the size and mass of the Brownian particle should lie?? Can a particle with small mass and bigger size and vice versa can undergo Brownian motion??

In the Langevin approach, the magnitude of Brownian forcing scales with temperature and viscosity and inversely with particle mass.

https://en.wikipedia.org/wiki/Langevin_equation

In terms of analysis, I suspect you are looking at the Peclet number (convected flow vs. diffusive motion)

https://en.wikipedia.org/wiki/Péclet_number