What is Brownian Motion?

The term 'Brownian motion' (or 'Brownian movement') refers to the apparently random, haphazard movement of microscopic particles which are suspended in a fluid - (a liquid or a gas) resulting from their collision with the quick atoms or molecules in the gas or liquid.

This is a simulation of the Brownian motion of a big particle (dust particle) that collides with a large set of smaller particles (molecules of a gas) which move with different velocities in different random directions.

Although a number of earlier workers had observed this phenomenon, it was first described, and therefore named after, the British botanist, Robert Brown, who was studying pollen grains in 1827. Brown was an accomplished microscopist. It was he who, for example, first identified the naked ovule in the gymnospermae; this is a difficult observation to make even with a modern instrument.

Brown was attempting to further his work on the mechanisms of fertilisation in flowering plants and was looking at pollen.  He believed that he would be able to examine the pollen grains more effectively through his microscope if they were suspended in water, a technique known as 'water-immersion'. To his annoyance, he observed that the pollen grains danced continuously and erratically around in the water, thus interfering with his observations. From these observations he satisfied himself that the movement:

'arose neither from currents in the fluid, nor from its gradual evaporation, but belonged to the particle itself'.

Decades later, Albert Einstein published a paper in 1905 that explained in precise detail how the motion that Brown had observed was a result of the pollen being moved by individual water molecules.

Despite all of this knowledge, scientists continue to be fascinated by the origin and nature of Brownian motion, which is still imperfectly understood. Articles concerning the mathematics of Brownian motion continue to be published in contemporary physics journals.

For more information visit:-

http://en.wikipedia.org/wiki/Brownian_motion

http://h2g2.com/edited_entry/A6083633