November 4, 2011

5.11 Brownian motion

5.11 understand the significance of Brownian motion.

What is Brownian motion?
The English Botanist Robert Brown presented the first evidence that matter consists of tiny particles in motion. Brown was studying pollen grains suspended in a liquid with a microscope and noticed the haphazard movement of the grains, this similar motion can also be seen when smoke particles in air are observed under a powerful microscope. The zigzag motion is due to unequal bombardment between the suspended particles and the molecules of the surrounding medium. This irregular motion of suspended particles is known as Brownian motion.

Why is it significant?
Brownian motion was the first step into proving atomic theory, and although it was Einstein that finally described the physics behind the phenomenon, the motion was named after Brown because he was the first to test this theory. So without Robert Brown, we may perhaps have not had such a conclusive theory until a much later date, or we may have had a different theory all together.

The video below visually explains the motion: the Red disc represents large smoke molecules and the small ball bearings represent the small particles that are usually to small to see.

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