Brownian motion is the random, erratic movement of small particles suspended in a fluid (liquid or gas), caused by collisions with the much smaller, fast- moving molecules of the fluid. This motion results in particles moving in unpredictable, zig-zag paths when observed under a microscope
. The phenomenon is named after the Scottish botanist Robert Brown, who first observed it in 1827 while looking at pollen grains in water. He noticed that these pollen particles moved randomly without any apparent cause. Later, Albert Einstein provided a theoretical explanation, showing that this motion is due to the continuous bombardment of the suspended particles by the molecules of the fluid, which are themselves in constant thermal motion
. Key points about Brownian motion include:
- It occurs because smaller fluid molecules collide with larger suspended particles, transferring momentum and causing random changes in speed and direction
- The motion provides evidence for the existence and kinetic activity of atoms and molecules in fluids
- The speed of Brownian motion is influenced by particle size (smaller particles move faster) and the viscosity of the fluid (lower viscosity leads to faster motion)
- It helps explain phenomena such as the stability of colloidal solutions, where particles remain suspended rather than settling
Mathematically, Brownian motion is modeled as a stochastic process known as the Wiener process, which is fundamental in probability theory and has applications beyond physics, including finance
. In summary, Brownian motion is the microscopic, random movement of particles suspended in a fluid, caused by collisions with the fluid's molecules, and it serves as direct evidence of molecular motion.
