What is the term for the random movement of particles in a fluid?

The term for the random movement of particles in a fluid is Brownian motion. This phenomenon is observed when microscopic particles, such as pollen grains or small dust particles, are suspended in a fluid (liquid or gas) and move erratically due to collisions with the molecules of the surrounding medium. This movement is not uniform and can vary in direction and speed, reflecting the kinetic energy and random motion of the fluid's molecules.

Brownian motion is significant in various scientific fields, including physics, chemistry, and biology, as it provides insights into the nature of matter and the thermal motion of particles. It was first observed by the botanist Robert Brown in 1827, and it serves as evidence for the existence of atoms and molecules, contributing to the development of atomic theory.