ELI5: Explain Like I'm 5

Brownian motion of sol particles

Brownian motion is the movement of tiny particles floating in a liquid (like water!) or gas. These particles are too small to be seen by the human eye, but when you look at the liquid with a special microscope, you can see that the particles are bouncing around in all directions. The particles bump into each other and move around randomly. This type of movement is called Brownian motion.