About this app
In 1827, the Scottish botanist Robert Brown observed that tiny particles released from pollen jittered continuously in water. He later saw the same motion with inorganic particles, showing that it was not a sign of life. The phenomenon became known as Brownian motion.
Today, we understand Brownian motion as the result of countless collisions between a larger particle and the rapidly moving molecules around it. The purpose of this simulation is to make that process visible: many small colored particles collide with a larger brown particle, and each collision gives it a tiny push. Because those pushes arrive from constantly changing directions, their combined effect generates the characteristic random path of Brownian motion. The yellow trail makes that path visible.
You can adjust the temperature to change the particles' speed, or hide all the particles to focus on the path alone. You can also click and drag the brown particle to move it around.