In the simulation above, 100 blue and 100 red particles start diffusing from a single point, at the upper left corner when first started or where ever the mouse is clicked within the box to restart the simulation.

Note the particles don't spread in a uniform way, however. Even several seconds after the mouse is clicked, they are still mostly concentrated near their original point, with fewer and fewer particles further from that point. Thus, each group of particles creates a concentration gradient down which they gradually diffuse.

Consider for a moment what properties of the particles and their surroundings might affect their behavior and how you might measure their diffusion. Then move on to the next page.