Molecular DiffusionJuliette MooreAward: Top 100
School: rye country day school This photo shows dye dropped into a jar filled with cold water. Diffusion is the mixing of molecules due to their random motion. The amount of time before the water and dye diffuse depends on the kinetic energy of the molecules randomly bouncing among each other, called Brownian motion. Because molecules in cold water have less kinetic energy than warm water, diffusion is slower in cold water. When the water is cold and the diffusion rate is slower, more of the dye stays together in a plume falling to the bottom of the container. The dye has a higher specific gravity than water, so before it diffuses, it sinks in the cold water. Because the water is cooler than the air surrounding it, it developed convective flow patterns as the water approached the temperature of the surrounding air. The sides of the container conducted heat to the sides. The cool, denser water at the center sank, and dye added to the sinking center rode the convective flow to the bottom of the container and up the sides. 
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