Physics · Study 021
Brownian Pollen
A pollen grain staggers across the screen as hundreds of fast molecules bump into it. Brownian motion, with the hidden cause made visible.
What you're looking at
The small dots are molecules flying in straight lines. Each time one strikes the big grain it bounces off elastically and hands over a little momentum. No single hit matters, but the hits never balance exactly, so the grain wanders along the orange path.
The idea behind it
Robert Brown saw this jitter under a microscope in 1827 and could not explain it. In 1905 Einstein showed that the statistics of the wandering reveal the size of molecules, and Jean Perrin's measurements a few years later settled the argument over whether atoms were real.
Try this
Press and hold to pick the grain up and drop it somewhere else. Restart clears the path.
