This is a simulation of Brownian motion of 5 particles (yellow) that collides with a large set of 800 particles leaving 5 blue trails of random motion with one yellow particle with a red velocity vector represented. 

Brownian motion (named after the botanist Robert Brown) or pedesis is the presumably random drifting of particles suspended in a fluid (a liquid or a gas) or the mathematical model used to describe such random movements, which is often called a particle theory.

The mathematical model of Brownian motion has several real-world applications. An often quoted example is stock market fluctuations, although Benoit Mandelbrot rejected its applicability to stock price movements in part because these are discontinuous. 

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