English: The animation illustrates how the separation in FFF is driven by particle diffusion in a parabolical flow profile. Shown are two types of particles; the red ones are smaller than the blue ones. A force is applied from the top (here it is a cross flow used in asymmetrical flow fff). The particles diffuse up against this force. On average the smaller red particles are higher up above the accumulation wall compared to the blue particles. The elution flow in longitudinal direction is shown with the flow arrows indicating the velocity profile. Particles jumping up higher are transported faster side compared to others. In the statistical process of many particles and many diffusion steps, the cloud formed by the red, smaller particles, migrates faster and separates from the slower blue particles.