19041

I think this article ignored the major reason that large particles rise to the surface. The laws of inertia and momentum indicate that larger particles don’t react as quickly as smaller particles do at the end of each back-and-forth shake of the container. This means there is a force for relative motion between different-sized particles. Just as a basketball will roll over a tennis ball when they collide, so larger particles when they collide will tend, despite their weight, to ride up over smaller ones.