Vibrating powder or sand pushing larger particles to the top



What is the name of the effect where vibrating a powder causes larger particles to move to the surface. Why does it happen?

I’ve seen this numerous times with things like hot chocolate, where shaking the bag moves the sugar crystals on top of the cocoa, or with small pebbles in buckets of sand.

I’ve been looking for videos of what I mean, but I normally just get videos of cymatics, which is not what I’m referring to. The closest I’ve found is this video below, where larger solid chunks of sand can be seen getting pushed out of the rest on the left-hand side

In: Physics

It’s called granular convection or granular segregation. It’s also sometimes referred to as the Brazil nut effect.

There’s space between the particles. When you shake the container, the smaller particles can easier fall through the space create by larger particles touching. These particles don’t actually life the larger ones, but as you shake, all the particles are sometimes jolted upward with the smaller ones falling beneath the larger ones thus preventing the larger ones from falling back down.