The brazil nut effect is the phenomenon where big particles end up on the surface when a mixture of granular material of different sizes is shaken. The term was based on the observation that, when a container of mixed nuts is opened after it has been shaken, the brazil nuts tend to be on top. The same effect is seen in packets of breakfast cereal containing particles of different sizes, such as muesli. A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). ... Binomial name Bertholletia excelsa Humb. ... The examples and perspective in this article may not represent a worldwide view. ... Muesli (müsli in German or birchermüesli in Switzerland, pronounced [mju:z li] in English and [my:s li] in German) is a popular breakfast dish (breakfast cereal) based on uncooked rolled oats and fruit. ...

There are several possible explanations for this counter-intuitive effect:

1. When shaken, the particles move in vibration-induced convection flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall.
2. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
3. Including the effects of air in spaces between particles, larger particles may become buoyant or sink.

The effect is of serious interest for some manufacturing operations; once a homogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densities of the particles, the pressure of any gas between the particles, and the shape of a container. A rectangular box (such as a box of breakfast cereal) or cylinder (such as a can of nuts) works well, while a cone-shaped container results in what is known as the reverse brazil nut effect. Convection is the transfer of heat by currents within a fluid. ... Look up air in Wiktionary, the free dictionary. ... In physics, buoyancy is an upward force on an object immersed in a fluid (i. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Pressure (symbol: p) is the force per unit area acting on a surface in a direction perpendicular to that surface. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... A right circular cylinder In mathematics, a cylinder is a quadric, i. ... In common usage and elementary geometry, a cone (Greek: κώνος) is a solid object obtained by rotating a right triangle around one of its two short sides, the cones axis. ...

External links

• PhysicsWeb: The Brazil Nut Effect
• Physical Review Letters: Effects of Air on the Segregation of Particles