Nutty Brazilian Physics

An undertaking of Brian Ziegler and J D Hoekman

Anyone who has opened a can of mixed nuts knows that the larger nuts tend to be at the top. Do the manufacturers put them in like that? And if so, why? If not, why do the nuts segregate? This segregation of larger particles to the top is known as the Brazil-nut effect.

    This phenomenon not only applies to nuts, but to granular media in general. It is a problem that has been studied since the 1930’s and is still not fully understood. The dynamics surrounding this phenomenon have been studied for a long time because of their importance to industry. When a company makes a product using granular materials it may be necessary for the materials to mix and stay mixed. Imagine a pharmaceutical company mixing two materials for a drug and then having the materials segregate because of random vibrations somewhere in production. It is easy to see the importance of understanding why and how this is happening. Over the years there have been a number of different theories such as sieving, percolation, reorganization, and condensation. None of these has quite nailed down the mechanics completely as there always seems to be a situation that breaks with the theory. Recently there has been research that shows air pressure to be a key factor in this segregation. We are proposing a project to study the effects surrounding air pressure and friction have on the segregation of the larger "Brazil-nut" particle.