Our studio guest: Prof. Ingo Rehberg of Bayreuth University

"Suppose you are skiing in the mountains and a avalanche tries to bury you. You have a problem, you can circumvent this problem by inflating a balloon that you carry on your back. You will then be treated by the avalanche like a brazil nut. You will swim, you will float on top of the avalanche."
DW-TV: Professor Rehberg, how can this knowledge about sand help us in everyday life?


Ingo Rehberg: Everyday life is influenced by money. And knowledge about granular matter can help you save some money. Because we are wasting a tremendous amount of money – in the order of roughly speaking 50 percent of our energy processing granular matter. This might not be obvious at first thinking. When one thinks of sand, we don’t process it that much. But if you think of charcoal, for instance, or if you think of almost everything you eat which goes into the factory in form of granular matter. These two examples should be enough to at least indicate that precisely speaking, 80 percent of what we handle in the chemical industry is in the form of granular matter.


DW-TV: Now there is an effect called the Brazil nut effect which we’ve all experienced anytime we’ve bought a bag of musli and the raisins are all floating on top. In what other areas can this effect be useful?


Ingo Rehberg: An almost funny or at least bizarre example is the so-called avalanche balloon. Suppose you are skiing in the mountains and a avalanche tries to bury you. You have a problem, you can circumvent this problem by inflating a balloon that you carry on your back. You will then be treated by the avalanche like a brazil nut. You will swim, you will float on top of the avalanche. You might still break your neck, but you will at least be found finally and get a decent funeral.


DW-TV: And there have been experiments carried out where this effect works.


Ingo Rehberg: It works – it has been tested with dummies on a very large scale. And it has also been tested on humans and they all survived – that is the good news.


DW-TV: What are the biggest difficulties when it comes to researching sand especially as every grain of sand can be a different shape and size?


Ingo Rehberg: In fact this is one of the primary obstacles, that they all have different shapes. And in order to express it very clearly, sand doesn’t behave like a fluid and it doesn’t behave like a solid body. Everybody knows that when you imagine a pile of sand. It will stay there for years if you don’t touch it. It is behaving like a solid body. On the other hand sand, when running through an hourglass, behaves more like a fluid. The problem is to find the right mathematics describing both at the same time.


Interview: Heather DeLisle