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'Laptop Experiments'

The GIT is very much involved in scientific popularization: conferences, exhibitions, articles, films... 

Different "laptop experiments" have been constructed for this purpose. Most of the time, they are exposed in our "exhibition" room, where they can be demonstrated to the students and colleagues when visiting the lab. Also, we bring them outside of the lab, in the context of scientific popularization manifestations such as "Science en fête" or "L'Exposition de Physique".


The lab owns a small Taylor-Couette flow with a very small gap and two cylinders rotating independantly.

You can see here a realization of the Barberpole Turbulent pattern


Magic scales

In order to weight the grains:

At the beginning of the experiment, both scales are switched of. The grains are in the tank n°2, which is upside down. The door between both tanks is closed. (see figure 1)

Switch on the scale N°1. Open the door between both tanks. The grains fall down in tank n°1 and are weighted. If you tap the tank, the weight remains stable. Close the door again. Turn the whole device up side down (see figure 2). Switch on the scale N°2. Open the door. the grains fall down in tank n°2 and are weighted.

The weight is different from the first time! And if you tap the thank, the weight fluctuates strongly!!!

What does it happen here?

Granular materials, because of solid friction have a general tendancy to form arches through which the forces are transmitted. These arches transmit the weight to the  side walls of the thank.

The tank n°1, in which takes place the first part of the experiment has a bottom, which is in contact with the scale. Wether the weight is transmitted to the walls or to the bottom of the thank, will not change the weight. All the efforts end onto the scale.

On the contrary the tank n°2, in which take place the second part of the experiment has no bottom and its lateral walls are sustained by the surrounding. As a consequence the scale does not weight the efforts reported onto the walls. And the apparent weight is weaker. When you tap the tank, the forces network and the arches are modified, thus the apparent weight.

And this small device reproduces earthquakes in the lab!...


Finally, the pictures below illustrate various aspect of segregation in granular media


#979 - Last update : 11/04 2009


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