  Granular flows and vibro-fluidised granular gases have been extensively
studied recently; most of the theoretical analyses and the experimental
descriptions use temperature and other thermodynamics concepts. However, taking
the very simple case of a vibro-fluidised gas made of identical particles, we
show the lack of efficiency of such concepts for the understanding of the
physics of such systems. This results from both (i) the fact that the vibrator
does not transmit the same amount of energy to each particle, but an amount
which depends on its mass and/or its size and (ii) from the fact that it is a
strongly dissipative medium. We conclude that most experimental device works
rather as velostat as a thermostat. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn
