**A mes pairs: Gaz granulaire et 2 ^{nd} Principe de
thermodynamique: **

** un gaz "dur",
un gaz de combat, un gaz de débat manqué **

**P. Evesque, **Lab
MSSMat, umr 8579 cnrs, ECP, 92295 Châtenay-Malabry, France , pierre.evesque@ecp.fr :

**Abstract : **

This paper explains
within simple arguments why the physics of granular gas has to be understood in
a new way, different to the one proposed by P. Haff, and able to describe the
energy delivered to it and dissipated by it. This requires to take into account
the difference in the mean particle speed in the + and – ways of the excitation
direction. These different means V_{+ }(=
Smv_{+ }/Sm) and V_{-}(= Smv_{- }/Sm )_{ }exist
mainly everywhere in the sample as shown in P&G**17**, 577 (2009) and P&G**18**,
1,(2010). In steady excitation, which imposes (S_{ }m_{ }v_{+}+S_{ }m_{ }v_{-}) =0, this
generates the existence of a new force │P^{+}│-│P^{-}│,
where P^{±} (= mSv_{±}²) are the mean kinetic pressures in the two ±
directions , due to the fact that the “pressures” P^{±} on the two
sides of a fixed plane are different. This new force was not taken into
account; it is due to the speed asymmetry, combined with a particle-particle
restitution coefficient e smaller than 1.
In the scientific literature, everything is treated has one did want to
deliver energy to the granular gas: the granular system at a local uniform
temperature at the boundary, so that it cannot make any work (second principle
of thermodynamics. It gets heat only from the boundary. If this was true, it
would help mining excavation and treatment. This article tries to understand how
we arrived there there.

**Pacs # : **5.40 ; 45.70 ;
62.20 ; 83.70.Fn ; 45.35i ; 45.70.Mg; 83.80.fg ;
46.80.Ff ; 05.20.-y

*poudres & grains ***20**, 52-67 ( décembre 2012)