2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/17689I calculate the hydrodynamic limit of the BGK approximation of the Boltzmann equation for the case of a long stress relaxation time and find that the stress obeys a viscoelastic constitutive equation. The constitutive equation is different from standard constitutive equations used for polymeric liquids in that it is not ``objective'' because inertial effects are important. I calculate the exact solution for the stresses for simple shear flow and elongational flow.14 pages, 4 figuresStatistical Mechanicstext