Answer to Question #168 in Molecular Physics | Thermodynamics for Ben

Question

Heat-insulated vessel with ideal gas is hanged on a rope in the gravity field. Due to the influence of force of gravity the density of gas in the bottom of the vessel is bigger than in the top. The rope is burned and the vessel freely falls. Supposedly, during the falling has time for forming of thermodynamic equilibrium, define equilibrium gas temperature, which will form in it in time of falling.

Answer 1

The gas temperature will not change. During free fall gas is in state of weightlessness. Initial state is unbalanced - density on the top is less than on the bottom. However, kinetic energy of molecules is everywhere the same. When changing to equilibrium state densities equalize. But full kinetic energy of molecules of gas, defining its temperature, stays constant. The experiment is similar to a well-known experiment by Gay-Lusaka concerning expansion of gas into vacuum