[en] In this paper, three classes of laboratory plasma experiments are investigated in terms of global energy balance relations. The three types of experiment considered are rotating plasmas with radial geometry, typically plasma centrifuges, rotating plasmas with axial geometry, or vacuum arc centrifuges, and linear plasma-neutral gas collision experiments. All three experiments yield plasma velocities close to the Alfven critical velocity for a range of experimental conditions. To explain the experimental observations, it has been postulated that a special interaction occurs whenever the relative velocity between neutral gas and plasma reaches the critical velocity ν_a = (2ε₁/m)^1/2, where ε₁ is the first ionization potential of the neutral particles and m is their mass. Here, we look at the experiments from the energy balance point of view and conclude that it is not necessary to postulate any special interaction occurring at the critical velocity to explain the experimental data