effective cross section of the cloud is $\sim 2 S(y_0)$, implying that the mass of the RHG that is encountered by the falling cloud is smaller than, but comparable to the mass of the cloud (Murray et al. 1993). During break up, the terminal velocity of the fragments $V_t\propto S^{1/2}$, in accordance with Equation (\[eq:vterm\]). The fragments therefore trail behind the remaining clouds.

The kinetic, and especially the internal energy of the background gas are substantially increased by the end of the simulation. In this model, therefore, the majority of the energy released by the infall of the cloud is deposited into the internal energy of the background gas, primarily by the action of weak shock waves generated by the motion of the infalling cloud. This result supports the assumption of [@LM00] that the rate of energy deposition throughout the galaxy is directly proportional to the total infall rate of WFC’s throughout the system.

Model 2: Supersonic impact of WFC’s
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In Model 1, the WFC attains a terminal speed which is a significant fraction of both $C_h$, and the value of $V_t$ predicted from Equation \[eq:vterm\]. It might also be expected that WFC’s which condense from the RHG would 