Q:  If a cloud is more massive than this critical value, 
                   will it expand or collapse?



       Look at the virial theorem expressed in terms of the clouds's mass:



                   KE side                      GPE side

                                                     2
                      M                    3      G M  
               3kT ---------         =    ---  -----------
                    mu mH                  5        R



        The KE side has mass "M" to the first power, while the GPE side
        has mass "M" to the _second_ power.  Thus, the GPE side grows
        more quickly with mass.

        If a cloud exceeds the Jeans' mass, it will collapse.