The relative role of turbulence, magnetic fields, self-gravity in star formation is a subject of intensive debate. We present IRAM 30m telescope observations of the $^{13}$CO (1-0) emission in the Serpens G3-G6 molecular cloud and apply to the data a set of statistical methods. Those include the probability density functions (PDFs) of column density and the Velocity Gradients Technique (VGT). We combine our data with the Planck 353 GHz polarized dust emission observations, Hershel H$_2$ column density. We suggest that the Serpens G3-G6 south clump is undergoing a gravitational collapse. Our analysis reveals that the gravitational collapse happens at volume density $nge10^3$ $rm cm^{-3}$. We estimate the plane-of-the-sky magnetic field strength of approximately 120 $mu G$ using the traditional Davis-Chandrasekhar-Fermi method and 100 $mu G$ using a new technique proposed in Lazarian et al.(2020). We find the Serpens G3-G6 south clumps total magnetic field energy significantly surpasses kinetic energy and gravitational energy. We conclude that the gravitational collapse could be successfully triggered in a supersonic and sub-Alfv{e}nic cloud.
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