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Gravity plays a determining role in the evolution of the molecular ISM. In\citet{2016arXiv160304342L}, we proposed a measure called gravitational energyspectrum to quantify the importance of gravity on multiple physical scales. Inthis work, using a wavelet-based decomposition technique, we derive thegravitational energy spectra of the Orion A and the Orion B molecular cloudfrom observational data. The gravitational energy spectra exhibitpower-law-like behaviours. From a few pc down to $\sim 0.1 $ pc scale, theOrion A and Orion B molecular cloud have $E_{\rm p}(k)\sim k^{-1.88}$ and$E_{\rm p}(k)\sim k^{-2.09}$, respectively. These scaling exponents are closeto the scaling exponents of the kinetic energy power spectrum of compressibleturbulence (where $E\sim k^{-2}$), with a near-equipartition of turbulentversus gravitational energy on multiple scales. This provides a clear evidencethat gravity is able to counteract effectively against turbulent motion forthese length scales. The results confirm our earlier analytical estimates. Forthe Orion A molecular cloud, gravity inevitably dominates over turbulenceinside the cloud. Our results provide a clear observational proof that gravityis playing a determining role in the evolution these molecular clouds from thecloud scale down to $\sim 0.1\;\rm pc$. { However, turbulence is likely todominate in clouds like California. } The method is general and should beapplicable to all the astrophysical problems where gravity plays a role.

Probing the multi-scale interplay between gravity and turbulence - Power-law like gravitational energy spectra of the Orion Complex