Gravity plays a determining role in the evolution of the molecular ISM. In Li \& Burkert. (2016), we proposed a measure called gravitational energy spectra to quantify the importance of gravity on multiple physical scales. In this work, using a wavelet-based decomposition technique, we derive the gravitational energy spectra of the Orion A and the Orion B molecular cloud from observational data. The gravitational energy spectra are found to exhibit power-law-like behaviors. At sub-parsec scale, the Orion 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 close to the scaling exponents of the kinetic energy power spectra of compressible turbulence (where $E\sim k^{-2}$), with near-equipartition of turbulent versus gravitational energy on multiple scales. This provides a clear evidence that gravity is able to counteract effectively against turbulent motion for these length scales. The results confirm our earlier analytical estimates. For the Orion A molecular cloud, gravity inevitably dominates over turbulence inside the cloud. Our work provides a clear observational proof that gravity is playing a determining role in the evolution of star-forming molecular clouds from the cloud scale down to $\sim 0.1\;\rm pc$. The method is general and should be applicable to all the astrophysical problems where gravity plays a role.
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