Walter Lewin (October 4, 1999). Work, Energy, and Universal GravitatioT Course 8.01: Classical Mechanics, Lecture 11 (ogg) (videotape) (in English). Cambridge, MA USA: MIT OCW. Event occurs at 1:21-10:10.
Mohr, Peter J. (2008). "CODATA Recommended Values of the Fundamental Physical Constants: 2006" (PDF). Rev. Mod. Phys. 80: 633–730. doi:10.1103/RevModPhys.80.633.
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