Energy units are usually defined in terms of the work they can do. However, because work is an indirect measurement of energy, (One example of the difficulties involved: if you use the first law of thermodynamics to define energy as the work an object can do, you must perform a perfectly reversible process, which is impossible in a finite time.) many experts emphasize understanding how energy behaves, specifically the conservation of energy, rather than trying to explain what energy "is". "The Feynman Lectures on Physics Vol I."(PDF). Diakses tanggal 3 Apr 2014.[pranala nonaktif permanen]
Society, National Geographic (2011-06-24). "biosphere". National Geographic Society (dalam bahasa Inggris). Diarsipkan dari asli tanggal 2020-10-28. Diakses tanggal 2020-10-08.
The Hamiltonian MIT OpenCourseWare website 18.013A Chapter 16.3 Accessed February 2007
Society, National Geographic (2011-06-24). "biosphere". National Geographic Society (dalam bahasa Inggris). Diarsipkan dari asli tanggal 2020-10-28. Diakses tanggal 2020-10-08.
