Between 1842and 1847, Julius Robert von Mayer, James Prescott Joule, and Hermann Ludwig Ferdinand von Helmholtz discovered and formulated the basics of what we refer to today as the law of conservation of energy. Energy cannot be created or destroyed; it can only be transformed from one form to another. Energy, in physics, the capacity for doing work. It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms. There are, moreover, heat and work - i.e., Energy in the process of transfer from one body to another. It takes energy to cook food, to drive to school, and to jump in the air different forms of Energy. Energy can take several various forms. The SI unit of energy/work is the joule (J), named for English physicist James Prescott Joule (1818 - 1889). Joule discovered the relationship between heat and mechanical work, which led to the development of the laws of thermodynamics.