In the context of physical sciences, several forms of energy have been defined. These include:
Some basic textbooks group all these forms of energy into two broad categories:[1] kinetic energy and potential energy. However, some forms of energy resist such easy classification, as is the case with light energy. Other familiar types of energy (such as heat in most circumstances) are a varying mix of both potential and kinetic energy.
However, the above set of the possible forms of energy is not a closed set. Whenever physical scientists discover that certain phenomenon appears to violate the law of energy conservation, new forms can be added, as is the case with dark energy.