In physics, energy is a fundamental quantity that every physical system possesses. Energy of physical system in a certain given state is defined as the amount of work (W) needed to change the state of the system from some initial position to a specific or final position. Energy is found in different forms: Kinetic energy: the energy of moving objects; Thermal energy: the energy associated with heat; Sound energy: the energy of compression waves; Electrical energy: the energy of moving charged particles; Potential Energy: the energy that an object has due to position; also known as stored energy; Chemical energy: the stored energy of chemical substances; Nuclear energy: the stored energy of the atomic nucleus and Radiant energy: the energy of electromagnetic waves, including light. Energy can be readily transformed from one form into another; for instance, using a battery to power an electrical heater converts chemical energy into electrical energy, which is then converted into thermal energy. Also, energy could be transformed in matter and vice versa as the theory of relativity states.

This category is for educational and general interest websites related to energy, its role in the physical systems, and its different forms .

Only comprehensive websites intended, targeted, or appropriate for people under the age of 18 will be listed here.

Websites about specific forms of energy should be sent to the most appropriate subcategory, for example: nuclear energy should be submitted to Atoms,_Nuclei_and_Particles .

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