The law of conservation of energy can be expressed as follows: the change of total energy of a system can only be equal to the amount of energy transmitted into or out of the system. Total energy is the sum of mechanical energy, thermal energy and any form of internal energy except thermal energy.
If a system is in an isolated environment, it is impossible for energy or mass to enter or leave the system. In this case, the law of conservation of energy is expressed as: "The total energy of an isolated system remains unchanged."
Extended data:
Different forms of energy can be transformed into each other through physical effects or chemical reactions. Corresponding to the various forms of material movement, energy also has various forms. In mechanical motion, it is manifested as the mechanical energy of an object or system as a whole, such as kinetic energy, potential energy and acoustic energy. In thermal phenomena, it is expressed as the internal energy of the system.
It is the sum of the kinetic energy of random motion of molecules in the system, the potential energy of intermolecular interaction and the energy in atoms and nuclei, but it does not include the mechanical energy of the whole system. For thermal motion energy, people know it through its mutual transformation with mechanical energy (see the first law of thermodynamics). There is also energy in various fields.
Mechanical energy, chemical energy, thermal energy, electric (magnetic) energy, radiant energy, nuclear energy and other different types of energy are transformed in various ways. For example, the most common electric energy (alternating current and batteries) can be converted from many other forms of energy, such as mechanical energy-electric energy, nuclear energy-thermal energy-mechanical energy-electric energy (nuclear power generation), chemical energy-electric energy (batteries) and so on.
Baidu Encyclopedia-Law of Conservation of Energy