Energy is described as the amount of work that can be done by a force. There are various forms of energy such as kinetic energy which is the energy of motion, potential energy which is stored energy like that in a battery or a tank of gas, thermal energy, electromagnetic energy, sound energy and light energy. There is also gravitational and elastic energy. Energy cannot be created or destroyed, however, it can change forms. For example, when a firecracker is ignited, potential energy is changed to light, heat and sound energy. If a piece of wood which contains potential energy is burned by combustion, light energy is released as well as heat energy. Because the heat energy is dissipated into the atmosphere, it can no longer do work. The total energy in a system remains the same, although it may be transformed from one type to another. This is explained by the Law of Conservation of Energy.