What is meant by energy?

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.