In physics, the term<unk>  describes the amount of work which may be done by forces within a system.<unk>  changes within systems can be accomplished by adding or subtracting<unk>  from them, as<unk>  is a quantity which is conserved. Changes in the<unk>  of systems may also coincide with changes in the system's mass.<unk>  in a system may be transformed so that it resides in a different state.<unk>  in many states may be used to do a variety of physical work.<unk>  may be used in natural processes, machines, or to provide some service to society (such as heat, light, or motion). For example, an internal combustion engine converts the potential chemical<unk>  in gasoline and oxygen into heat, which is then transformed into the propulsive<unk>  (kinetic<unk>  that moves a vehicle. A solar cell converts solar radiation into electrical<unk>  that can then be used to light a bulb or power a computer.
Energy transformation
Drug metabolism
Signal transduction
Cell signaling
Carbohydrate metabolism
Heat transfer
Conservation of energy
Internal energy