But it can also be solved using conservation of mechanical energy. Assume an object is moving along the x-axis. The conservative internal force acting between parts of the system equals the negative derivative of the potential energy associated with that system. Microscopically all known forces are conservative. Therefore, microscopically, all energy is either kinetic or potential energy, and, if the system under consideration is the whole universe, the total energy of the universe is conserved.
Work is the conversion of one form of energy into another.
Macroscopically, there are forms of energy that can easily and completely be converted into other forms. We call these forms ordered energy . Gravitational potential energy is an example of ordered energy. The gravitational potential energy stored in a car on top of a hill is converted into kinetic energy as it rolls towards the bottom of the hill. Hydroelectric plants convert the gravitational potential energy stored in the water in a reservoir into electric energy.