”Energy can be neither created nor destroyed” is the principles of the conversation of energy or first law of thermo dynamics.
All living things depend on energy for survival; the modern civilization can continue to thrive only if existing sources of energy can be developed to meet the growing demand. Energy exist in many forms, from the energy locked up in the atoms of matter itself to the intense radiant heat emitted by the sun, and between these limits energy sources are available such as chemical energy of fuels and the potential energy of large water masses evaporated by the sun. The picture presented is one of humanity tapping into nature taking off energy at every level. Many sources of energy exist; many are known, some perhaps unknown; but when an energy source exists, means must first be found to transform the energy into a form convenient to our purpose.
The potential energy of large masses of water is converted into electrical energy as it passes through water turbines on its way from the mountain to the sea. The energy of combustion of coal is used to produce steam which passes through turbines to generate electrical energy; the energy of combustion of petroleum fuels is used to heat air which expands and pushed a piston in an internal combustion engine to develop mechanical work; uranium atoms are bombarded and nuclear energy released is used as heat to produce steam and generate electricity.
The machinery for such energy transformation has been developed over the last two centuries, mainly by practical engineering, followed closely, but sometimes more distantly by theoretical analysis and research. Even though refinements were made over the years, the fundamentals of these engines are the same. Thermodynamic is the science of the relationship between heat and work. The laws of thermodynamics are natural hypotheses based on observation of the world in which we live. It is observed that heat and work are two mutually convertible forms of energy, and this is the basis of the first law of thermodynamics.