Energy is the power or capability to do a required piece of work. Everything that we do requires energy and nothing can be done without it. So much so that the existence human life is impossible without it. The energy being used by man at present may be divided into animate and inanimate energy. The energy that is derived from non-living matter namely coal, oil, natural gas and electricity is known as inanimate energy, while the animate energy^mostly comes from animals. The latest sources of energy available to man are atoms and the sun. A cursory look at the history of development of human civilisation will make it abundantly clear that energy forms the backbone of the world’s progress. The early man used the energy of his own body to perform all types of work. Use of animal energy for carrying load was a later innovation. So animals were domesticated to help man in his work. The inanimate sources of energy such as wind, water, steam etc. which came to be known to man afterwards, proved of great utility in doing difficult work for him and thus relieving him to devote his time and energy to higher and nobler things.
The invention of the steam engine in the eighteenth century marked the beginning of an unending age of newer inventions and discoveries which provided man with ample energy to attempt several things that were hardly thinkable before. The innumerable miracles that have been possible with the help of the new sources of energy have encouraged man to search for still newer sources of energy. Fossil fuel (coal, gas and oil) has been the most popular source of inanimate energy during the last one century. But there has been a marked shift in the relative use, utility and importance of the various sources of energy. During the last three decades wood and coal supplied about eighty per cent of the total commercial energy of the world.
But in the seventies the proportion of solid fuel has gone down to nearly half. Similarly there h as been a marked rise in the share of liquid fuel like oil and natural gas which has increased almost three times. This shift in the use of and preference for liquid fuel is primarily due to fact that it is easier to obtain energy from oil than from coal. The increrse in motor transport, dieselisation of railways, and naptha-based fertiliser plants has increased the world consumption of oil many times during the past decades. According to an estimate man has consumed more energy during the last three decades than in all his history before.