The progress of man depends upon the use of energy in its various forms. Energy is classified into two types on the basis of sources.
1. Animate Energy.
If the energy is obtained from living organisms, the energy is called Animate Energy. In the beginning man basically lived on energy produced by his own muscles. Later he tamed animals and used the energy of their muscles.
Camel, horses, buffaloes, donkeys, etc. proved a good source of what is called energy from tamed animals, i.e., tamed energy. Man also gets energy from vegetation, i.e., wood etc.
2. Inanimate Energy.
The energy obtained from animals did not prove to be sufficient and trustworthy. Man found that the energy provided by inanimate sources was more useful and tremendous in amount. In the beginning, man used Wind as a source of energy. He created wind mills where propeller was moved by winds.
Sailing boats were powered by wind which pushed the sails attached to the boats and small ships. Water was used as a source of energy. The flowing water moved water wheels which helped him to grind his grains into flour, to extract oil from oil-seeds and to run small machines.
Presently Hydro-electricity is produced from the energy of flow of water. Coal brought about revolution in harnessing huge amounts of energy which is termed as thermal electricity. James Watt in 1776 used coal energy to run steam engine. This revolutionized industry and railway transport.
The chief sources of energy are:
(i) Human Power
(ii) Animal power
(iii) Wind Power
(iv) Fossil fuels (coal, oil, natural gas)
(v) Falling water
(vi) Nuclear energy
(vii) Solar energy
(viii) Tidal energy
(ix) Geothermal energy