The “Energy Alternatives'' topic depends much more to the realm of engineering sciences, than to the realm of “pure physics". We needed to start with introducing a number of important physical concepts (and we will once in a while return to “pure physics"), but now we will switch a mode that is much closer to an “engineer's approach".
We have to begin with classifying energy forms according to the ''sources they come from'', rather than their physical nature. And below there is a list of energies and their sources we will discuss throughout the present text. The items are listed in “chronological order'', beginning with the energies utilized by the most ancient civilizations, and ending with power sou\-rces that have only been most recently harnessed.
- Biological energy – the energy stored in our bodies. Humans started using this form of energy long before they became humans (for moving around, climbing trees, hunting, fighting…).
- Solar energy -same as above. E.g., to get warm after a chilly night.
- Chemical energy -that stored in the foods. Again, humans started taking advantage of this form long before they became humans.
- Thermal energy -that from fire. At the onset of civilization! It was the first form the use of which required human intellect!
- Animal energy: here we mean “biological energy'', but that stored in the bodies of domesticated animals, not our own bodies.
- Wind energy -first ever “hi-tech” devices built by humans used it! In sailing boats, wind mills, simple water pumps for irrigating fields.
- Hydro-energy – kinetic/potential energy of water in streams and artificial ponds – probably, started being used about the same time as wind energy. Ancient civilizations, e.g., Egyptians, used both!
Then, there was a long period with no significant progress in using new energy forms...
...Things started moving in fast pace only in the Second Millennium. The new forms that people employed then were:
- Chemical energy from “synthetic'', i.e. man-made carriers: gunpowder (a.k.a. “black powder''), first invented in China about 1000 years ago, was perhaps the first?
- Chemical energy from mined sources: (e.g., coal): widespread use begun in the 18th Century; then towards the end of the 18th Century came oil, and natural gas.
- Energy from heat engines -when coal became available; the first heat engine was built in England by Newcomen in early 1700-s then a far better machine was built about 50 years later by James Watt. When that happened, the “Industrial Revolution'' began!
- Electrical energy -19th Century; the proud 19th century people called their times The Century of Steam and Electricity.
- Geothermal energy -water from hot sources had been used for millennia by people who dwelled nearby, but an utilization at industrial scale began only in the early years of the 20th Century.
- Atomic (nuclear) energy – first used for not-so-nice purposes in 1945, for peaceful purposes a few years later.
- Mass, as discovered by A. Einstein, is also a form of energy (\)E=mc^2\)).
Is this list complete? Can you think of any other items?