Defining Energy

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In physics, energy is defined as the ability or potential to perform work or cause changes. As this definition implies, a system with energy need not do any work or cause a change, it only has to have the capacity to do so. A piece of wood sitting at rest some place does not do any work even though it has the capacity to do so (for example by burning it in a furnace to boil water to steam which then turns a turbine). The piece of wood therefore contains energy. In fact, all objects have energy by virtue of their own mass.


(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Meadows, D. H., et al., The Limit to Growth, Universe Books, 1972. Also see, The Limit to Growth: The 30-Year Update, Chelsea Green Publishing Company, 2004.

Diamond, J., Collapse: How Societies Choose to Fail or Succeed, Penguin Group, USA, 2004.

Cleveland, C. J., Encyclopedia of Energy, Elsevier Direct Science, 2004.

The International Journal of Energy, Science Direct Elsevier Publishing Company.

Applied Energy, Elsevier Publishing Company.

Journal of Energy Resource Technology, ASME International.

The Energy Journal, The quarterly journal of the IAEE’s Energy Education Foundation, (

External Links

Energy Citation Database, US Department of Energy (

Environmental Protection Agency (

US Department of Energy (

The NIST Reference on Constants, Units, and Uncertainty (

The Club of Rome (

The Sierra Club (