IntroductionElectricity is generated by the use of energy. Before continuing it will be necessary to talk briefly about what energy is. Nowadays, the standard scientific definition of energy is the ability to do work, which means the ability to move an object against a resisting force (Boyle 2003). According to (Beggs 2009) a physicist or engineer will best describe energy in the form of an illustration. That is, let us consider a mass of 1 kg raised 1 m above the surface on which it was originally supported. Therefore, for the weight to have been lifted above the surface, a machine or someone must have performed some work. Simply, this means that in order to bring mass from a low level to a higher level, some work must have been put into the system. This work is basically the amount of energy put into the system. Therefore, in the raised position, the weight is at a higher energy level than when it is on the surface. This illustration forms the basis for the International System (SI) unit of energy, the "Joule". Electricity sources are available everywhere across the world with a wide range of resources available to generate electricity. These energy resources can be classified into two main categories which are renewable and non-renewable energy resources. With these resources, each of them can be used as a source to generate electricity, which is a very practical way to transfer energy from one place to another such as to industries or our homes. The non-renewable energy source can be further divided into two types: fossil fuels and nuclear fuel (electricity, 2012). Fossil fuels are the more popular of the two and are found in rocks on the Earth's surface....... middle of paper......006: Ecological Modeling | ScienceDirect.com. [ONLINE] Available at: http://www.sciencedirect.com/science/article/pii/S0304380010006113. [Accessed 6 March 2012]Fossil fuels and their impact on the environment. 2012. Fossil Fuels and Their Impact on the Environment. [ONLINE] Available at: http://www.essortment.com/fossil-fuel-its-impact-environment-57291.html. [Accessed March 6, 2012].Fossil Fuels: Environmental Impacts of Oil, Gasoline, Gas, and Coal and Future Use | Du La Bab - Now is the time. 2012. Fossil Fuels: Environmental Impacts of Oil, Gasoline, Gas, and Coal and Future Use | Du La Bab - Now is the time. [ONLINE] Available at: http://www.dulabab.com/energy-transportation/fossil-fuels/. [Accessed 06 March 2012]. 2012. . [ONLINE] Available at: http://www.ebb-eu.org/EBBpressreleases/ERA%20Study%20Impact%20of%20fossil%20fuels%20final%20report.pdf. [Accessed March 7 2012]