# 1.18: What is Energy?

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##### Learning Objectives

By the end of this chapter, students will be able to

• List specific examples of non-renewable energy sources
• Explain what makes an energy source non-renewable
• Describe the main types of fossil fuels and how they formed
• Explain the environmental impacts associated with exploration, extraction and use of the different types of fossil fuels
• Explain nuclear energy, how it works, its benefits and risks

Watts Bar Nuclear Power Plant in East Tennessee. Image from Tennessee Valley Authority (Public Domain).

Energy is the ability of a system to do work. A system has done work if it has exerted a force on another system over some distance. When this happens, energy is transferred from one system to another. At least some of the energy is also transformed from one type to another during this process. One can keep track of how much energy transfers into or out of a system. There are two categories that all energy falls into: kinetic and potential. Kinetic energy refers to types of energy associated with motion (Figure $$\PageIndex{1}$$, top). For example, a rock rolling down a hill, the wind blowing through trees, water flowing over a dam, and a cyclist riding a bicycle are just a few examples of kinetic energy. Potential energy is energy possessed by an object or system due to its position in space relative to another object or system and forces between the two (Figure $$\PageIndex{1}$$, bottom). Examples include a rock poised at the top of a hill and water stored behind a dam. Some forms of energy are part kinetic and part potential energy. Chemical energy describes the potential of a chemical substance to undergo a chemical reaction and transform other chemical substances; hence it is a form of potential energy. Examples include energy stored in the food you eat and the gasoline that you put in your car.

Figure $$\PageIndex{1}$$: Examples kinetic (top) and potential (bottom) forms of energy. All images were obtained from Wikimedia commons (public domain).

Living organisms need energy to perform life-sustaining “work” in order to survive. For nearly all living systems on Earth, the sun is the ultimate source of that energy. Over time, we humans have developed an understanding of energy that has allowed us to harness it for uses well beyond basic survival. The development and evolution of human society is largely attributed to our relationship with energy. The first major advancement in human understanding of energy was the mastery of fire for cooking and heating. Modern civilization is especially dependent on energy and some of its most distinct characteristics such as population growth, environmental impact and climate change are all a consequence of energy use. We use energy to heat and light our homes; power our machinery; fuel our vehicles; produce plastics, pharmaceuticals, and synthetic fibers; and provide the comforts and conveniences to which we have grown accustomed in the industrial age. Societal complexity, affluence, and the gap between poor and rich peoples are all related to our level of energy consumption.