ABSTRACT
Energy can be defined in a number of ways. In the broad sense, energy means the capacity of something-a person, an animal, or a physical system (machine)—to do work and produce change. It can be used to describe someone doing energetic things such as running, talking, and acting in a lively and vigorous way. It is used in science to describe how much potential a physical system has to change. It also is used in economics to describe the part of the market where energy itself is harnessed and sold to consumers. For our purposes in this text, we simply define energy as something that can do work.
