Energy. It’s a word you hear all the time, and everyone has some sense of what energy means. Moving objects have energy; energy is the ability to make things happen; energy is associated with heat and with electricity; we’re constantly told to conserve energy; living organisms need energy; and engineers harness energy to do useful things. Some scientists consider the law of conservation of energy to be the most important of all the laws of nature. But all that in due time—first we have to start with the basic ideas.
Just what is energy? The concept of energy has grown and changed with time, and it is not easy to define in a general way just what energy is. Rather than starting with a formal definition, we’re going to let the concept of energy expand slowly over the course of several chapters. Our goal is to understand the characteristics of energy, how energy is used, and how energy is transformed from one form into another. It’s a complex story, so we’ll take it step by step until all the pieces are in place.