The word energy is commonly used in the news media and in everyday conversations. Although the word has a precise scientific definition, it has come to be used in a much broader sense. In physics, energy is defined as the capacity for doing work or overcoming resistance.

There are two types of energy: potential, or stored energy, and kinetic, or energy in motion.

Potential energy is stored, or latent. Energy can be stored in many ways: a gallon of gasoline or a gallon of oil contains stored energy; a lake in the mountains contains stored energy. When we talk about oil, coal, wood, or gas, we are talking about stored energy.

Kinetic energy is actual energy in motion. Electricity, moving water, wind, and solar radiation are examples of kinetic energy.

Energy can be changed from one type to another. For example, a car being driven up a hill is manifesting kinetic energy. When it sits on the top of the hill, it has potential energy. If it is then allowed to roll back down the hill, the potential energy changes again into kinetic.