ANYTHING THAT HAPPENS—from a pin-drop to an explosion—requires energy. Energy is the capacity for “doing work” (making something happen). Various forms ofenergy exist, including light, heat, sound, electrical, chemical, nuclear, kinetic, and potential energies. The Law of Conservation of Energy states that the total amount of energy in the universe is fixed—energy cannot be created or destroyed. It means that energy can only change from one form to another (energy transfer). For example, potential energy is energy that is “stored,” and can be used in the future. An object gains
potential energy when it is lifted; as the object is released, potential energy changes into the energy of motion (kinetic energy). During transference, some of the energy converts into heat. A combined heat and power station can put some of the otherwise “waste” heat to useful effect in local schools and
housing. Most of the Earth’s energy is provided by the Sun, in the form of electromagnetic radiation. Some of this energy transfers to plant and animal life, and ultimately to fossil fuels, where it is stored in chemical form. Our bodies obtain energy from the food we eat, while energy needed for other tasks, such as heating and transport, can be obtained by burning fossil fuels—or by harnessing natural forces like wind or moving water—to generate electricity. Another source is nuclear power, where energy is released by reactions in the nucleus of an atom. All energy is measured by the international
unit, the joule (J). As a guide, one joule is about equal to the amount of energy needed to lift an apple one meter.
