Work is defined as the product of an applied force and the distance through which the force acts. Work is measured in newton-meters, a metric unit called a joule. Power is work per unit of time. Power is measured in watts. One watt is 1 joule per second. Power is also measured in horsepower. One horsepower is 550 ft•lb/s.

Energy is defined as the ability to do work. An object that is elevated against gravity has a potential to do work. The object is said to have potential energy, or energy of position. Moving objects have the ability to do work on other objects because of their motion. The energyof motion is called kinetic energy.

Work is usually done against inertia, fundamental forces, friction, shape, or combinations of these. As a result, there is a gain of kinetic energy, potential energy, an increased temperature, or any combination of these. Energy comes in the forms of mechanical, chemical, radiant, electrical, or nuclear. Potential energy can be converted to kinetic and kinetic can be converted to potential. Any form of energy can be converted to any other form. Most technological devices are energy-form converters that do work for you. Energy flows into and out of the surroundings, but the amount of energy is always constant. The law of conservation of energy states that energy is never created or destroyed. Energy conversion always takes place through heating or working.

The basic energy sources today are the chemical fossil fuels (petroleum, natural gas, and coal), nuclear energy, and hydropower. Petroleum and natural gas were formed from organic material of plankton, tiny free-floating plants and animals. A barrel of petroleum is 42 U.S. gallons, but such a container does not actually exist. Coal formed from plants that were protected from consumption by falling into a swamp. The decayed plant material, peat, was changed into the various ranks of coal by pressure and heating over some period of time. Coal is a dirty fuel that contains impurities and sulfur. Controlling air pollution from burning coal is costly.Moving water and nuclear energy are used for the generation of electricity.

Summary of Equations