There is a small but important difference between motors and engines. An engine is a device that converts chemical energy, in the form of gasoline, diesel or natural gas, to rotating mechanical energy. An electric motor is a device that converts electrical energy, from a power source, to rotating mechanical energy.

Many devices which operate on the principle of rotation, such as fans, pumps, conveyors, and power tools, rely predominantly on electric motors. So electric motors play an important role in many of today's highly productive industries, also contributing to the quality of life in offices and homes.

In the United States, 50 to 60 percent of all the energy sold by electric utilities is used to power electric motors, which actually generate more rotating mechanical energy than all passenger automobiles in the U.S. combined. An understanding of electric motors is vital for analyzing energy consumption and altering production in ways that save energy and money.