Energy comes to us in many forms. Usually, though, it does not come in the correct form to produce power for our transportation. A transportation device, such as a car, typically needs different types of power. For example, mechanical energy is needed to push a car forward. Electrical energy is required to operate its headlights.

Gasoline and diesel engines are examples of energy converters. Energy converters are designed to accomplish one purpose: to convert energy into useful work. Engines convert the energy stored in fuels into power or mechanical energy, which is used to operate the vehicle.

If you look under the hood of a car or a truck, you will see a heat engine. A heat engine is a device that uses heat energy to do work. The engine does work by changing heat energy into motion.

Figure 1 Heat engine Heat engines use thermal energy to do useful work.