Harnessing heat to work for us. Energy production always starts with a natural resource-such as sunlight, water, wind, coal, natural gas

Energy production always starts with a natural resource-such as sunlight, water, wind, coal, natural gas, oil, or uranium-which goes through processes that convert the energy into other forms. Technological progress has been marked by the development of ways to capture, manipulate, and control large amounts of energy for useful purposes. Hundreds of technologies have been invented to carry out energy conversion processes, including steam engines (boilers), turbine generators, internal-combustion engines, batteries, photovoltaic cells, and many other devices.

Here is a brief look at how two of these inventions-the internal-combustion engine and the turbine generator-do their work.

In an internal-combustion engine, an electrical spark from the spark plug ignites gasoline, causing combustion. Combustion makes molecules move faster, causing the gas to expand. The expanding thermal energy is converted to mechanical energy in the movement of the pistons, cylinder, and crank shaft, which turns the wheels. The engine walls must be cooled or the engine will melt. Oil and water from the radiator cool the walls of the cylinder. Air from the fan cools the water in the radiator, releasing heat energy into the environment.

In the last 100 years, the automobile has vastly increased our mobility and reduced the time and effort required to transport people and materials.

Most power plants have enormous boilers that burn fuel-usually coal, oil, or natural gas- to make heat. The heat is applied to water to generate steam, which is then compressed. Compressed steam has more power than hot water. The steam travels to giant turbines and forces them to spin. The turbine shaft is attached to a turbine generator, which is a giant magnet inside a stationary ring, wrapped with wire. The shaft turns the magnet, creating a magnetic field, which produces an electrical current in the wire.

Hydroelectric, nuclear, coal, and natural gas power plants all spin turbines to generate electricity.

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