Automobiles are wheeled motor vehicles used primarily for transportation. They are of many different kinds, based on their shape and size, how they are powered, what they do, and whether they are built for track, air, underwater, or road. Almost all automobiles use an internal combustion engine to convert chemical energy into mechanical energy, which then turns the wheels of the car. The power that is used to move the automobile is measured in horsepower.

Modern life would seem inconceivable without a personal vehicle to take you to work, school, and all the other places that your everyday schedule takes you. Automobiles are so widely used that each year Americans alone drive more than three trillion miles. They have shaped urban design, government services like police, fire, and ambulance, and even the development of new businesses like gas stations, restaurants, hotels, and amusement parks.

The automobile was one of the most important forces for change in twentieth century America. It became the backbone of a consumer goods-oriented society and, by the 1920s, was the biggest customer of steel and petroleum products. Automobile production was also a leading job provider. In 1982 it generated one out of every six American jobs and was the major source of income for households with children.

Compared to walking or riding a bicycle, an automobile is faster and can carry more people. It is also convenient for travel over long distances and can reach places that are difficult to access with other forms of transport. However, it is expensive to operate and the environment suffers.

While the first automobiles were steam-powered, electric cars dominated the market in the early 1900s. But they burned fuel very quickly and were difficult to start. This led to the dominance of gasoline-powered automobiles, which could run for much longer on a single tank of fuel than steam or electric models. In the United States, the cheap raw materials and manufacturing methods introduced by Henry Ford helped make cars affordable to middle-class families.

Although automobiles have made modern life possible, they have also caused social problems. They contribute to air pollution and the depletion of world oil reserves. In addition, their driving styles are often reckless and dangerous. This is why many countries have laws to regulate the safety of automobiles.

The era of the annually restyled road cruiser ended with the imposition of federal standards for automotive safety, fuel efficiency, and emissions; with escalating gasoline prices following the oil shocks of 1973 and 1979; and with the penetration of both the U.S. and world markets, first by the German Volkswagen “Bug” (a modern Model T), then by Japanese fuel-efficient, functionally designed, well-built small cars. These factors signaled that the Automobile Age was melding into a new Age of Electronics. The automobile is still the most popular form of transportation, but it is no longer a progressive force for change in American society. That role has now been taken over by other technologies, including the electronic media and the computer.