Automobiles are four-wheeled motor vehicles, usually powered by internal combustion engines that use gasoline (a liquid petroleum product) as fuel. The engine may be positioned to drive the front wheels or to drive the rear ones, or both. The engine is cooled by water, and its power is delivered to the wheels by a transmission system that may be controlled automatically or by manual gearshifts. Some automobiles use diesel engines that burn heavier fuel, but these are generally used for trucks and buses and a few family sedans.
The automobile revolutionized twentieth-century society. By the 1920s it was the backbone of a new consumer goods-oriented economy and provided one out of six jobs in America. Its demands made it the lifeblood of the oil industry and the chief customer of steel and other industrial products. It also accelerated the development of ancillary industries and technological changes that affected all other types of machines.
Today, most people can not imagine living without an automobile. Cars enable them to travel quickly and easily to work, school, shopping centers, social activities, and visits with friends and family. In addition, they can save time that would otherwise be spent traveling by foot, bus, or taxi.
As automobile technology has improved, many people have expressed concerns about the safety of modern cars, their nonfunctional styling, and their environmental impact. Some have also criticized the excessive consumption of petroleum, leading to a global shortage and concern about the future availability of the world’s oil supply.