Automobiles, also known as cars or motorcars, are wheeled motor vehicles that are used for passenger transportation. They are powered by internal combustion engines fueled most often by gasoline (petrol), but sometimes by electricity or other fuels, and they usually have four wheels. Modern automobiles are conceived and designed with numerous standards and requirements that affect their safety, power, size and weight, aerodynamics or ways to reduce the friction of airflow over the vehicle, and appearance.
Cars allow their owners great freedom of movement over long distances and have changed the way societies are organized around them. However, a dependence on the automobile can encourage sprawl (straggling, low-density urban development) that degrades landscapes and creates traffic congestion. It can also increase the use of fossil fuels and contribute to global climate change.
The arrangement, choice and type of components in an automobile depends on its intended use. For example, a car designed for off-road driving requires durable systems that have high resistance to severe overloads and extremes of operating conditions. Similarly, a sports car built for speed requires a more powerful engine and enhanced handling and steering capabilities to optimize performance at higher speeds.
The invention of the Model T in 1910 and subsequent production techniques pioneered by Henry Ford lowered the cost of automobiles to levels affordable for middle-class Americans. As a result, automobiles became the dominant form of personal transport in the United States and many other industrialized countries.