Automobiles are self-propelled vehicles that have four wheels and an internal combustion engine fueled most often by gasoline. They are one of the most universal of modern technologies, and are manufactured by a large industry with a global reach. The automobile is the most common form of vehicle, with over 73 million cars in 2017 worldwide.
The automobile has a long history, with some of its early innovations having been preceded by horse-drawn carriages and steam-powered road vehicles. These earlier forms of self-propelled vehicles were slower than cars and often required a person to stand in front of the vehicle, carrying a red flag or a red lantern.
Cars use water-cooled, piston-type, internal-combustion engines; these may be mounted in the front of the vehicle and have power transmitted to all four wheels, or they may be carried in the back of the vehicle. The latter arrangement, while wasting space, is preferred by some manufacturers, as it provides good weight distribution and makes for more efficient use of fuel.
There are several different types of engines used in the automobile, including: gas, diesel, and electric. Gasoline engines are most common, but some manufacturers also produce diesel cars.
Gasoline engines are generally less efficient than those fueled by diesel; they are often more expensive, but also more durable. Some gasoline engines are air-cooled, and others have liquid cooling.
Many cars today have friction brakes on all four wheels, to slow or stop the vehicle in response to a force applied by the driver. These are used to prevent collisions with other vehicles, pedestrians, and obstacles such as trees or rocks.
A number of environmental problems have been associated with the use of automobiles, including air pollution and the buildup of pollutants such as carbon monoxide, hydrocarbons, and smog in the atmosphere. These pollutants are a major source of respiratory illnesses and other health issues, and they pose a serious threat to the environment.
In addition to the problems mentioned above, the automotive industry has caused significant damage to the environment by producing large amounts of toxic wastes. These wastes are deposited in landfills, incinerators, and on roadways, and they pollute the air and are sometimes washed into streams.
Some of these wastes, such as motor oil and brake fluid, can be hazardous to human health. They can cause kidney and liver disease, asthma, and gastrointestinal problems.
The automotive industry is a source of many industrial and commercial pollutants, such as carbon dioxide, nitrogen oxides, and particulates. These pollutants can cause serious health effects, including heart attacks and lung cancers.
Some of these pollutants are emitted into the air when the vehicle is moving, while others are produced by the exhausts of the engine. Some of the emissions from automobiles can cause serious damage to the ozone layer, and they can lead to acid rain. They can also contribute to soil erosion and flooding, which can impact agriculture, livestock, and the tourism industry.