Automobiles are vehicles powered by internal-combustion engines that are used for transport. These four-wheeled vehicles are an essential component of modern life, providing a convenient means of travel for work and personal activities. The automobile has transformed many aspects of society and culture.
The earliest automobiles were rudimentary horse-drawn carriages with engines added. They evolved to become sophisticated systems of transportation, serving a wide variety of uses from commuting and recreational activity to the delivery of goods. The modern automobile has thousands of components, each with its own specific design function. These include the engine, fuel system, transmission, chassis, electrical system, cooling and lubrication systems, suspension, wheels and tires, and bodywork. The automobile must be constructed to meet the needs of its intended use and to comply with environmental and safety regulations.
Modern automobiles have become the dominant mode of transportation, accounting for more than three trillion miles (five billion kilometres) per year in the United States alone. It is difficult to imagine living without the convenience, flexibility and safety that the automobile provides. It has made possible a whole new way of life, making modern jobs in distant locations feasible and allowing for the creation of industries like gas stations and convenience stores.
In addition to their functional aspects, automobiles must be attractive and safe to drive. The design process is influenced by a variety of factors, including size and weight, aerodynamics (or ways to reduce air resistance), safety features, comfort levels, and appearance. The design of an automobile must also consider the needs of its intended users, such as whether it is required to travel quickly at high speeds or if it will be driven by children and elderly persons who are less able to cope with rapid acceleration.
The modern automobile is built from a variety of materials, including steel and aluminium. Composites, high-strength plastics, and carbon fiber are also used in some designs. Computer technology has greatly improved the efficiency and accuracy of design. For example, the use of CAD and CAM has enabled designers to create complex shapes with relative ease.
The simplest cars have an engine mounted on a chassis with the wheels and steering assembly attached to it. The chassis must be strong enough to support the weight of the car and flexible in order to withstand the shocks and tension caused by road conditions and driving. The engine may be gasoline, diesel, natural gas, hydrogen, or electric. In the intake stroke, the engine draws in air and fuel, compresses it to form a high-pressure jet, then ignites it with spark plugs to generate mechanical energy that propels the car. In the exhaust stroke, the engine blows the compressed air and fuel back out through the cylinder head. The mechanical energy is then converted to electricity and used to operate the motor, which in turn drives the wheels. The vehicle can also be powered by a battery or solar panels. Some cars are hybrids, combining an electric motor with an internal-combustion engine.