Elevators use two different sets of doors: doors on the cars and doors opening into the elevator shaft. The doors on the cars are operated by an electric motor, which in turn is operated by the elevator computer. In a relatively short period of time, elevators have become essential to urban life.
As people continueto erect monumental skyscrapers and make small buildings handicap-accessible, elevators will become an even more pervasive element in society. It is truly one of the most important — and useful — machines ofthe modern era