A locomotive is a specialized type of train car which is self-propelled, generating energy through the burning of fuel, the use of electricity, magnetic levitation, or other experimental methods. Locomotives can be used to push or pull train cars, and they can be seen on railroad tracks all over the world, propelling passengers and freight to various locations.
As a general rule, a locomotive is extremely powerful, because it must be capable of pulling or pushing a chain of train cars. Unlike locomotives, train cars lack a source of power, and their movement is totally dependent on the locomotive. Locomotives can pull long strings of heavy cars on both flat surfaces and grades, and they are literally the powerhouses for trains.
The earliest locomotives were developed in the first decade of the 1800s, and they were powered by steam. They were also fairly crude and low powered, although the steam engine was quickly refined during the 1800s to create powerful steam locomotives which could burn wood, coal, and other materials, depending on what was available. The development of the locomotive enabled the construction of railroads, which were a dominant method of land transportation for people and freight well through the first half of the twentieth century.
Although the classic image of a locomotive involves placement at the head of the train, a locomotive can also push from behind. Some railroads use what are known as push-pull operations, in which a locomotive pulls a train in one direction, and pushes it in the other. This eliminates the need for time consuming track switching, as the train can move easily in either direction.
Locomotives which are designed to pull freight trains tend to be the most muscular, since freight trains can get very long and extremely heavy. Passenger locomotives are more lightweight. Switchers or shunting locomotives are the smallest and most agile of the locomotive family, being used to move trains and train cars around in train yards. As a general rule, switchers are capable of immense amounts of traction, enabling them to quickly get heavy trains in motion and then using that energy to move them to their end destinations.
Several railroads continue to run classic steam locomotives, typically as a novelty. Many others use diesel and other fuels to power their locomotives, while electric locomotives are growing in popularity, along with locomotives which use more experimental technology. Light rail systems used for commuting often use self-powered cars which are known as motor coaches or motor cars; because each car runs under its own power, it is easy to move light rail trains around as needed, adjusting the number of cars and runs to meet demand.
