Norman Kendall, age 10, of Sparks, Nev., for his question:
HOW DOES AN ELECTRIC RAILROAD GET POWER?
You'll find electric railroad systems in many large cities. Often the cars run on elevated tracks or underground tunnels or tubes. Other times they run on open surfaces.
Power for electric railroad cars is usually generated in a power plant and passed along the railroad to separate traction motors used to drive the car wheels.
Current from the central powerhouse can be delivered to the cars in several ways. Some railroads have overhead lines above the track. A metal bar, or trolley pole, reaches up from the car or locomotive, slides along the overhead line, and collects and transmits power to the locomotive or car.
With this system, the bar is held against the wire by a pantograph, an accordionlike metal frame which can be raised or lowered and which carries the conductors. The current then travels through the conductors to the motors near the wheels, and drives the motors.
The engineer operates a controller in the cab of the locomotive or car. This device regulates the amount of power going into the traction motors and in this way regulates the speed. The United States has about 2,000 miles of these lines.
Other electric trains get their power from a "third rail" placed beside the track. The motors receive electricity from metal shoes that slide along this extra rail.
Many large locomotives now run on electric power. They have one or more traction motors geared to the driving axles. Electric locomotives weigh 110 to 364 tons. The largest can produce over 9,000 horsepower.
A typical electric locomotive in the United States weighs about 230 tons. It has 4,620 horsepower and a top speed of 100 miles an hour.
Diesel locomotives use diesel engines for their power. The engine drives generators that produce electricity. The generators drive electric motors geared to the wheels.
A man named Thomas Davenport in Brandon, Vt., built a first model of an electric railroad in 1835. Then in 1838, a man named Robert Davidson built an electric locomotive that ran on the Edinburgh Glasgow Railway. But the cost of producing electricity was too great for general use by railroads until the electric generator was invented.
The first locomotive that took its power from a generator by means of a third rail was shown at an exposition in Berlin, Germany, in 1879. A year later, in 1880, Thomas Edison invented an electric locomotive that ran on a special track in Menlo Park, N.J.
The first commercial electric street railway began operation in Lichterfelde, Germany, in 1881.
A man named Frank Sprague, who had worked with Edison, demonstrated the first practical electric motor for use in locomotives in 1884. Sprague inaugurated a small electric railway in, St. Joseph, Mo., in 1887, and later the same year he built the Union Passenger Railway in Richmond, Va. This was the first large electric railway system.
The first railroad main line electrification was on the Baltimore and Ohio tunnel district in Baltimore in 1895.