<P> A roller coaster is a type of amusement ride that employs a form of elevated railroad track designed with tight turns, steep slopes, and sometimes inversions . People ride along the track in open cars, and the rides are often found in amusement parks and theme parks around the world . LaMarcus Adna Thompson obtained one of the first known patents for a roller coaster design in 1885, related to the Switchback Railway that opened a year earlier at Coney Island . The track in a coaster design does not necessarily have to be a complete circuit, as shuttle roller coasters demonstrate . Most roller coasters have multiple cars in which passengers sit and are restrained . Two or more cars hooked together are called a train . Some roller coasters, notably wild mouse roller coasters, run with single cars . </P> <P> The oldest roller coasters are believed to have originated from the so - called "Russian Mountains", specially constructed hills of ice located in the area that is now St. Petersburg . Built in the 17th century, the slides were built to a height of between 21 and 24 m (70 and 80 feet), had a 50 - degree drop, and were reinforced by wooden supports . Later, in 1784, Catherine the Great is said to have constructed a sledding hill in the gardens of her palace at Oranienbaum in St. Petersburg . The name Russian Mountains to designate a roller coaster is preserved in many languages (e.g. the Spanish montaña rusa), but the Russian term for roller coasters is американские горки ("amerikanskiye gorki"), meaning "American mountains ." </P>

What is the purpose of a roller coaster