Roller coaster
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A Roller coaster is an amusement ride designed for amusement parks and modern theme parks. It consists of an elevated railway that carries a train through changes in speed and direction. The entertainment of the ride is provided by the velocity of the descent as well as features such as inverted loops, banked curves, and barrel rolls that produce g-forces, pressing down on the riders. "Negative g-forces" give the rider a sense of weightlessness at the peak of hills.
At first glance, connected roller coaster cars look much like a passenger train. But unlike a train, it is not powered by a motor, but by gravity and momentum. To build up the ride's momentum it must first climb the first hill (or lift hill) by use of a lifting mechanism called a chain lift. The lift usually consists of one or more chains running under the track. The chain is fastened in a loop and wound around a motor-powered gear at both ends of the hill. The motor turns the chain loop, propelling the coaster train up the hill like a conveyor belt. The cars are attached to the chain by several hinged hooks called chain dogs. In recent designs, the use of catapult-launching techniques is sometimes implemented.