Roller Coasters
A roller coaster is a train powered by gravity. An initial store of potential energy is released dramatically during the ride.
A roller coaster's first hill, called the lift hill, is the highest point of the ride. As the coaster plunges down the first drop, its potential energy is converted into kinetic energy, the energy of motion. Later, some of this kinetic energy is converted back into potential energy as the coaster's speed decreases during a climb. Over the course of the ride, the coaster's total mechanical energy (potential plus kinetic energy) gradually decreases. This change occurs due to friction from the rails and the air, which causes the coaster's mechanical energy to be converted into heat. By the end of the ride, all the potential energy created on the lift hill has been lost as heat.