Roller coasters involve a balance of?

Roller coasters involve a balance of potential and kinetic energy. At the top of the hill, the roller coaster has maximum potential energy and zero kinetic energy. As it goes down the hill, its potential energy is converted into kinetic energy, which reaches its maximum at the bottom of the hill. The roller coaster then climbs the next hill, converting kinetic energy back into potential energy until it reaches the top. This process repeats throughout the ride.