How Roller Coasters Work

In the beginning the cars are pulled to the top of the first hill. After that the coaster has to complete the ride on its own. You are not being moved around by a motor or pulled by a hitch. The conversion of  potential energy to Kinetic energy is what drives the roller coaster. All of the potential energy you need is present once the coaster ascends  the first hill. 

Once you're moving, different types of wheels help keep the ride smooth. Running wheels guide the coaster on the track, friction wheels control lateral motion and a final set of wheels keeps the coaster on the track even if it's upside down.