How do roller coasters roll?

Answer 1

They roll on small wheels. :)

The cars are pulled (or pushed) to the top of the first hill on the track. Traditionally it is pulled to the top by a chain in the track that is driven by a motor on the ground.

The first hill is always the highest point on the track, thus the cars can "coast" down the rest of the track. If one of the later hills were higher than the first hill, then the cars would not be able to coast to the top of the higher hill. When ever the cars go down, they gain enough speed to coast to the top of the next hill.