What is the science behind roller coasters?

The science behind roller coasters is pretty simple. They actually go waaay back in history. Now at days, people use steel or metal to build it. They bolt it together and viola! A Roller Coaster! But one problem, the train that goes on it! The train that goes on it is a magnet and has wheels. The weight of the train and the chains on the roller coaster move it. Happy Searching! :)