First off there are three launch systems; 1) the chain lift, 2) the catapult and 3) wheel launch. The traditional launching system is called a chain lift. The chain lift method consists of chain dogs (hooks) that hook onto a long length of chain or chains that are used to lift the coaster to its highest peak. As the coaster goes up the lift hill, it is building potential energy that will be turned into kinetic energy on the way back down. Another method of launch is the catapult launch that builds up an abundance of potential energy without using a lift hill to build potential energy. There are many types of catapult launches. An example of a catapult launch would be LIM (Linear Induction Motors). The LIM launch system uses dozens of electro magnets to build two magnetic fields. One dozen on the coaster and one dozen on the track. Then a motor pulls the dozen electromagnets on the track that pull the coaster behind it. One more launch system uses dozens of rotating wheels that grip onto the top or bottom of the coaster and push it forward. (HowStuffWorks.com )
When you ride a roller coaster you probably don't think about it but there are physics that keep you going. The first physics concept you usually encounter is potential energy. When you go up the first lift hill or are waiting for launch, even though you may not know it, the roller coaster you are seated in