About roller coaster

The Scenic Railway at Luna Park (Melbourne, Australia), the world's oldest continually-operating rollercoaster, built in 1912.

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/6/65/Luna_Park_Melbourne_scenic_railway.jpg/180px-Luna_Park_Melbourne_scenic_railway.jpg

The roller coaster is a popular amusement ride developed for amusement parks and modern theme parks. In essence a specialized railroad system, a roller coaster consists of a track that rises in designed patterns, sometimes with one or more inversions (such as loops) that turn the rider briefly upside down. The track does not necessarily have to be a complete circuit, as shuttle roller coasters exhibit. Most roller coasters have multiple cars in which passengers sit and are restrained into. An entire set of cars hooked together is called a train. Some roller coasters, notably Wild Mouse roller coasters, run with single cars.
The cars on a typical roller coaster are not self-powered. Instead, a standard full circuit roller coaster is pulled up with a chain or cable along the lift hill to the first peak of the coaster track. The potential energy accumulated by the rise in height is transferred to kinetic energy as the cars race down the first downward slope. Kinetic energy is then converted back into potential energy as the train moves up again to the second peak. This hill is necessarily lower, as some mechanical energy is lost to friction.
A properly designed roller coaster under good conditions will have enough kinetic, or moving, energy to complete the entire course, at the end of which brakes bring the train to a complete stop and it is pushed into the station. Most large roller coasters have the ability to run two or more trains at once. One common pattern, used on rides with two trains, is to do the following: hold train #1 (which has just finished the ride) right outside the station, release train #2 (which has loaded while #1 was running), and then allow #1 into the station to unload safely.
Many safety systems are implemented within roller coaster systems. The key to the mechanical fail safes is the control of the roller coaster's operating computers: programmable logic controllers (often called PLCs).
Today, there are two main types of roller coaster:
- Steel roller coasters
- Wooden roller coasters (also known amongst enthusiasts as 'Woodies')
Steel coasters are known for their smooth ride and often convoluted shapes that frequently turn riders upside-down via inversions. Wooden coasters are typically renowned by enthusiasts for their rougher ride and "air time" produced by negative G-forces when the train reaches the top of hills along the ride.
Rank　　　　　　Speed
Roller Coaster　　Amusement Park
Location　　　　　　　　　　　　Opened

1st　　　　　　　128 mph
Kingda Ka　　　　Six Flags Great Adventure
Jackson, New Jersey 08527 USA　　5/21/2005

2nd　　　　　　　120 mph
Top Thrill Dragster　Cedar Point
Sandusky, Ohio 44870 USA　　　　5/4/2003

3rd　　　　　　　106.9 mph
Dodonpa　　　　　　Fuji-Q Highland
Fujiyoshida, Yamanashi Japan　　　12/21/2001

4th　　　　　　　100 mph
Superman The Escape　Six Flags Magic Mountain
Valencia, California 91355 USA　　　3/15/1997
Tower of Terror　　　　Dreamworld
Coomera, Queensland 4209 Australia　1997

5th　　　　　　　95 mph
Steel Dragon 2000　　　Nagashima Spa Land
Nagashima, Kuwana Mie 511-1135 Japan　9/3/2006
I hope this can help your understanding.

Roller coaster is build to the pleasure for human being, it can be as fast as human can endure. The limit is not about technology, it is about HUMAN. Pleasure is the only reason to be existed.