If you­'re studying physics, there are few more exhilarating classrooms than a roller coaster. Roller coasters are driven almost entirely by basic inertial, gravitational and centripetal forces, all manipulated in the service of a great ride. Amusement parks keep upping the ante, building faster and more complex roller coasters, but the fundamental principles at work­ remain the same.

In this article, we'll examine the principles that keep coaster cars flying around on their tracks. We'll also look at the hardware that ke­eps everything running, as well as the forces that make the ride so much fun.

The amusement-park industry has experienced a coaster boom of sorts in the past 15 years or so. New catapult launching techniques, hanging-train designs and other technological developments have opened up a world of options for designers. In recent years, designers have introduced coasters that have you lyi­ng flat against the train car so you feel as if you are flying, and coasters that shoot you down long stretches of spiraled track. "Fourth dimension" coasters spin or rotate your seat as the ride twists, turns and free-falls. In this article, we'll also keep you in the loop on all the newest features and innovations.

At first glance, a roller coaster is something like a passenger train. It consists of a series of connected cars that move on tracks. But unlike a passenger train, a roller coaster has no engine or power source of its own. For most of the ride, the train is moved by gravity and momentum. To build up this momentum, you need to get the train to the top of the first hill (the lift hill) or give it a powerful launch.

­Chain Lift

The traditional lifting mechanism is a long length of chain (or chains) running up the hill under the track. The chain is fastened in a loop, which is wound around a ­gear at the top of the hill and another one at the bottom of the hill. The gear at the bottom of the hill is turned by a simple motor.

This turns the chain loop so that it continually moves up the hill like a long conveyer belt. The coaster cars grip onto the chain with several chain dogs, sturdy hinged hooks. When the train rolls to the bottom of the hill, the dogs catches onto the chain links. Once the chain dog is hooked, the chain simply pulls the train to the top of the hill. At the summit, the chain dog is released and the train starts its descent down the hill.

Catapult-launch Lift

In some newer coaster designs, a catapult launch sets the train in motion. There are several sorts of catapult launches, but they all basically do the same thing. Instead of dragging the train up a hill to build up potential energy, these systems start the train off by building up a good amount of kinetic energy in a short amount of time.

One popular catapult system is the linear-induction motor. A linear-induction motor