Wooden versus Steel Roller Coasters

• The mechanisms and scientific principles that keep the roller coaster on the track depend on the materials used in the construction of the coaster. The two primary types are wooden and steel-track; within each type there are various styles of coasters. The variants often relate to the position the riders, including models that allow riders to stand, sit, ride on top of the track or hang below it as well as coasters with rails on either side of the cars. The path of the track and the type of coaster dictates the mechanisms used to keep the coaster on the track.
  
  

Gravity, Inertia and Centripetal Force

• Physical principles are employed during the design and construction of roller coasters to ensure safety while offering seemingly dangerous jaunts along the track. Gravity plays a key role in providing the acceleration that is often the only source of propulsion once the roller coaster has been towed up the first incline. As the cars move over the track, gravity forces the cars downward to maintain contact with the track. Through turns, loops and other inversions, inertia -- force created by the velocity of the train -- holds the cars against the track. Even when the direction of the coaster is opposite the directional pull of gravity, centripetal force pulls the cars toward the outside of the loop, turn or other inverted shape and towards the track, counteracting gravity and pushing against the rails or the track itself.
  
  

Wheel Support

• While gravity and inertia cause the cars to be pressed against the track or rails, the wheels are responsible for maintaining smooth contact with the coaster's framework. As centripetal force pulls the cars in a direction opposite the turn, the wheels ride along the outer rails to keep the coaster on track. In the case of a steel coaster, the wheels are often above, below and on the outside of a tubular track to maintain contact between the track and the support system of the cars. For a right-hand turn on a steel coaster, the right outside wheel bears the burden of keeping a coaster in line; the same turn on a wooden coaster places the onus on the left inside wheel for support.
  
  

Braking

• Roller coasters are designed to function as expected through the course of the track with the speed and weight of the coaster's cars and passengers in mind. A coaster traveling at a given speed and bearing a given weight is calculated to result in a specific amount of force and momentum through each part of the track. In the event that the coaster is in danger of exceeding safe levels of force during any part of its course, brakes are used to slow the ride to a physically safe velocity. Another way to slow a coaster before a trouble spot is to add an incline; once again, gravity helps in slowing the car in lieu of brakes to keep the ride safely on the tracks.