The Roller Coaster's Twisted Story

G-Forces, weightlessness, loops, and corkscrew turns. Those are experiences only for jet pilots and astronauts, right? Not at all. All you have to do to experience the thrill of negative G's or a tight barrel roll is hop on a roller coaster.

Speed is what makes a roller coaster so exciting, says Alan Schilke, a roller-coaster designer for Arrow Dynamics Inc. in Clearfield, Utah. G-forces, air time, and inversions, like the loops and rolls that turn you upside down, also add to the thrill.

Roller coasters might give you some of the same sensations as a jet or rocket, but they don't operate on high-powered engines. Speed comes from starting the coaster cars from a great height. On the world's tallest coaster, Superman the Escape at Six Flags Magic Mountain, riders are towed to a height of 415 feet. The cars build speed to 100 m.p.h. on the long drop.

How about those weird feelings of either being pressed down into your seat or floating up out of it? What you're feeling is the effect of G-forces.

G-forces are measured in relation to gravity. When you're sitting still, gravity pulls you toward the earth with a force of 1 G. As you reach the bottom of a hill on a coaster and begin to move upward again, you're pushed down into your seat with a force of more than 1 G. You actually weigh more. This force also increases when the car accelerates, or builds up speed.

When the coaster goes over the top of a hill and you seem to float off your seat, that's the opposite effect. You're experiencing negative G's - where you weigh less than 1 G. It's called air time and it's the same feeling of weightlessness astronauts feel in space.

All of these effects are carefully planned when a roller coaster is designed. Mr. Schilke explains that any roller-coaster design is first tested on a computer that measures the forces acting on the cars and their occupants over every inch of the track.

"We keep the G-forces pushing you into the seat under 4 G's," he explains. "We keep the lateral, or sideways, forces under 1 G." It's one of the many ways coasters are designed for safety.

After the computer analysis, the track is built and then carefully tested. An accelerometer is mounted on a car while it goes over the course. This measures the forces acting on the car throughout the trip. Then comes one of the best parts of the job for a roller- coaster builder - test rides. Track builders and engineers take ride after ride to see for themselves if the coaster is a success. Once they're satisfied, it's open to the public.

The new coasters, with their complex corkscrews and loops, have come a long way from the original idea. The first such rides, called gravity rides, were built in Russia in the 1600s. In winter, wooden ramps up to 70 feet high were covered with water that froze into ice. Passengers would carry sleds up a ladder and then zoom down. They were called gravity rides because the sleds weren't powered, but relied on gravity to keep them moving.

The idea reached France in the 1800s, but the winters weren't cold enough to keep the ice frozen. So they ran the sleds on wooden rollers. That's why they're now called roller coasters!

The first gravity ride in the United States was in Pennsylvania in the 1870s, using an old mining railway. In the early 1900s, safety improved when inventor John Miller added undertrack wheels to the cars. Now each car has three sets of wheels. One set rides along the top of the track, another near the sides keeps the cars on course, and a third set of wheels under the tracks makes sure that the cars stay on the rails even when they're upside down.

By the 1920s, roller coasters were becoming popular in the US. The Depression of the 1930s and World War II in the early 1940s slowed down the production of roller coasters, but now there are over 350 coasters in the US.

The first American coasters were wood, but in the 1960s steel coasters began to appear. "Steelies" can be twisted into more-complex inversions and allow for cars that hang from an overhead track. But some people still prefer the original wooden coasters. They like the creaking of the wood as they zip around a turn. The creaking is a good sign: It means the wood is flexible and gives as the cars go over it.

So get your ticket and hop in. You're in for a screaming good time!

RECORD-SETTING ROLLER COASTERS

WOODEN COASTERS

Tallest: The Rattler at Six Flags Fiesta Texas in San Antonio, Texas, is 179 feet high.

Longest Drop: Mean Streak at Cedar Point in Sandusky, Ohio, drops 155 feet.

Steepest Drop: The Cyclone at Astroland in Brooklyn, N.Y., has a drop of 58.6 degrees.

Fastest: The American Eagle at Six Flags Great America in Gurnee, Ill., goes 66 m.p.h.

Longest Circuit: The Beast at Paramount's Kings Island in Kings Island, Ohio, travels 7,400 feet (1.39 miles).

Oldest (standing and operating):

The Rutschebahnen ('Scenic Railway') Mk. 2 was built at the Tivoli Gardens in Copenhagen, Denmark, in 1913. It opened to the public in 1914.

STEEL COASTERS

Tallest (complete circuit): The Fujiyama, at Fujikyu Highland Amusement Park in Japan, is 259 feet tall.

Longest Drop: Fujiyama, 230 feet.

Steepest Drop: (Tie) The Ultra Twister and Taz's Texas Tornado at Six Flags Astroworld in Houston, Texas. Both plunge down an 85-degree slope. (Straight down is 90 degrees.)

Fastest: Fujiyama, 81 m.p.h.

Longest Circuit: The Ultimate at Lightwater Valley Theme Park in Ripon, England, travels 7,542 feet (1.43 miles).

Most Inversions: Dragon Khan, in Port Aventura in Salou, Spain, turns riders upside-down eight times over the course of the ride.

Most Coasters: Cedar Point in Sandusky, Ohio, boasts 12.

Sources: World of Coasters; The Guinness Book of World Records

* For more info on roller coasters, check out: ecss.eng.iastate.edu/explorer/park/rc_main.htm