# Roller Coaster Designer

A roller coaster designer is part mechanical engineer and part magician. His or her job is to keep the riders of the coaster perfectly safe while at the same time scaring the daylights out of them. It is really not magic, of course. The designer's secret tools are physics and mathematics.

## Staying on Top

It may seem like magic when a roller coaster hangs upside down at the top of a loop, with nothing between it and the ground, but it is really nothing more than the principle of inertia . The physicist Galileo Galilei developed the concept of inertia in the sixteenth century. According to Galileo, objects that are in motion continue to move in the same direction and at the same speed unless an external force acts on them. If the forces acting on a roller coaster car could somehow switch off, at exactly the same moment when the car reached the top of a loop, the car would fly away, upside down, moving along a horizontal line. Now that would be magic!

In reality, both gravity and the pressure of the rails on the wheels push the car downward when it reaches the top of the loop. These forces, however, do not make the car crash straight down into the ground because of all the inertia they have to overcome. Instead, they push down just hard enough to deflect the car from its horizontal line and keep it on the tracks.

## Testing the Limits

Any deviation of a roller-coaster car from a straight-line, constant-speed path is called acceleration . When a car plunges downhill, riders experience acceleration downward and forward. When it screeches around a curve, the riders experience acceleration to the left or right. And when it finally (or too soon, depending on one's point of view) starts to brake, the riders experience acceleration in reverse.

Ever since Galileo's experiment of dropping two balls off the Leaning Tower of Pisa, physicists have realized that all falling bodies near Earth's surface accelerate at the same rate, regardless of their mass. This rate is about 32 feet per seconda quantity that often is denoted by the letter g. A force three times stronger than Earth's gravity will produce an acceleration of 3 g.

Because the human body has adapted to Earth's gravity, it cannot tolerate dramatically greater accelerations in any direction. For example, a normal person can tolerate 6 g of positive acceleration (the kind that mashes the rider down into the floor of the coaster) for only a few seconds before blacking out. A smart designer will not exceed those limits, and most roller coasters do not even come close.

The law of conservation of energytaught in any high-school physics courseenables the designer to work out how a change in height translates into a change in velocity. If friction and air resistance were ignored, the car's speed would be exactly proportional to the square root of the vertical drop. (Thus, a coaster needs to be built four times taller to double the speed.)

In reality, the designer cannot ignore friction and air resistance. A full car will be slowed down more by friction than a half-empty car; a car on a hot day will go faster because its wheels are better lubricated. For this reason, designers do not rely on calculations alone. They use an accelerometer to test out scale models, and even the full-scale ride, under every conceivable condition.

In a few high-tech rides, sensors monitor the speed of the car at every point. If the car is going too fast or too slow, the sensors can adjust the electric current running through the linear magnetic motor that drives it.

Part of the thrill of a roller coaster is the feeling of being out of control. There is no steering wheel to turn and no brake to push. But roller coaster riders hanging upside down in a car in the middle of a loop should relax: The engineers who designed the ride have used science and math to make sure that nothing bad will happen to the thrill seekers.

Dana Mackenzie

## Bibliography

Walker, Jearl. "Thinking about Physics while Scared to Death on a Falling Roller Coaster." Scientific American 249, no. 4 (1983): 162169.

### Internet Resources

Baine, Celeste. The Fantastical Engineer: A Thrillseeker's Guide to Careers in Theme Park Engineering. Farmerville, LA: Bonamy Publishing, 2000. <http://www.bonamypublishing.com>.

Clark, Alfred. "A Primer on Roller Coaster Dynamics." Part I: Rollercoaster! 9, no. 3-4 (1988): 3037. Part II: Rollercoaster! 10, no. 1 (1989): 3237. Part II: Rollercoaster! 10, no. 3 (1989): 2429. <http://www.me.rochester.edu/~clark/coast.html>.

Pescovitz, David. "Roller Coasters: Inventing the Scream Machine." Britannica Online Spotlights. <http://coasters.eb.com>.

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