News Story on Roller Coasters

Fun of coasters all in the physics

Science makes rides safe but gives us the thrill of 'danger'

Author: By Kelly Milner Halls

ATLANTA -- When Six Flags Over Georgia unveiled the Georgia Scorcher -- its rockin' new, 54-mph, 2.5-minute stand-up roller coaster -- this spring, one thing was on the minds of would-be riders. Fear.

"We all love to be afraid," says Six Flags spokeswoman Terrie Ward. "We love the anticipation that goes along with riding a roller coaster like the Scorcher."

What we love, says Atlanta psychologist Michael White, is the illusion of danger. "Because of safety regulations, we know roller coasters are not really dangerous," he says. "The perfect blend of fear and safety makes roller coasters especially appealing."

Maintaining that balance between scary and safe depends upon the magic of physics -- the science of matter and energy and how they interact.

That science is at work with every lift and loop, every camelback and corkscrew of the Scorcher. For each danger, there is a safeguard. And for every safeguard, there seems to be an element of risk.

Like most roller coasters, the Scorcher relies on that first, agonizing hill to propel the car through the rest of the ride. As the car inches up the incline, it stores energy to use on the way down. The scientific name for stored energy is "potential energy."

The coaster car saves energy produced by the motor that pulls the car to the top of the hill, says Jeff Templon, professor of nuclear physics at the University of Georgia. That potential energy will be used to power it through the rest of the ride.

The first hill on a roller coaster has to be perfect. Too much height and the coaster might descend too quickly and jump the track when it turns. Too little height, and it won't pick up enough speed to stay safely on the curves.

That built-up potential energy turns into kinetic energy as the coaster zooms down the first 101-foot hill. Kinetic energy is the energy of movement.

As each car descends, gravity hurls it down the coaster tracks.

The roller coaster picks up enough speed from heading down the first hill to push the car through the first loop. The kinetic energy used coming down the hill is converted back to potential energy as it climbs the first half of the loop, says Templon. When it descends the other side of the loop, the stored energy converts again to kinetic.

As long as designers make sure the rest of a track is lower than the first hill, the coaster will have enough energy to complete it, Templon says.

Even though George Lucas didn't invent centripetal force, you may have heard of it. When you go upside down on a coaster, it feels like there's a force pushing you into the seat, preventing you from falling out. Actually, it's only your seat, or, on this ride, the floor, pushing against you, Templon says.

Your body wants to move in a straight line, but the coaster track curves. The seats in the car follow the track and force your body into following that track as well. If the seat was not there pushing you around the loop, you would fall out.

When it comes to this two-humped bump, physics is required to prevent physical injury. The makers of restraints -- the straps and harnesses that hold bodies inside roller-coaster cars -- know their products will work. The humps can be especially rough because the shifts are so sudden. When the ride is heading up a hill, the seats are pushing your body up just as centripetal force does. But when the track drops suddenly, your body still may be moving up while the seats and your restraints are headed down.

Even though gravity never changes, it sometimes feels stronger. That feeling is measured in G-forces. When your body changes direction at high speeds, it will feel like gravity is pulling harder at you. Pilots feel G-forces when they flip or dive in their jets, and so will you when a roller coaster heads through a corkscrew loop. The Scorcher claims forces as high as four Gs (four times the ordinary pull of gravity on the human body) as well as zero Gs (that sense of floating or weightlessness).