Scream machines.

Though coasters couldn't get scarier? An SW thrill-seeker takes you on a new ride into terror--thanks to technology (and physics).

Prepare for the most chilling adventure of your life," booms the bass voice on the sound system. Locked into my seat, I await my fate on "Batman and Robin: The Chiller"--the newest roller coaster at Six Flags Great Adventure in Jackson, New Jersey. From a distance, the coaster looks like a snarled mass of metal. But from my seat all I see is a blue steel track stretching flat ahead, snaking through a dim tunnel--then up. I mean straight up.

I'm tense. Very tense. The guy sitting next to me, however, couldn't be calmer. It figures--he's Larry Chickola, the park's chief engineer.

"Takeoff in 3 ..." A supersonic noise starts to rev. "... 2 ..." The sound peaks with a space-age blast. "... 1!" The Chiller hurtles from 0 to 113 km/h (0-70 mph) in four seconds as we streak right toward the vertical rise. Is that my heart in my throat? I'm no roller-coaster wimp, but this boost-off is extreme! Obviously The Chiller isn't your average coaster, given its intense launch system and clever design. But no matter how terrifying the ride, the real forces behind all scream machines are pure physics.

SO LONG, LIFT HILL

When I boarded The Chiller, I expected a click-clacking chain to haul my car up a lift hill, a roller coaster's first peak. Ancient history. There's no lift hill in sight on The Chiller, on "The Blast Coaster" at Kings Dominion in Richmond, Virginia, or on "Mr. Freeze" at Six Flags in St. Louis.

Instead, these new coasters boast motors that launch you horizontally toward the first hill--which has no chain at all. Both launch systems and lift hills lend coaster cars the one thing they need to complete the ride: energy.

A towering lift hill "fuels" the train with potential energy, or energy that can be used later. "The lift hill gives the car the potential to go, say, 65 miles per hour at the bottom of that hill," Chickola says.

After the car crests on the summit, the downward pull of gravity takes over, and the train plunges down the track. On the descent, potential energy converts to kinetic energy, or energy of motion (see diagram).

Launch systems, on the other hand, use motors to kick off the train with kinetic energy right from the start. Awaiting takeoff on The Chiller, I spotted the energy source: 188 rectangular "magnet motors" installed along the station track (see p. 11).

Thanks to launch systems, coaster designers don't need to rely on gravity alone to propel trains from loop to loop. If a designer wants the train to speed up midride, he or she can add motors anywhere along the track. "I don't think all new coasters will have launch systems," says Chickola. "But crew park's going to want to have one ride that does."

DESIGNED TO THRILL

Other new coasters get their thrill from radical design as well as technology. Take "Dueling Dragons," a coaster at Universal Studios Islands of Adventure in Orlando, Florida (scheduled to open next summer). It touts two separate tracks with two dragon-shaped cars that rush furiously toward one another. This coaster gives "scream machines" new meaning--it creates near-collisions! Riders miss each other by only 30 cm (12 in.).

To make sure the near-crashes are timed perfectly, Dueling Dragons' designers had to contend with a major force: friction. Two factors cause friction on a coaster: the rubbing of the car's wheels against the track, and the rubbing of air molecules (called air resistance) against the car's surface as it whooshes along. As a train's energy converts to friction, its speed slows until little energy is left at the end of the ride. When the car lurches into the station, brakes add extra friction to stop it.

But the heavier the car, the harder it is for air resistance to check its speed. That means cars with heavier riders coast slightly faster than lighter cars. "If a lighter car is a couple of seconds late heading into a near-collision, the thrill is lost," says Joe Casey, an engineer at Universal Studios.

So builders are adding a computer that calculates the cars' weight and the amount of friction to expect. The computer will "decide" which car should shoot out of the station first, and when. That way the cars "almost crash" at exactly the same time. Sound like fun?

ENTER THE G-FORCE

Coasters aren't the only death-defying rides to debut this year. "Power Tower" at Cedar Point in Sandusky, Ohio, has fired riders up and down four steel towers since spring '98. At 91 m (300 ft), the ride is the world's tallest tower ride!

Imagine you just strapped yourself--legs dangling--into a seat in one of Power Tower's carts. Suddenly cables attached to a motor yank up your cart, shooting you sky-high at 80 km/h (50 mph). As you accelerate (gain speed) up the tower, a mighty force thrusts you down, flattening you like a pancake in your seat. That force of acceleration is called a G-force.

Earth's gravity tugs at you with a force of 1G. But Power Tower's 4-G pull is four times the force of gravity--more forceful than a space-shuttle blastoff!

As your cart careens to Power Tower's summit, you halt for a moment. During the pause you'll feel the effect of inertia--your body's resistance to a change of speed or direction. Like any moving object, your body moves in a straight line until forced to slow down or curve. When the cart slows down atop the tower, your body still moves up for a moment--even after the cart starts to head back down. So you feel weightless--a negative G-force--before you fall.

... AND BACK AGAIN

Forty-five seconds after the jaw-clenching Chiller launch, my car screeches to a halt back in the station. "That was an adrenaline rush!" yelps a dazed passenger. I have to agree as I stagger out of my seat. Who knew physics could be so thrilling--and chilling?

RELATED ARTICLE: hands on science

BATMAN & ROBIN: THE CHILLER

Six Flags Great Adventure Jackson, NJ Max height: 61 m (200 ft) Max speed: 113 km/h (70 mph) Max G-force: 4.5 G's Ride time: 45 seconds Thrilling fact: Midway through the ride, the train reverses and passengers retrace the track backwards!

POWER TOWER

Cedar Point Sandusky, OH Max height: 91 m (300 ft) Max speed: 80 km/h (50 mph) Max G-force: 4 G's Ride time: 45 seconds Thrilling fact: The idea to build Power Tower popped into the designer's head as he played with his nine children, tossing them in the air!

Roller-coaster Physics

On a lift-hill coaster, a motorized chain pulls the train up the first hill.

A launch-system coaster blasts riders towards the first hill. Motors give the train the kinetic energy it needs to make it over the hill.

With either coaster, you acceleration is highest at this point. So you'd feel the most G-force here.

As the train rounds hill, your body's inertia--the tendency to move in a straight line--keeps you moving up for a moment.

Inertia keeps your body moving down in your seat as you bottom into the valley. That makes you feel extra-heavy.

The train's inertia and fast speed press the train into the track around a loop. If the train stopped, underside safety wheels would prevent the train from falling off the track.

Gradually, all the train's energy converts into friction, which slows the train. Brakes add more friction to drain remaining energy. The train stops, Whew!

DUELING DRAGONS

Universal Studios Islands of Adventure

Orlando, FL Max height: 38 m (125 ft) Max speed: 97 km/h (60 mph) Max G-force: 4 G's Ride time: 3 minutes Thrilling fact: Dueling Dragons is the world's first coaster designed so riders experience near-crashes. Plus, you sit below the track so your feet hang!

HOW MAGNETS MOVE THE CHILLER

1 The motors's two halves each create a stone magnetic field, which moves forward along the motor.

2 A metal fin on each car slides through the gap. The motor's magnetic field creates a magnetic field in the fin.

3 As the motor's field moves forward, it attracts the fin's field. The fin attempts to "catch up" to the motor's field.

4 The train takes off!

hands on science

Use the FORCE(S)

Want to see a coaster's physical forces up close and personal? Try this:

WHAT YOU NEED:

plastic cup * 1-m (39-in.)-long piece of string * tape * penny

WHAT TO DO:

1. Tape the string to a cup as shown.

2. Drop the penny in the cup.

3. Let the string hang from one finger like pendulum. Keeping your finger steady, lift the cup as shown. (The string should be taut.)

Imagine the cup is a coaster car. What does lifting the cup represent? (Hint: It's a certain point on the track.)

Let go of the cup, but keep both hands steady. Does the cup swing all the way back to your hand? Why or why not? How did your cup's energy change during this experiment?

4. Now hold the end of the string with one hand. Swing the cup in a vertical (up and down) circle in front of you. Does the penny stay in the cup? (Even when the cup is upside down?) Use what you learned about inertia to explain your results. What happens when you slow down your swing? How is your cup like a coaster car rounding a loop?

5. Hold the middle of the string instead. Swing the cup seem to move faster or slower than in step 4? Would a coaster car have an easier time making it around a small loop or a large loop? Why?

DON'T STOP NOW:

Pour a half-cup of water into the cup. Repeat steps 4-5...outside.