Stunts in motion.

If you saw True Lies, Virtuosity, Independence Day, or Clueless, you've seen LaFaye Baker in action. Most people think her job is dangerous. But "stunt people are very concerned about safety," she says.

How did she stay safe in the hot stunt shown here? Her inner clothes were made of Nomex, a fireproof material. The night before the shoot, she soaked the clothes in a fireproof gel. After suiting up, she also rubbed the gel on her exposed skin.

To get something to burn, movie technicians coated the back of Baker's outer clothes with a highly flammable glue. They covered the rest of her suit with another inflammable solution. When they lit the suit, only the areas with the glue burned.

"As soon as I felt the slightest bit of heat, I lay down," Baker told us. "That's the signal for put me out.'" And they did, with a fire extinguisher!

Having survived that ordeal, Baker now takes the ultimate risk: rating the stunts -- and revealing the science -- in four popular movies. Turn the page for her top-trick picks.

The secret Russian hideout in GoldenEye was located at the base of an 800-foot dam. To get inside silently, Wayne Michaels (Pierce Brosnan's stunt double), plunged 229 meters (750 feet) in this world-record bungee jump!

As Michaels fell, his velocity increased until it reached 200 kilometers (124 miles) per hour. That speed is called terminal velocity -- the fastest a falling body can go. At terminal velocity, the force of air resistance -- friction from air pushing up on a falling object-is equal to the force of gravity, Earth's downward pull.

The bungee also helped slow Michaels' motion -- as soon as his weight pulled down on the cord and made it start to stretch. The longer the bungee stretched, the greater its elastic force -- the force that makes stretchy things snap back. (Think of a bungee as a giant rubber band.) The upward pun of the bungee worked against the downward pun of gravity.

When the bungee reached its longest stretch, its elastic force was more powerful than gravity. So the cord snapped Michaels back up almost 60 meters (200 feet). Michaels bounced up and down, less and less each time, until finally, he stopped -- at a safe distance above the ground.

This is no stunt double. It's Jackie Chan himself, snowboarding off a 30-foot slope after a high-speed chase. Chan knew he could fly out far enough to catch the copter: He just used the laws of motion!

Chan flew off the slope in a horizontal direction. According to Newton's first law of motion (also called the law of inertia), he would continue moving horizontally until a force made him stop or change direction.

The force of gravity, Earth's downward pull, would eventually change Chan's route and pull him toward the ground. But gravity doesn't affect the horizontal speed of a moving object. Chan knew the faster he flew off the slope, the farther he'd go before gravity pulled him down.

So he snowboarded off the slope at top speed, and was able to reach the 'copter before falling to the ground. Luckily, his aim was excellent!

In the movie Speed, Brian Smrz (Keanu Reeves' stunt double) had to jump from a speeding car onto a speeding bus. In the stunt, both the bus and the car were really going about 72 kph (45 mph). But Smrz said it wouldn't have mattered if they were going double that speed -- he still could've made the leap.

The important thing was that the car and bus be moving at the exact same speed. Why? Newton's first law of motion again -- moving objects keep moving at a constant speed in one direction unless a force "interferes."

Before the leap, Smrz lined himself up with the door of the bus. At that moment, Smrz's body was moving forward at 72 kph (45 mph), the same speed as the car. When he jumped, no force -- neither gravity nor air resistance -- had enough effect to interfere with that motion. So, as he leaped out toward the bus, his body also kept moving forward at 72 kph.

Because the bus was moving at the same speed, Smrz and the bus stayed in line with each other during the leap. So Smrz didn't "miss the bus!"

This stunt looks tough, but anyone could do it. That's because the hard part was faked with a computer!

First, the helicopter explosion was filmed in a movie studio. Then Tom Cruise was filmed separately in front of a green screen. A green screen is exactly what it sounds like -- a large, blight green screen. Cruise swung in front of the screen on a cable hanging from the ceiling. As he swung, he thrashed his body to create an "explosive" effect.

After filming, visual-effects experts used a computer to remove the green background. That left a "cutout" of Cruise. The experts then combined the cutout with a shot of the explosion, and made an instant stunt!

As technology gets better and cheaper, more movie "stunts" are made with visual effects. Next time you see an unbelievable-looking stunt, check for a thin black line around the actor. That's a sure sign the effect was computer-generated!

SAVE THE STUNT CHIP!

How do stuntpeople survive high falls? Try this experiment with a "stunt chip!"

WHAT YOU NEED

3 unbroken Pringles[R] Potato Crisps * 2 measuring sticks * random materials to save your chip (tissues, cotton balls, bubble wrap, tissue paper, plastic bags, plastic wrap, rubber bands, etc.)

WHAT TO DO

1. Hold a chip horizontally 15 cm (6 in.) above a hard floor.

2. Drop the chip. If it doesn't break, hold it 5 cm (2 in.) higher and drop again.

3. Repeat Step 2 until the chip breaks. Record this height.

4. Blow a zip-close bag half full of air and seal it.

5. Put this "air bag" on the floor and repeat Steps 2-5 over the bag. Record your observations.

6. For your chip's next stunt, it must fall from a height of 2 m (6 ft.) and land on a hard floor. Invent a device that allows your chip to do the stunt without breaking. Make and test your invention using your three remaining chips.

CONCLUSION:

How much higher could your chip fall when you used an air bag? What's the relationship between fall height and falling speed? Use the results from your experiment to explain why a faster-moving body hits the ground with more force than a slower-moving one. Then, explain how your design helped your chip land unbroken.

DON'T STOP NOW!

What's the highest fall your stunt chip can survive using your device? Test to find out!