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In the amusem­ent park industry, the  is king. But during the hot summer months, these classic attractions get some tough competition from inflatable slide. In the past 30 years, the world of  slides has exploded. They've transformed from­ simple poolside slopes to intricate attractions that dominate entire parks. According to the World Waterpark Association, there are more than 1,000 water parks in North America, and about 78 million people visited them in the summer of 2006.

Water parks boast slides with dozens of loops, incredible speeds and exhilarating drops. The inflatable dry slide on record is the 120-foot (37-meter) "Summit Plummet" in Walt Disney World's Blizzard Beach. If you'd rather ride down on a raft, you can take a plunge on the similarly record-breaking "Insane," an 11-story-tall water slide in Brazil [source: World Waterpark Association]. Whether you're on a mat, a raft or your bare skin, you're at the mercy of gravity as you make your way down -- and sometimes up -- the slippery slope.

A water slide is like a wet roller coaster with no seat and no safety harness, and it uses the same principles a roller coaster does to work. In this article, we'll peek behind the scenes to find out what's involved in operating a water slide, from pumping the water to cleaning it after the ride. We'll also see how the pieces of a wate­r slide fit together and find out what keeps you from flying off into the air as you whip around corners.

At its most b­asic level, a water slide is a relatively tame roller coaster with no track and no car. If you've read , then you know that coaster cars are driven by .

At the beginning of the ride, the coaster car is pulled up the . As the coaster rises higher in the air, its potential energy, or energy of position, increases. Simply put, it has farther to fall. When the coaster is released at the top of the hill, gravity pulls it down the track, converting potential energy to kinetic energy, or energy of motion.

 slides work on exactly the same principle. But instead of a lift hill, you have a stairway. Climbing the stairs builds up a certain amount of potential energy, which turns into kinetic energy as you head down the slide. A taller slide has more potential energy to work with than a shorter slide.

On the inflatable water slide, your body, sometimes combined with a mat or raft, takes the place of the roller-coaster car. Coaster cars have wheels that roll along the track. This reduces the friction between the car and the track, so the car can keep moving. Water slides have a constant stream of water flowing from the top to the bottom. The water lubricates the slide to reduce the friction between the slide and your body.

Apart from total height, the main difference between particular water slides is the way they put the potential energy to work. This is determined by the shape of the slide. We'll look at how a slide's shape affects how fast you fly and how far you move in the next section.

The slide applies a force working against . The balance of these two forces depends on the angle of the slide. When you are sliding along on a nearly level slope, gravity pulls you directly into the slide, and the slide pushes you upward. The upward force of the slide pushes nearly opposite the downward force of gravity, slowing your downward acceleration. When the slope drops sharply, gravity is still pulling you straight down, but the slanted slide is no longer pushing you straight up; it's pushing you at an angle between upward and forward. Since the slide isn't working directly against gravity, you accelerate downward more rapidly.